important.pdf

National Science Olympiad Astronomy C Event 2014

Stellar Evolution and Variable Stars

Chandra X-Ray Public Outreach Office Donna Lee Young, NSO Astronomy Event Supervisor [email protected]

Tad Komacek [email protected]

aavso.org

ASTRONOMY, Division C

DESCRIPTION: Students will demonstrate an understanding of the basic concepts

of mathematics and physics relating to stellar evolution and variable stars.

A TEAM OF UP TO: 2 APPROXIMATE

TIME: 50 minutes

THE COMPETITION: Each team is permitted to bring two laptops, or two 3-ring

binders, or one laptop computer and one 3-ring binder (any size) containing

information in any form from any source. The materials must be 3-hole punched and

inserted into the rings (notebook sleeves are allowable). Each team member is

permitted to bring a programmable calculator. No Internet access is allowed.

Using information which may include Hertzsprung-Russell diagrams, spectra, light curves,

motions, cosmological distance equations and relationships, stellar magnitudes and

classification, multi-wavelength images (X-ray, UV, optical, IR, radio), charts, graphs,

animations and DS9 imaging analysis software, participants will be asked to answer

questions relating to:

a.

The processes and stages of stellar evolution, with an emphasis on the following:

protostars, T Tauri variables, Cepheid variables, semiregular variables, red supergiants,

Mira variables, RR Lyrae variables, neutron stars, magnetars, pulsars, X-ray binaries,

dwarf & recurrent novas, S Doradus variables, Type II & Type Ia supernovas. b.

Use Keplers laws, rotation and circular motion to determine answers relating to the orbital

motions of binary and multiple star systems; use parallax, spectroscopic parallax, and the

distance modulus to calculate distances to Cepheid, RR Lyraes, & Type Ia supernovas.

c.

Students should be knowledgeable about the properties and characteristics of the stages of

stellar evolution listed above, including spectral features and chemical composition,

luminosity, blackbody radiation, color index (B-V), and H-R diagram transitions.

d.

Students will be asked to identify, know the location, be knowledgeable about, and/or

answer questions relating to the three content areas outlined above for the following

Objects: Mira, W49B, Tychos SNR, Vela SNR, G1.9+0.3, Eta Carinae, SS Cygni, T Tauri,

GRS 1915+105, 47 Tucanae, The Trapezium, T Pyxidis, Abell 30, RX J0806.3+1527,

V1647 Ori, V1, NGC 1846, NGC 3132

Eruptive T Tauri

S Doradus

Deep Sky Objects: A. Pulsating Variable Stars

1) Mira Mira variable (Long Period Variable)

2) V1 Cepheid variable

B. Eruptive Variable Stars

1) T Tauri T Tauri variable star

2) V 1647 Ori T Tauri variable star

3) Eta Carinae S Doradus variable star (Luminous Blue Variable)

C. Cataclysmic Variable Stars 1) W49B Type II supernova with black hole

2) Vela Type II supernova with pulsar

3) Tychos SNR Type Ia supernova

4) G1.9+0.3 Type Ia supernova

5) SS Cygni dwarf nova

6) T Pyxidis recurrent nova

D. X-Ray Binaries

1) GRS 1915+105 black hole with companion

Others:

1) J0806.3+1527 two white dwarf binary system

2) Abell 30 & NGC 3132 planetary nebulas

3) 47 Tucanae & NGC 1846 globular clusters

4) The Trapezium stellar nursery

Pulsating Variable Stars: Mira Mira variable

Pulsating Variable Stars: V1 Cepheid

47 Tucanae NGC 1846

Globular Clusters & RR Lyrae Variables

Mira

Instability Strip

Cepheid Instability Strip

RR Lyrae

Instability

Strip

Semiregular Instability Strip

Color Index & Color Magnitude H-R Diagrams

UBV Photometric System

Cosmological Distances

Cepheids

RR Lyrae

Cepheid & RR Lyrae Variable Stars:

Period-Luminosity Relationship and The Distance Modulus

Mv = m - 5log10 (r)

10

Mvsun -Mv* = 2.5 log L*/Lsun

Eruptive Variable Stars: T Tauri T Tauri variable

Eruptive Variable Stars: V 1637 Ori T Tauri

Stellar Nursery The Trapezium

Eruptive Variable Stars: Eta Carinae S Doradus

(Luminous Blue Variable)

Blue Luminous Variables

Eruptive Variables

X

Cataclysmic Variable Stars: W49B Type II Supernova

Cataclysmic Variable Stars: Vela Type II Supernova

Type II Supernova Light Curves

Cataclysmic Variable Stars: Tychos SNR Type Ia Supernova

Cataclysmic Variable Stars: G1.9+0.3 Type Ia Supernova

Cosmological Distances

Cepheids

RR Lyrae

Type Ia Supernovas

The Distance Modulus:

Mv = -19.5 for Type Ia

Type Ia Light Curve with Multiple Filters

Cataclysmic Variable Stars: SS Cygni Dwarf Nova (U Gem)

Cataclysmic Variable Stars: T Pyxidis Recurrent Nova

SS Cygni

T Pyxidis

Light Curves

Cepheid T Tauri

Recurrent Semiregular

Mira

RR Lyrae

Supernova

Dwarf Nova Nova

1) Cepheid light curve

3) Same data plotted twice

2) Superposition of periods

4) Same data starting at maxima

Phase Diagrams

JD today at 1:00 PM 2,456,542.041667

Perfectly Periodic

Correct Epoch

Correct Period

** The slope of each line is the difference between its period and the estimated period.

Perfectly Periodic

Correct Epoch

Wrong Period

**True Period longer

Perfectly Periodic

Change in Period

**True Period Shorter

then Lengthens

Perfectly Periodic

Correct Period

Wrong Epoch

Periodic

Period Unchanged

Epoch has Changed

NOT Perfectly Periodic

Different Period

Each Day

O C Diagrams

Perfectly Periodic

Correct Period Wrong Epoch

MISLEADING H-R Diagrams

X

X

X X

X-Ray Binary: GRS 1915+105

Binary System: J0806.3+1527

Planetary Nebula Abell 30

Planetary Nebula NGC 3132

(Eight-Burst or Southern Ring Nebula)

Planetary Nebula H-R Diagram Tracks

Fusion NOT Burning!!!!

Twinkle twinkle little star, how I wonder

where on the H-R diagram you are.

Blackbody Radiation

Spectra

SS Cygni

Z Cam

Spectra

Sun

Plot

Hydrogen

Balmer Lines

Fraunhofer

He, Ca, H

Lines

Sun

Image

Summary of the Classification of Stars

Spectral

Class

Temperature (oK) Strength of Balmer lines Other lines to look for

O 30,000 - 60,000 weak or not visible Ionized He (4540)

B 10,000 - 30,000 moderate

A 7,500 - 10,000 strong

F 6,000 - 7,500 weak Ionized Ca (3930, 3970) strong compared to neutral H (4340)

G 5,000 - 6,000 weak Ionized Ca (3930, 3970) strong compared to neutral H (4340)

K 3,500 - 5,000 weak or not visible Many lines, neutral Ca 4230

M < 3,500 not visible Many lines

Stellar Radiation Laws:

Plancks Law

Wiens Law

Stefan-Boltzmanns Law

L = 4R2T4

(max = 2.9 x 107 /T)

Basic Equations and Relationships

The Distance Modulus: M = m - 5log10 (r)

10

Keplers 3rd Law: (MA + MB) = a3

p2

v = d ; a = v ; 2 a = vP ; Fc = mac ; ac = v2 = r2

t t r

Small Angle Formula: D = d

206,265

1 pc = 206,265 au = 3.26 ly = 3.08 x 1016m

1 = 60 arcmin = 60 ; 1 = 60 arcsec = 60

Inverse Square Law: L = 1/r2

Circumference, Area, Surface Area, and Volume of a Sphere

chandra.harvard.edu

aavso.org

apod.nasa.gov

http://soinc.org

Variable Star Astronomy

National Astronomy Event Supervisors:

Donna Lee Young [email protected]

Tad Komacek [email protected]

Rules clarifications:

available at www.soinc.org under event information

Event Preparation:

1. Read the Event Description for content and allowable resources.

2. Use the Webinar and PowerPoint for an overview of the content

topics and deep sky objects.

3. Use the Astronomy Coaches Manuel as a guide to collect images

and information for the 2014 competition.

4. Use the APOD, Chandra and AAVSO websites for images and

content.

5. Download the 2013 Astronomy Event from the AAVSO website

to use as a guide for types of questions and for practice.

absolute magnitude

the brightness of an object that would be measured by an observer if the object was

10 parsecs away. It is a measure of the object's luminosity.

absorption line spectrum

dark lines in a continuous spectrum that are produced by cool, thin (low-pressure) gases in

front of a hotter, dense object. Made by electrons jumping up farther from the nucleus of the

atom.

acceleration

a change in motion = (the velocity change)/(time interval of change). It involves a change in

the speed (increase or decrease) OR direction OR both speed and direction.

accretion disk

disk of gas that forms around a massive object as material spirals onto the massive object.

Accretion disks around white dwarfs, neutron stars, and black holes form when material is

drawn off a nearby normal or giant star. Accretion disks around neutron stars and black

holes can be hot enough to radiate X-rays.

active galaxy

luminous galaxy that produces most of its energy from a very compact source at its center. It

has a non-thermal continuous spectrum. The energy is coming from an accretion disk of gas

around a supermassive black hole at the nucleus of the galaxy.

adaptive optics

a technique that compensates for atmospheric turbulence by quickly adjusting the light path

in the optics. This removes seeing effects and enables the telescope to achieve much better

resolution, closer to its theoreticalresolving power.

albedo

the fraction of light reflected from an object. Specified as a decimal fraction from 0 (total

absorption) to 1 (total reflection).

altitude

position on the celestial sphere that is the number of degrees an object is above the nearest

horizon. Varies from 0 at horizon to 90 at zenith. Vertical position of an object.

angular momentum

a measure of the amount of spin or orbital motion an object has. It is proportional to the mass

of the object multiplied by its radius multiplied by its spin or orbital speed.

angular diameter

see angular size.

angular size

the apparent size of an object measured by the angle between two lines of sight along each

side of an object. An object's actual linear diameter can be found from the angular size if the

distance is already known. The linear diameter = (2/360) (its distance angular size in degrees).

annular eclipse

a type of solar eclipse that happens when the Sun and Moon are exactly lined up but the

Moon is too far away from the Earth to totally block the Sun's surface. A ring (annulus) of

sunlight is seen around the dark Moon (contrast with total solar eclipse).

aphelion

point in an object's orbit around the Sun that is furthest from the Sun.

apparent magnitude

the apparent brightness of an object measured by an observer at an arbitrary distance away.

arc minute

a small angle unit = 1/60th of a degree.

arc second

a tiny angle unit = 1/3600th of a degree = 1/60th of an arc minute.

asteroid

boulder to mountain-sized piece of rock remaining from the early solar system. The largest

asteroid is only 1000 kilometers across but most are much smaller.

asteroseismology

study of the internal structure of stars from their pulsations.

astrology

a non-scientific belief system in which the positions of the planets among the stars are

thought to hold the key to understanding what you can expect from life.

astrometric technique (planet detection)

a method of finding exoplanets by looking for a periodic wobbling motion of a star on the

plane of the sky.

astronomical unit

(A.U.): average distance between the Earth and the Sun (149.6 million kilometers). Used for

interplanetary distances.

astronomy

a discipline that uses the scientific method to understand the physical universe (usually

beyond the Earth's atmosphere).

astrophysics

a branch of astronomy that deals with the physical properties and interactions of celestial

bodies---the application of the principles of physics to celestial bodies and phenomena.

aurora australis

aurorae seen in the southern hemisphere.

aurora borealis

aurorae seen in the northern hemisphere.

aurorae

light displays produced by molecules and atoms high up in an atmosphere. The gas particles

are excited by collisions with solar wind particles that were deflected by the planet's

magnetic field toward the magnetic poles of the planet.

autumnal equinox

specific moment in the year (on September 22) when the Sun is directly on the celestial

equator, moving south of the celestial equator.

azimuth

position on the celestial sphere that is the number of degrees along the horizon away from

the exact north point. Exact North = 0, exact East = 90, exact South = 180, exact West =

270, exact North = 360 (or 0). Horizontal position of an object.

Big Bang

a theory of the creation of the universe from an ultra-compact volume with very high

temperatures about 13.7 billion years ago. The ultra-compact volume began expanding and is

responsible for the expanding motion we see today.

bio-marker

spectral signatures of certain compounds in certain proportions that could not be produced

by non-biological processes

black hole

the collapsed core for the most massive stars. Formed from the total collapse of a core

greater than 3 solar masses to an infinitesimal point of infinite density. Gravity in the region

surrounding the collapsed core is so strong that the escape velocity is greater than the speed

of light. Far beyond that region, black holes obey Newton's law of gravity.

blueshift

the shift of spectral lines from an object to shorter wavelengths because the object is

moving toward the observer. The greater the speed of the object, the greater the blueshift

will be.

brown dwarf

object formed from the gravitational collapse of a gas cloud just as a star is but having too

little mass (less than 0.08 solar masses) to undergo nuclear fusion reactions.

carbonaceous meteorite

type of stone meteorite containing silicates, carbon compounds (giving them their dark

color), around 20% water, and sometimes amino acids (the building blocks of proteins used

in biological processes of life).

celestial equator

great circle that is a projection of the Earth's equator onto the sky. Always intercepts horizon

at exact East and exact West point. Its meridian altitude = (90 degrees - observer's latitude).

We see one-half of its circle at a time (12 hours worth).

celestial sphere

imaginary sphere of extremely large size around the Earth on which the stars appear to be

placed.

center of mass

the balance point between two massive objects that is proportionally closer to the more

massive object. It is the point where (mass object 1) (object 1 distance from center of

mass) = (mass object 2) (object 2 distance from center of mass).

centripetal force

a force directed inward.

Cepheid

(variable star): a type of variable star that changes brightness by changing size and

temperature with a period that depends on its average luminosity. More luminous Cepheids

have longer pulsation periods. Cepheids are particularly valuable for determining distances

to the nearby galaxies in which they reside. Distances to Cepheids are derived from

measurements of their pulsation periods and apparent brightnesses and application of

the inverse square law of light brightness.

chondrule

round glassy structure 0.5 to 5 millimeters in diameter embedded in

a primitive stone meteorite. It is a solidified droplet of matter from the early solar nebula and

is the very oldest part of the primitive meteorite.

chromatic aberration

a defect in the images from refractor telescopes that is caused by different colors of light

focussing to different points behind the glass lens. A rainbow of colors is produced around

the image.

chromosphere

the hot, thin layer of the Sun's atmosphere right above its photosphere.

circumpolar

when an object is close enough to either the north celestial pole or south celestial

pole (within an angular distance = observer's latitude) such that the object never moves

below an observer's horizon or never rises above the horizon as the Earth rotates.

climate

long-term average of weather (usually 30 years or longer for Earth climate). Can change

only on long time scales of decades or more.

closed universe

a universe with enough matter (gravity) to eventually stop the expansion and recollapse (it

has a "closed future").

color-magnitude diagram

a plot of the colors (temperatures) and magnitudes of stars. Another name for

the Hertzsprung-Russell diagram.

coma

(comet): large atmosphere around a comet's nucleus that forms when the nucleus nears the

Sun and warms up (usually at around Saturn's or Uranus' distance from the Sun).

conservation of angular momentum

when an object or system of objects has no net outside forces acting on it, the total amount of

its angular momentum does not change.

continuous spectrum

a spectrum that has energy at all wavelengths (a full rainbow). See also thermal spectrum.

convection

means of energy transport through the bulk motion of a fluid. Warmer fluid is less dense and

rises upward releasing its excess energy to the cooler environment and cool, higher density

fluid sinks.

convection zone

the region of a star's interior where energy is transported outward using bulk motions of

rising hot gas and sinking cool gas. For the Sun, it is the region above the radiative zone.

core

(stellar): the center of a star where the density and temperature are high enough for nuclear

fusion to occur.

coriolis effect

the deflection sideways of an object moving across the surface of a rotating body caused by

the rotation of the body. The coriolis effect makes storms spiral on the Earth and produces

the banded cloud layers on the gas giant planets.

correlation

a mutual relationship between two properties (usually such that an increase in one property is

seen when another property increases).

corona

the top layer of the Sun's atmosphere. It is up to a few million degrees in temperature, but

has very low density so the amount of heat is small. It is the pearly-white "crown" or glow

seen around the dark Moon during a total solar eclipse.

cosmic microwave background radiation

radio (microwave) energy that is nearly uniform in all directions and has a nearly perfect

thermal spectrum. It is the greatly redshifted remnant of the early hot universe produced

about 380,000 years after the birth of the universe.

cosmic rays

extremely high-energy (very fast-moving) sub-atomic particles, mostly protons, in space.

Some produced by the Sun. Others produced in star deaths such as supernovae. Highest

energy cosmic rays are of unknown origin.

cosmological constant

an extra term Albert Einstein put in his equations of General Relativity that would act as a

repulsive form of gravity to balance the attractive nature of gravity and keep the universe

static.

cosmological principle

an assumption that the universe is everywhere uniform and looks the same in any direction---

it is homogeneous and isotropic.

cosmology

the study of the nature and origin of the universe and how it changes over time.

critical density

boundary density between enough mass/volume to eventually stop the expansion of the

universe and too little mass/volume to eventually stop the expansion.

dark energy

an additional energy needed to make the universe's overall curvature flat. It may be

the cosmological constant.

dark matter

material that does not emit any light (or not detected yet), but has a significant gravitational

effect.

declination

(dec): position on the celestial sphere that is the number of degrees an object is north or

south of the celestial equator. It is a projection of latitude lines onto the sky. An object's

declination is fixed with respect to the stars. Varies from --90 at the SCP to 0 at the

celestial equator to +90 at the NCP. Vertical position of an object.

degenerate gas

super-compressed gas that behaves more like a solid and whose properties must be described

by quantum mechanics. The pressure of degenerate gas does not depend on the temperature.

density

how much material an object has in the space it occupies: density = mass/volume.

deuterium

an isotope of hydrogen with one proton and one neutron in the nucleus.

differentiated

when the interior of a large object has undergone differentiation so that denser material lies

closer to the object's core.

differential rotation

(galaxy): stars closer to a disk galaxy's center complete a greater fraction of their orbit in a

given time than stars farther out from the center, so that adjacent parts of the galactic disk do

not always stay close to each other.

differentiation

the separation of materials in a fluid under the influence of gravity such that the denser

material collects at the core while the less dense material rises to the surface.

direct image technique

(planet detection) method of finding exoplanets by taking a picture of them.

discrete spectrum

a spectrum that is not continuous---an emission line spectrum or an absorption line spectrum.

dissociation

the splitting apart of a molecule into its constituent atoms, e.g., the splitting of water

molecules into hydrogen and oxygen when water vapor is struck by ultraviolet light.

doppler effect

an apparent change in the wavelength of energy produced by an object that is caused by the

object's motion towards or away from the observer (along the line of sight). In astronomical

spectra, the doppler effect is seen in the shifting of spectral lines.

doppler shift technique

(planet detection) method of finding exoplanets by looking for a periodic

alternating redshift and blueshift of a star.

Drake Equation

an equation that estimates the number of communicating advanced civilizations inhabiting

the Galaxy.

dust

one component of the interstellar medium that is made of thin, highly flattened flakes or

needles of graphite and silicates coated with water ice and other frozen gases. It is

responsible for the reddening and extinction of starlight.

dust tail

(comet): one of the two tails of a comet made of dust grains that curves away from the Sun

from the action of the photons in the sunlight pushing the dust grains away from Sun. It has a

yellow-white color from reflected sunlight.

eccentricity

measures how far from a circular shape an ellipse is. Numerically, the eccentricity e = 1 --

(perihelion / semi-major axis). The eccentricity e = 0 for a circle and e = nearly one (1) for

very long, skinny ellipses.

eclipsing binary

two stars orbiting each other in a plane that is along your line of sight so you see one star

periodically pass in front of the other star. They are especially useful for determining the

diameters and masses of stars.

ecliptic

great circle that is a projection of the Earth's orbit onto the sky, or the path the Sun takes

through the stars in its annual motion. It is tilted by 23.5 with respect to the celestial

equator.

electromagnetic radiation

a form of energy made of oscillating electric and magnetic fields. It is a fancy word for

``light'' and it includes (in order of increasing energy) radio, infrared, visible light (optical),

ultraviolet, X-rays, and gamma rays.

electron

negatively-charged subatomic particle that moves around the atomic nucleus in specific

energy levels. It has about 1800 times less mass than the proton and neutron.

electron degeneracy pressure

pressure exerted by a degenerate gas made of electrons. It is what prevents further collapse

of a white dwarf.

element

a substance that cannot be decomposed by chemical means into simpler substances. All

atoms of an element have the same number of protons in the nucleus.

ellipse

squashed circle that tapers at both ends. The total of the distance between any point on the

ellipse and one focus + the distance from the point to the other focus = a constant. It is the

shape of bound orbits.

elliptical galaxy

a galaxy with a smooth, rounded appearance. Early large burst of star formation long ago

used up all of their original gas and dust. Star orbits are aligned in more random directions

and have greater eccentricities than star orbits in spiral galaxies.

emission line spectrum

bright lines in a spectrum that are produced by hot, thin (low-pressure) gases. Made

by electrons jumping down closer to the nucleus of the atom.

epicycle

a device in Ptolemy's Earth-centered model that makes a planet execute a small circular

motion around a point that is itself in a circular orbit around the Earth. It was used to

explain retrograde motion.

equation of state

the relation that describes the state or condition of a material as determined by how the

temperature, density, and pressure depend on each other in the material.

Equation of Time

a relation that describes the difference in time between the meridian crossings of the mean

Sun and the actual Sun.

equinox

point on the sky where the ecliptic and the celestial equator intercept. When the Sun is at the

equinox point, it is on the celestial equator and we have 12 hours of daylight. Vernal (spring)

equinox: March 21; autumnal equinox: September 22.

equivalence principle

states that there is no experiment a person could conduct in a small volme of space that

would distinghish between a gravitational field and an equivalent uniform acceleration. This

principle is the foundation of General Relavity.

erosion

the breaking down or building up of geological structures and transporting of material by ice,

liquid, or wind.

escape velocity

the initial speed an object needs to escape a massive body's gravitational influence and never

return.

event horizon

the distance from a black hole's center at which the escape velocity equals the speed of light.

No information of events occurring inside the event horizon can get to the outside.

exoplanet

a planet orbiting another star (other than our Sun) beyond our solar system.

exosphere

uppermost layer a planet's atmosphere where the gases escape to space. Very low density

gases heated by X-rays and ultraviolet light.

extinction

reduction in the intensity of the light (the number of photons) from a celestial body as the

light passes through a dust cloud. Dust clouds in space make stars behind the dust clouds

appear dimmer than they would be if the dust was not there.

extremophile

living organism that survives (even thrives) in extreme environments such as very hot or

very cold temperatures, very acidic or very basic conditions, or very high pressures.

filter

thin material that is transparent to only a narrow range of wavelengths of light.

flat universe

a universe that stop expanding only after an infinite amount of time (a special case of an

open universe).

flux

the amount of energy passing through a given area (e.g., one square centimeter) in a second.

It is the apparent brightness of an object.

focus

one of two special points along the long axis of an ellipse such that the addition of the

distances (satellite to focus#1) plus (satellite to focus#2) always equals the same numerical

value. It is not at the center of the elliptical orbit unless the orbit is perfectly circular.

force

any action or influence that causes an acceleration.

frequency

the number of wave crests that pass a point every second. Measured in hertz (Hz). For

electromagnetic radiation, the frequency is inversely proportional to the wavelength.

galactic cannibalism

the swallowing up whole of a small galaxy by a large galaxy (usually a large elliptical galaxy

at the center of a galaxy cluster).

galaxy

a very large cluster of stars (tens of millions to trillions of stars) gravitationally bound

together.

General Relativity

a theory invented by Albert Einstein to describe gravity. It says that gravity is a warping or

distortion of spacetime around a massive object. Although it applies everywhere in the

universe, General Relativity must be used instead of Newton's law of gravity in regions of

strong gravity.

geocentric

(universe): model of the universe with the Earth at the center and all other objects moving

around it.

giant impact theory

explanation about how the Moon was formed from mantle material blown out by the impact

of a Mars-sized (or larger) planet with the Earth several billion years ago. The ejected

material condensed to form the Moon.

giant molecular cloud

large, dense gas cloud (with some dust) that is cold enough for molecules to form. A typical

giant molecular cloud has a few hundred thousand to a few million solar masses of material.

Stars form in them.

globular cluster

spherical cluster of hundreds of thousands to millions of very old stars. The orbits of most

globular clusters are very elliptical and oriented in random directions.

granulation

bright spots of convection on the Sun's surface 700 to 1000 kilometers across forming a

honeycomb pattern. Formed from hot, bright gas rising from below in the center of a granule

and cooler, dimmer gas falling back down at the edge of a granule.

gravitational lens

the focussing of light from a distant object by the warped space-time around a massive body

(such as a galaxy) between you and the distant object as predicted by General Relativity.

gravitational redshift

the lengthening of the wavelength of electromagnetic radiation as it moves away from a

region of intense gravity.

gravity

a fundamental force of nature between two objects that is proportional to the product of their

masses and inversely proportional to the square of the distance between their respective

centers. It depends on nothing else.

greenhouse effect

the trapping of heat energy close to a planet's surface by certain types of gases in the

atmosphere (e.g., water, methane, and carbon dioxide). These gases allow visible light from

the Sun to reach the surface but prevent the infrared light from the heated surface to radiate

back to space.

ground state

the lowest energy state of an atom---all of the electrons are as close to the nucleus as

possible.

H II region

cloud of ionized hydrogen around a hot, luminous star (usually O or B-type). Produced by

the copious ultraviolet light from the hot star(s) causing the hydrogen to fluoresce (atoms are

ionized and then when the electron recombine, they produce energy in the visible band).

habitable zone

the region around a star where the temperature on a planet's surface is between the freezing

point (0 C) and boiling point (100 C) of water.

half-life

the time required for one-half of a radioactive material to decay to a more stable material (it

is NOT one-half the age of the rock!).

heliocentric

(universe): model of the universe with the Sun at the center and all other objects moving

around it.

helioseismology

the study of the Sun's interior from observations of the Sun's pulsations on its surface.

helium flash

in low-mass red giant stars, the onset of the fusing of helium in the core can be very rapid,

almost explosive.

hertz

(Hz): unit of frequency. One hertz = 1 wave peak/second.

Hertzsprung-Russell diagram (H-R diagram)

a plot of stellar luminosity vs. temperature invented by two astronomers, Hertzsprung and

Russell. High temperatures are on the left side and decrease to the right. Low luminosities

are on the bottom and increase vertically.

homogeneous

everywhere uniform in appearance so that there is no preferred observing position.

Hubble constant

slope of the line relating the speed of the galaxies away from each other and their distance

apart from each other.

Hubble Law

the relationship between a galaxy's recession speed from other galaxies and the distance

between them: the recession speed = H distance, where H is the Hubble constant. The

recession speed is derived from theredshift of the galaxy spectra and with the Hubble Law, it

can be used to find the distance to the farthest galaxies.

hydrostatic equilibrium

a balance between the compression from the weight of material above a layer and the

expansion of an outward-directed pressure below the layer. In normal stars and planet

atmospheres, the outward-directed pressure is supplied by the thermal pressure of warm or

hot gases.

hypothesis

an unproven or unverified idea or model.

ideal gas law

the equation of state for simple gases: pressure = (k density temperature)/(molecular

weight of the gas), where density is the mass density. If use number density (#

particles/volume), pressure = (k number density temperature), where k is the Boltzmann

constant.

impact cratering

the process of creating round, bowl-shaped depressions on a surface by the explosion of a

large body striking the surface.

inertia

the property of an object describing its tendency to stay at the same velocity (or at rest)

unless a force acts on it.

inflation

a brief period of ultra-rapid expansion in the very early universe about 10-38 to 10-36 seconds

after the Big Bang.

instrumentalism

a way of viewing scientific theories and models that says they are merely tools or calculation

devices and are not to be interpreted as reality.

intensity

the number of waves or photons reaching your detector every second.

interferometer

an array of telescopes connected electronically to act as one large telescope with much

improved resolution. The resolution of the interferometer is equal to a single telescope

having a diameter equal to the length of the interferometer.

interstellar medium

the gas and dust between the stars.

inverse square law of light brightness

an object's apparent brightness decreases with the square of the distance. The apparent

brightness is the amount of energy flowing through a given area in a given amount of time.

ion

a particle with an electrical charge (the number of electrons is different than the number

of protons).

ion tail

(comet): one of the two tails of a comet made of ionized particles that points directly away

from the Sun from the action of the solar wind. It has a bluish color from the emission lines

mostly of ionized carbon monoxide.

irregular galaxy

a galaxy with no definite structure. Stars are distributed in bunches placed randomly

throughout the galaxy. Many irregular galaxies have a lot of gas and dust still left in them

from which stars are now forming.

isotope

a sub-group of an element in which the atomic nucleus has the same number of neutrons, as

well as, the same number of protons. All of the atoms of an element will have very nearly the

same chemical properties, but the isotopes can have very different nuclear properties.

isotropic

exhibiting the same property when looking in any given direction.

Kelvin scale

a temperature scale that directly scales with the random motion energy of a substance, such

that 0 Kelvin is at absolute zero (state where all random motion ceases) and higher

temperatures have non-zero Kelvin values. It scales like the metric system's Celsius scale for

increasing temperatures---every degree interval of the Kelvin scale corresponds to the same

change in the random motion energy as a degree interval of the Celsius scale: # Kelvin = #

Celsius - 273.

Kepler's 1st law

orbits are ellipses with the central object at one focus (not the center!). There is nothing at

the other focus.

Kepler's 2nd law

a line between the satellite and the central object sweeps out equal areas in equal intervals of

time. A satellite moves faster when it is closer to the massive body it orbits and moves

slower when farther from the massive object.

Kepler's 3rd law

for an object in an elliptical orbit around a massive body, the square of the orbital period is

proportional to the cube of the average distance of the orbiting object from the massive body.

The massive body's mass is proportional to the (average distance)3/(orbital period)2. In

general, for two objects orbiting a common point between them, their combined mass is

proportional to: (average distance between them)3/(their orbital period)2.

kilogram

unit of mass in the metric system.

kinetic energy

the energy something has because of its motion = 1/2massvelocity2.

Kuiper Belt

a disk of comets beyond Neptune's orbit (or 30 to 100+ A.U.) that orbit roughly in the same

plane as the planets. Many of the short period comets come from the Kuiper Belt.

latitude

used to specify position on the Earth, it is the number of degrees north or south of the Earth's

equator.

law of gravity

(Newton's): the force of mutual attraction between two objects = G(mass #1) (mass #2) /

(distance between the objects)2. The term G is a universal constant of nature that always =

6.672 10-11meter3/(kilogram second2).

life zone

the region around a star where the temperature on a planet's surface is between the freezing

point (0 C) and boiling point (100 C) of water.

light curve

a plot of how an object's brightness changes over time.

light-gathering power

the ability of a telescope to collect more light than the human eye in a given amount of time.

It depends on the area of the telescope's objective, such that the larger the collecting area of

the objective, the brighter the image will be.

lighthouse model

a model describing how pulsars pulsate: the rapidly rotating neutron star produces a narrow

beam of light from its magnetic field and if the magnetic pole is aligned with the Earth, the

narrow beam of light sweeps over us periodically like the beam of a lighthouse does for

ships at sea.

light year

distance light travels in one year (9.461 trillion kilometers, over 63,000 A.U.!). Used for

interstellar distances.

line of nodes

the intersection of a planet's or the Moon's orbit with the Earth's orbit.

lithosphere

the layer of hard rock that includes the crust and the outermost part of the mantle in a

terrestrial planet.

local noon

when the Sun is on an observer's meridian.

long period comet

a comet with an orbit period of thousands to millions of years long that comes from the Oort

cloud.

longitude

used to specify position on the Earth, it is the number of degrees east or west of the 0 line

going through Greenwich, England.

luminosity

the total amount of energy radiated by an object every second.

lunar eclipse

when the shadow of the Earth hits the Moon at exactly full phase.

magnetic dynamo

a mechanism thought to produce magnetic fields in a planet by the swirling, or circulation, of

liquid conducting material in or near the planet's core.

magnifying power

the ability of telescope to enlarge images. Can be increased by using an eyepiece with a

shorter focal length.

magnitude

used to quantify brightness. Based on the ancient system of Hipparchus but refined and

quantified for measurements today such that a ratio of 100 in brightness corresponds to a

magnitude difference of 5. Fainter objects have larger, positive magnitudes (closer to

positive infinity), while brighter objects have lower magnitudes (closer to negative infinity).

main sequence

the narrow diagonal band in the Hertzsprung-Russell diagram going from upper left to lower

right describing the characteristics of 90% of the stars. Stars spend about 90% of their lives

in this stage and are fusing hydrogen to create helium.

main sequence turnoff

the mass of the most massive main sequence star remaining in a star cluster. Stars more

massive than the turnoff have already evolved beyond the main sequence stage. The turnoff

mass can be used to determine the age of the star cluster (it equals the lifetime of the most

massive star still in the main sequence stage).

mass

an intrinsic property of an object that measures its resistance to an acceleration. Mass is

measured in units of kilograms.

mathematical models

a set of equations describing the structure and interaction of material in an object or group of

objects.

mean Sun

imaginary object that moves uniformily eastward along the celestial equator such that it

completes one 360 circuit of the sky in one year. The average solar day is the time between

successive meridian crossings of the mean Sun.

meridian

great circle on the sky that goes through the celestial poles and the zenith point. It separates

the daytime motions of the Sun into ``a.m.'' and ``p.m.''. The azimuth of an object on the

meridian in the northern sky = 0 and the azimuth of an object on the meridian in the

southern sky = 180.

mesophere

layer of a planet's atmosphere above a stratosphere where the temperature decreases with

increasing altitude.

metals

what astronomers call all of the elements heavier than helium (like carbon, nitrogen, oxygen,

sodium, aluminum, chlorine, calcium, iron, etc.).

meteor shower

what happens when the Earth passes through the dust trail left by a comet in its orbit. The

dust grains are the size of a grain of sand or smaller and produce a large number of meteors

in a short time that appear to come from a particular point in the sky.

meteorite

a small rock from space that makes it to the surface of a planet without burning up in the

planet's atmosphere. This distinguishes it from when it is passing through the atmosphere,

glowing hot from the friction with the atmosphere and is called a meteor.

microlens technique (planet detection)

a method of finding exoplanets by looking for the gravitational lensing effect from a planet

orbiting a foreground star added to the gravitational lensing effect of the foreground star on

the light from a more distant star.

Milky Way Galaxy

the large spiral galaxy in which our Sun and planets reside. Our Sun is one star of several

hundred billion in the Milky Way.

model

an abstract construct or idea that is a simplified view of reality. It must enable you to make

testable predictions of what will happen under new circumstances.

nanometer

a very tiny distance equal to one-billionth of a meter (0.000000001 meter).

natural selection

the primary mechanism of evolution by which, over time, heritable traits that enhance

survival and successful reproduction will become progressively more common in succeeding

generations in any local environment. It is a NON-random process that produces adaptations.

neap tide

tide that has a small change between low and high tide. It occurs at first and third quarter

phase, when the Moon's tidal effect is perpendicular with the Sun's tidal effect.

neutrino

a sub-atomic particle with very small mass that is produced in nuclear fusion reactions and

rarely interacts with ordinary matter. Neutrinos travel at the nearly the speed of light and

provide current information about the number of nuclear fusion reactions occurring in a star's

core (in the case of the Sun, the information is only about 8.3 minutes old).

neutron

subatomic particle with zero charge (neutral charge) that is found in the nucleus of an atom.

It is slightly more massive than the positively-charged proton.

neutron degeneracy pressure

pressure exerted by a degenerate gas made of neutrons. It is what prevents further collapse of

a neutron star.

neutron star

the collapsed core for an intermediate to high-mass star. The core is more than 1.4 solar

masses but less than 3 solar masses and is about the diameter of a city. The pressure

from degenerate neutrons prevents further collapse.

newton

unit of force in the metric system. It is used to specify the amount of weight.

Newton's 1st law

(of motion): a body at rest remains at rest, and one moving in a straight line maintains a

constant speed and same direction unless it is deflected by a force.

Newton's 2nd law

(of motion): the amount of force needed to cause an acceleration depends on an object's

mass, such that the force applied = the mass of an object its acceleration.

Newton's 3rd law

(of motion): for every action force ON an object, there is an equal but opposite force BY the

object.

north celestial pole

(NCP): projection of the Earth's north pole onto the sky. The NCP altitude = the observer's

northern latitude.

nova

an object that greatly increases in brightness rapidly, so it appears as a ``new star''. It is

caused by the buildup on a white dwarf's surface of hydrogen gas from a companion star to

the point where the hydrogen fuses explosively into helium. The super-rapid fusion does not

blow up the white dwarf, so the process can repeat itself (contrast with a Type I supernova).

nuclear fusion

the process used by stars to generate energy: less-massive nuclei are fused together under

extremely high temperatures and densities to form more-massive nuclei plus some energy.

The energy comes from the transformation of some of the mass into energy.

nucleus

(comet): the ``dirty iceberg'' about the size of a city from which all of the stuff in a comet

comes from. Irregularly-shaped it is made of dust and frozen gases.

Occam's Razor

a way of approaching the development of a scientific model based on the belief that ``the

best model is the simplest one---the one requiring the fewest assumptions and modifications

in order to fit the observations'' (i.e., nature prefers the simplest most elegant solution).

objective

the primary optical element of a telescope, it gathers the electromagnetic radiation and does

the initial focussing.

Olbers' Paradox

the problem that if the universe is infinite in size and age, then the night sky should

everywhere be as bright as the Sun because no matter which direction you look, your line of

sight will see a star or galaxy.

Oort Cloud

a large spherical cloud of billions to trillions of comets surrounding the Sun at distances

between roughly 50,000 to 100,000 A.U. from the Sun. It has not been directly observed; its

presence is inferred from the behavior and orbits of the long period comets.

opacity

a measure of a material's ability to absorb or block photons. A material with high opacity

prevents most of the photons from passing through (the material is opaque).

open universe

a universe with too little matter (gravity) to stop the expansion (it has an ``open future'').

ozone

a type of oxygen molecule made of three oxygen atoms bound together (O3). This molecule

absorbs ultraviolet light.

paradigm

a general agreement of belief of how the world works; what could be called ``common

sense''.

parallax

an apparent shifting of an object's position resulting from observing the object from two

different vantage points. Stellar parallaxes are seen when we view nearby stars from opposite

sides of the Earth's orbit.

parsec

(pc): distance at which an object would have a parallax of one arc second. Equals

approximately 3.26 light years or about 206,265 astronomical units.

penumbra

region of partial shadow that is outside the umbra; the light source is partially blocked.

perfect cosmological principle

an assumption that the universe is everywhere uniform and looks the same in any direction

in all space and time---it is the same everywhere and does not change throughout time.

perihelion

point in an object's orbit around the Sun that is closest to the Sun.

period-luminosity relation

how the average luminosity of Cepheid variable stars depends on their period of pulsation.

photon

a distinct ``chunk'' or particle of electromagnetic radiation.

photosphere

the thin layer of the Sun where the gas just becomes thin enough for the photons from the

interior can escape to space. It is the ``surface'' of the Sun.

photosynthesis

a process used by plants to convert water, carbon dioxide, and sunlight into carbohydrates

and oxygen. The oxygen in the Earth's atmosphere is produced by this process.

planetary nebula

final mass-loss stage for a dying low-mass star in which the outer layers are ejected during

the core's collapse to form a white dwarf.

plate tectonics

the scientific theory that describes the process of the movement of pieces of the

Earth's lithosphere (called "plates") and how it explains the Earth's surface geology.

poor cluster

galaxy cluster with only a few tens of galaxies.

Population I

(stars): younger stars including the hot blue stars that have slightly elliptical orbits closely

aligned with the disk plane of the Milky Way Galaxy. The youngest stars are found in the

spiral arms of the galactic disk.

Population II

(stars): older, redder stars that have very elliptical orbits randomly oriented and are found in

the stellar halo and bulge of the Milky Way Galaxy.

precession

slow wobble of an object's rotation axis or an object's orbit. The precession of the Earth's

rotation axis is caused by the gravitational pulls of the Sun and the Moon on the Earth's

equatorial bulge.

pressure

amount of force per unit area: pressure = force/area.

primitive

in studies of the solar system, an object or rock that has remained chemically unchanged

since it formed (solidified) about 4.6 billion years ago. The object holds a record of the very

early conditions from which the rest of the solar system (Sun, planets, moons) formed.

proper motion

angular distance an object moves across the sky (perpendicular to your line of sight) in a

given amount of time.

proton

positively-charged subatomic particle that is found in the nucleus of an atom. It has about

1800 times more mass than its negatively-charged electron counterpart.

proton-proton chain

a nuclear fusion chain reaction used by most stars to generate energy. In a chain process

involving three or more reactions, the net result is four hydrogen nuclei are fused together to

form a helium nucleus plus energy.

protostar

collapsing clump of dust and gas that will later become a star. The protostar is warm enough

to produce a lot of infrared and some microwave radiation. Microwave energy is produced

by the surrounding cocoon cloud.

pulsar

young neutron star with a strong magnetic field and rapid rotation that produces beams of

radiation out of its magnetic poles. If the beams cross our line of sight, we see the star

``pulsate'' (flash on and off).

Pythagorean paradigm

``common sense'' belief articulated by Pythagoras about the universe that says all objects

move in perfectly circular orbits at perfectly uniform speeds and the Earth is at the center of

the motions of celestial bodies.

quasar

short for ``quasi-stellar radio source''. Quasars are the most luminous of active galaxies---

they are the extremely active nuclei of otherwise normal galaxies. Quasars generate a huge

amount of energy within very tiny volumes. Because they are most luminous things known,

quasars can be seen at very large distances. Looking like blue stars, they can be

distinguished from stars by the presence of broad emission lines instead of the

narrow absorption lines of normal stars, their large redshifts because of their very large

distances (see the Hubble Law), and many quasars are strong radio sources, unlike stars

which have weak radio emission.

radial velocity

the velocity along the line of sight.

radial velocity curve

a plot of how an object's velocity along the line of sight changes over time.

radiative zone

the region of a star's interior where energy is transported outward with photons. For the Sun,

it is the region above the core.

radio galaxy

usually an elliptical galaxy emitting very large amounts of radio energy from the core (up to

millions of times a typical galaxy's radio emission) and having strong radio emission from

regions extending out several million light years from the galaxy nucleus.

radioactive dating

a technique that gives absolute ages of a material (rather than merely relative ages) from the

number of radioactive active atoms remaining in the material.

realism

a way of viewing scientific theories and models that says they truly characterize the way the

universe operates; they represent reality (contrast with instrumentalism).

recombination

process of electrons becoming bound to protons to make neutral atoms.

reddening

the preferential scattering of the shorter wavelengths of light as it passes through a dust

cloud, so that a large fraction of the bluer wavelengths of light are scattered away from your

line of sight while a large fraction of the redder wavelengths of light make it through the dust

cloud unaffected. Dust clouds in space make stars behind the dust clouds appear redder than

they would be if the dust was not there.

red giant

a dying star that has become large in diameter and cool on the surface while the core has

shrunk and increased in temperature. Nuclear fusion takes place in a shell around the

compressing core. They are more luminous than when the star was in the main

sequence stage, even though their surface is cool, because they have a HUGE surface area.

Therefore, they are plotted in the upper right part of the Hertzsprung-Russell diagram.

redshift

the shift of spectral lines from an object to longer wavelengths because the object is

moving away from the observer. The greater the speed of the object, the greater the redshift

will be.

reflector telescope

telescope that uses a large mirror at the back of the telescope to gather and focus the light. It

has no size limit and is the type preferred for large research telescopes.

refraction

the bending of waves when they pass from one transparent medium (or vacuum) to another

(e.g., sunlight bending as it passes through the Earth's atmosphere).

refractor telescope

telescope that uses a large glass lens at the front end of the telescope to gather and focus the

light. The glass lens has a maximum size limit and suffers to some degree from chromatic

aberration.

representative sample

a collection of objects that includes all parts of the population of the objects in their proper

proportions; an unbiased sample that gives accurate results.

resolving power

the ability of a telescope to detect very small details and produce sharp images. It depends on

the diameter of the telescope's objective or the interferometer AND the wavelength of light

used to observe, such that the more wavelengths that can be fit across the objective or

interferometer, the sharper the image will be.

retrograde motion

when a solar system object (e.g., a planet) moves ``backward'' (westward) with respect to its

normal eastward drift against the stars. It happens when the Earth is closest to the object.

rich cluster

a cluster of hundreds to thousands of galaxies.

right ascension

(RA): position on the celestial sphere measured with respect to the vernal equinox position

on the celestial equator. It is a projection of longitude lines onto the sky and converted to

time units. An object's right ascension is fixed with respect to the stars. Varies from 0h at

the vernal equinox point to 24h in a full circle.

rotation curve

how the orbital velocities of objects in the disk of a spiral galaxy vary with increasing

distance from the center of the galaxy. The rotation curve is used to study the distribution of

mass in a galaxy.

RR Lyrae

(variable star): a type of low-mass variable stars that all have the same average luminosity.

RR Lyrae are valuable for determining distances to star clusters.

runaway greenhouse

a process in which the heating of a planet increases the greenhouse effect in a feedback loop

resulting in a dramatic change in the atmospheric composition and dramatic rise in the

surface temperature. Venus' atmosphere is an example of this process.

runaway refrigerator

a process in which the cooling of a planet's surface decreases the greenhouse effect in a

feedback loop resulting in a dramatic change in the atmospheric composition and dramatic

cooling in the surface temperature. Mars' atmosphere is an example of this process.

Schwarzschild radius

the distance from a black hole's center at which the escape velocity equals the speed of light

(same as the event horizon).

season

approximately three-month period bounded by an equinox and a solstice.

seeing

a measure of the amount of turbulence of the air. When the seeing is ``good'', the amount of

turbulence is small and the images are steady (little twinkling). ``Poor'' seeing occurs when

the atmosphere is turbulent so the images shimmer and dance around (more twinkling).

seismology

the study of a planet's interior from observations of how seismic waves (``earthquake

waves'') travel through the interior.

semi-major axis

the distance between the center of an elliptical orbit and one end of the orbit along the long

dimension of the elliptical orbit. It equals the average distance between two orbiting objects.

Seyfert galaxy

a spiral galaxy with a compact, very bright nucleus that produces a non-thermal continuous

spectrum with broad (fat) emission lines on top.

shell burning

nuclear fusion that is occurring in a layer outside a star's core instead of inside the core as the

core compresses. The fusion rate is faster than before and the outer layers are pushed

outward to form a red giant.

short period comet

a comet with an orbit period less than about 200 years long that comes from the Kuiper Belt.

sidereal day

time between successive meridian crossings of a star. It is the true rotation period of a planet

(on Earth, one sidereal day = 23 hours 56 minutes 4.09 seconds). Rotation rate of the Earth =

1 every 4 minutes (actually 3.989 minutes). The Earth's sidereal day is four minutes shorter

than the solar day our clocks are based on so a star crosses the meridian 4

minutes earlier than it did the previous night.

sidereal period

the period of revolution of one object around another measured with respect to the stars (e.g.,

for the Moon, it is 27.3 days).

sidereal year

the time required for the Earth to complete an exactly 360 orbit around the Sun as measured

with respect to the stars = 365.2564 mean solar days (contrast with tropical year).

solar day

time between successive meridian crossings of the Sun. Our clocks are based on this interval

of time (on Earth, one solar day = 24 hours on average).

solar eclipse

when the shadow of the Moon hits the Earth at exactly new phase. The Moon covers up part

or all of the Sun.

solar luminosity

unit of power relative to the Sun. One solar luminosity is about 4 x 1026 watts.

solar mass

unit of mass relative to the Sun. One solar mass is about 2 x 1030 kilograms

solar neutrino problem

the number of neutrinos observed to be coming from the Sun's core is significantly less than

what was predicted by the original solar interior models. Discovery of the oscillation of

neutrino types solved the problem.

solar wind

fast-moving, charged particles (mostly protons, electrons, and helium nuclei) flowing

outward from the Sun's upper atmosphere, the corona.

solstice

point on the sky where the ecliptic is furthest from the celestial equator by 23.5. When the

Sun is at the solstice point we have either the longest amount of daylight (summer: June 21

for northern hemisphere) or the shortest amount of daylight (winter: December 21 for

northern hemisphere).

south celestial pole

(SCP): projection of the Earth's south pole onto the sky. The SCP altitude = the observer's

southern latitude.

spacetime

the four-dimensional combination of space (three dimensions) and time (the fourth

dimension). As a consequence of Special Relativity, time and space are not independent of

each other and are relative to the motion of an observer.

Special Relativity

a theory invented by Albert Einstein to describe measurements of length and time for objects

moving at constant velocity. Although it applies to all motion at constant velocity, it must be

used instead of Newton's laws of motion at speeds of greater than about ten percent the

speed of light.

speckle interferometry

method that compensates for atmospheric turbulence by taking many fast exposures of an

object to freeze the effect of seeing. Computer processing of the multiple exposures removes

atmospheric and instrument distortions to produce high-resolution images at the telescope's

theoretical resolving power.

spectral type

(also spectral class) the classification of a star according to its temperature as measured from

the strengths of its spectral lines. In order of temperatures from hottest to coolest the spectral

types are O B A F G K M. This is also the order of luminosity and mass (most luminous and

most massive to dimmest and least massive).

spectroscopic binary

two stars orbiting a common point at too great a distance away from us to resolve the two

stars individually, but whose binary nature is indicated in the periodic shift of their spectral

lines as they orbit around each other.

spectroscopic parallax

a method of determining distances to stars from knowledge of the luminosity of their spectral

types and measurement of their apparent brightness. The distances are derived from

the inverse square law of light brightness.

spectroscopy

the analysis of an object from its spectrum.

spectrum

display of the intensity of light at different wavelengths or frequencies.

spherical aberration

a defect seen in images that is caused by the objective not being exactly shaped (e.g., an

objective mirror not being exactly parabolic) so that not all of the light is focussed to the

same point.

spiral galaxy

a highly flattened galaxy with a disk and a central bulge. The disk has a spiral pattern with

slightly more stars and gas than in the rest of the disk. A slow, steady star formation rate

means that they still have gas and dust left in them from which stars are still forming. The

star orbits are constrained to stay within a small distance from the mid-plane of the disk and

have small eccentricities.

spring tide

tide that has a large change between low and high tide. It occurs at new and full phase, when

the Moon's tidal effect is aligned with the Sun's tidal effect.

standard candle

luminous objects of a known luminosity used to measure large distances via the inverse

square law of light brightness.

starburst galaxy

a galaxy undergoing a large burst of star formation usually as a result of a collision or

merger of two galaxies. It can produce as much light as several hundred ``normal''

undisturbed galaxies.

Stefan-Boltzmann law

relation between the amount of energy emitted by a unit area on an object producing

a thermal spectrum and its temperature: energy in Joules emitted by one square meter =

5.67 10-8 temperature4. The temperature is in Kelvin.

stellar nucleosynthesis

the creation of more massive nuclei from the fusion of less-massive nuclei inside stars. Just

about all of the elements heavier than helium on the Earth were originally created via stellar

nucleosynthesis.

stratosphere

layer of a planet's atmosphere above a troposphere where temperature rises with increasing

altitude because of the absorption of ultraviolet light.

subgiant

the stage in a star's life between the main sequence and the red giant stages. The helium core

shrinks and the hdyrogen shell layer outside the core undergoes nuclear fusion. The energy

of the shell burning is great enough to push the outer hydrogen layers outward and they cool

off. During the subgiant stage, the expansion is such that the luminosity remains essentially

constant as the outer layers expand.

sublime

the turning of a solid directly into a gas without going through the intermediate liquid phase,

e.g. the vapor of ``dry ice'' (the sublimation of frozen carbon dioxide).

sunspot

cooler region on the Sun's surface that is a region of intense magnetic fields and is associated

with solar activity. Because a sunspot is 1000 to 1500 K cooler, it is dimmer than the

surrounding surface. The number of sunspots is greater when the Sun is more active.

supercluster

a grouping of galaxy clusters pulled together by their mutual gravitational attraction to

produce long, thin structures up to a few hundred megaparsecs long with large voids devoid

of galaxies between the superclusters.

supergiant

a dying star of extremely high luminosity and relatively cool surface temperature. Their

diameters are over 100 times that of the Sun.

supernova

for Type II supernova: final huge mass-loss stage for a dying high-mass star where the outer

layers are ejected during the core's collapse to form a neutron star. A Type I supernova is the

result of enough hydrogen accreted onto a white dwarf's surface to put the white dwarf

beyond the Chandresekhar limit. The white dwarf collapses and the super-rapid fusion blows

the white dwarf apart (contrast with a nova). The luminosityof a supernova can temporarily

be as much as an entire galaxy of billions of stars.

synodic period

the time required for a planet or moon to go from a particular configuration with respect

to the Sun back to that same configuration (e.g., for the Moon, it is the time to go from a

given phase back to the same phase---29.5 days).

tangential velocity

the velocity perpendicular to the line of sight.

tectonics

any stretching or compression of the lithosphere.

telescope

device used to gather and focus electromagnetic radiation. A telescope extends the power of

human vision by making objects brighter, sharper, and larger, as well as, imaging objects in

wavelengths that are not detectable by the human eye.

temperature

a measure of the random motion energy (the average kinetic energy) of a group of particles

in a gas, liquid, or solid. The temperature is higher if the particles are moving faster.

theory

a logical, systematic set of principles or explanation that has undergone testing or validation

from careful observations and has stood up against attempts to prove it false. A scientific

theory can be used to make a variety of predictions of what will happen under different

circumstances.

thermal spectrum

a spectrum that has energy at all wavelengths (a full rainbow). Produced by solids, liquids,

and dense (high-pressure) gases.

thermosphere

upper layer a planet's atmosphere where the temperature rises with increasing altitude

because the gases absorb X-rays and ultraviolet light. X-rays ionize gas

particles. Aurorae occur in this layer.

time zone

interval of longitudes 15 degrees wide in which every clock is set to the same time (e.g.,

every clock in the Pacific time zone will give the same time).

total solar eclipse

a type of solar eclipse that happens when the Sun and Moon are exactly lined up and the

Moon is close enough to the Earth to totally block the Sun's surface (contrast with annular

eclipse).

transit technique

a method of finding exoplanets by looking for a drop in the brightness of a star as the planet

passes in front of the star.

trigonometric parallax

a method of determining distances to nearby stars that uses trigonometry to derive the

distance from the size of the parallax angle and the distance between a planet and the Sun:

distance in parsecs = (planet-Sun distance in A.U.)/(parallax angle in arc seconds).

tropical year

the time interval between two successive vernal equinoxes = 365.2422 mean solar days

(contrast with sidereal year).

troposphere

lowest layer of a planet's atmosphere (closest to the surface) where the temperature decreases

with increasing altitude and where convection is important. Clouds form in here. Greenhouse

effect is present.

T-Tauri (star)

young star that is just beginning nuclear fusion and produces strong outflows of particles

(winds) that clears away the gas and dust from which the star formed.

21-cm line radiation

emission line in the radio band by cool, neutral atomic hydrogen that is used to map the

structure of the Milky Way and other galaxies because it passes easily through dust in the

interstellar medium.

velocity

description of an object's motion that includes both its speed AND its direction of travel.

velocity dispersion

the spread of the distribution of the velocities.

vernal equinox

specific moment in the year (on March 21) when the Sun is directly on the celestial equator,

moving north of the celestial equator.

volcanism

any eruption of molten lava onto the surface.

wavelength

the distance between two crests or two troughs of a wave.

weather

the ever-changing combination of winds, clouds, temperature, and pressure at a particular

location and time. Short timescale description of an atmosphere in contrast to climate.

weight

amount of the force of gravity felt by an object. It is measured in units of newtons. It

depends on the strength of the surrounding gravity field.

white dwarf

the collapsed core for a dead low-mass star. The core is less than 1.4 solar masses and is

about the diameter of the Earth. The pressure from degenerate electrons prevents further

collapse.

Wien's law

relation between the wavelength of maximum emission in a thermal spectrum and its

temperature: wavelength peak in nanometers = 2.9 106/temperature in Kelvin.

zenith

point on the celestial sphere that is always directly above the observer regardless of his/her

location.

zodiac

narrow belt of twleve constellation centered on the ecliptic.

pdfcrowd.comopen in browser PRO version Are you a developer? Try out the HTML to PDF API

Astronomy/DSOsThe Astronomy DSO list specifies which Deep Sky Objects may be covered in the Astronomy event that year.

2014 DSOs2014 DSOs

Name Images Constellation Magnitude Distance Coordinates ExternalLinks

Mira(Omicron

Ceti)

Cetus

Apparent:2.0 to 10.1Absolute:~-2.5 to 4.7

~420 ly

RightAscension: 02h19m 20.70s;Declination: -02 58' 39.51"

ChandraNASAScienceNews

Mira is the prototype for Mira variables, which are red giants that oscillateover long periods. It is a binary star system, with Mira A the red giant thatis losing mass and Mira B the white dwarf that is accreting mass.

W49B

Aquila Apparent:~26,000lightyears

RightAscension: 19h11m 07sDeclination:+09 06' 00"

Chandra

W49B is an SNR that is theorized to have a distorted shape and a blackhole from the explosion that created the remnant. It may be the mostrecent black hole formed in the Milky Way.

Tycho's SNR(SN 1572)

CassiopeiaPeakApparent:-4

~9000 ly

RightAscension: 00h25m 17s;Declination:+64 08' 37"

ChandraNASAAPOD

A Type 1a supernova remnant that burst in early November 1572 and waslater studied by Tycho Brahe.

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Vela SNR

VelaApparent:12 ~800 ly

RightAscension: 08h35m 20.66sDeclination: -45 10' 35.2"

APOD

The closest known supernova remnant to us with a notable pulsar andneighboring nebulae. Contains NGC 2736 or the Pencil Nebula, which isthought to have formed from part of the shock wave of the Vela SNR

G1.9+0.3

Sagittarius Apparent:~28,000ly

RightAscension: 17h48m 45sDeclination: -27 10' 00"

ChandraNASA

Possibly the most recent supernovae, specifically Type Ia, in the MilkyWay. It has an extremely asymmetric pattern. Explosion was likely highlynon-uniform and unusually energetic.

Eta Carinae

CarinaApparent:-0.8 to 7.9 ~7,500 ly

RightAscension:10h45m 03.591sDeclination:5941 04.26

ChandraAPOD

A hypergiant with a smaller companion. Massive supernova, very bright. Ithas a chance of exploding at any time, and will be so bright that it rivalsthe moon.

SS CygniCygnus

Apparent:7.7-12.4 370 ly

RightAscension: 21h42m 42.804sDeclination: 4335' 09.88"

AAVSOChandra

A recurrent nova with a very massive white dwarf and a red dwarf-type starcooler than our sun. Often classified as U Geminorum type dwarf nova.

T Tauri

TaurusApparent:9.3-14 462 ly

RightAscension: 04h21m 59.43s;Declination:+19 32 06.42

NASAAPODUniverseToday

T Tauri is the prototype for T Tauri stars, which are the stars in the lifestage between protostar and main sequence. there is a nebula locatedclose to the star called Hind's Variable Nebula, which changes inluminosity as T Tauri varies.


GRS1915+105

Aquila Apparent: 40,000 ly

RightAscension: 19h15m 11.60sDeclination:+10 56' 44.00

Chandra

GRS 1915+105 is an x-ray binary star system containing a regular starand a black hole. It is one of the heaviest stellar black holes so far knownin the Milky Way and has a self-regulating black hole.

47 Tucanae

TucanaApparent:4.91 16,700 ly

RightAscension: 00h24m 05.67sDeclination: 72 04 52.6

ChandraAPODAPOD

47 Tucanae is the second brightest globular cluster after Omega Centauriand one of the most massive globular clusters in the galaxy.

TheTrapezium

OrionApparent:4 1,600 ly

RightAscension: 05h35.4mDeclination:05 27

ChandraAPODAPOD

The Trapezium is a relatively young open cluster in the heart o the OrionNebula.

T Pyxidis

PyxisApparent:6.4-15.5 15,600 ly

RightAscension: 09h04m 41.50sDeclination:32 22 47.5

AAVSONASAAPOD

T Pyxidis is a recurrent nova and nova remnant containing a sun-like starand a white dwarf. It is now close to the Chandrasekhar limit and mightsoon explode as a type 1a supernova.

Apparent:

RightAscension: 08h


Abell 30

CancerApparent:15.6 5,500 ly 46m 53.50s

Declination:+17 52' 45.40"

Chandra

Abell 30 is a planetary nebula in a special, rarely-seen phase of evolution.The evolution of A30 stalled and then started up again, so the planetarynebula was reborn.

RXJ0806.3+1527

(HM Cnc)

CancerApparent:21.1 ~1600 ly

RightAscension: 08h06m 23.20s;Declination:+15 27' 30.20"

ChandraSpace.com

An x-ray binary system composed of two white dwarves that are rapidlyorbiting each other. Their orbits are slowly getting closer, and the stars willeventually collide. Since they are faint, they are being observed by x-rayemissions.

V1647 Ori

Orion Apparent: 1,300 ly


ChandraNASA

V1647 Ori is a FU Orionis variable star, a low-mass protostar still partlysurrounded by its birth cloud. It is spinning as fast as it can without rippingitself to pieces.

V1

Andromeda Apparent:2.5million ly

RightAscension: 00h41m 27sDeclination: 00h41m 27s

HubblesiteNASA

A Cepheid variable star in the Andromeda galaxy that began Hubble'sdiscovery of the expansion of the universe by showing that the Andromedagalaxy was not part of our galaxy.

NGC 1846

DoradusApparent:11.3

~160,000ly


HubblesiteNASA

NGC 1846 is a globular cluster located in the outer halo of the LMC. The


most intriguing object is a faint green planetary nebula, and it doesn'tseem to belong in the cluster.

NGC 3132

VelaApparent:9.87 ~2,000 ly

RightAscension: 10h07m 01.7640sDeclination:40 26 11.060

APODAPOD

NGC 3132 is a planetary nebula. There are two stars in the nebula, one ofwhich is a white dwarf.

Previous Years' DSO Lists2013 DSOs

2012 DSOs

2011 DSOs

Basic note sheet for the 2011 DSOs, intended for use when asked to quickly identify things, or for those new to the event.

2010 DSOs

2009 DSOs

LinksBasic note sheet for the 2010-2011 DSOsSIMBAD Astronomy Database for DSOs

Category:Astronomy

This page was last modified on 3 January 2014, at 14:53. - This page has been accessed 25,058 times. - Disclaimers - About ScienceOlympiad Student Center Wiki

Formula Sheet

Intensity Ratio:

= 2.512

Magnitude Difference: = 2.5 log

Small Angle Formula:

=

Circular Velocity: =

Compare LGP:

=

Resolving Power: = .

()

Magnification: =

Wiens Law: =,,

=.

10

= .

Stefan-Boltzmann Law: = (//)

Doppler Formula:

=

Fusion Explained: =

Distance to Star: = ,

F Ratio: ()

()

M = mass of central body (kg) G = 6.67 10-11 m3/s2kg * Answer in m/s

D = diameter * Answer in times ()

D = diameter (cm) * Answer in arcseconds

FO = focal length of objective Fe = focal length of eyepiece

* Answer in nm

T = K = 5.67 10-8J/m2s degree4 * Answer in J

Vr = radial velocity = change in c = 300,000 km/s = observed

m = kg * Answer in Joules c = 3108m/s

p = parallax * Answer in AU

Distance Modulus: = 5 + 5 log = 10

=

Luminosity of Star:

=

Mass of Binary System: + =

Keplers 3rd Law: =

Mass-Luminosity Relation: = .

Life Expectancy: =

.

Schwarzschild Radius: =

Hubble Law: = Hd

Redshift: =

Age of Universe: =

10

Distance-Rate-Time: =

=

=

Newtons Law of Gravity: =

Keplers 1st Law (Eccentricity): =

Ratio:

/

Frequency: =

* Answer in times ()

M = solar masses p = orbital period (yrs) a = AU

p = orbital period (yrs) a = distance (AU)

M = star mass in MO * Answer in times ()

M = star mass in MO * Answer in O lifetimes 10 billion = years

G = 6.67 10-11 m3/s2kg M = mass (kg) C = 3 108 m/s * Answer in m

= velocity of recession of galaxy (km/s) H = 20km/s/Mpc d = distance (Mpc)

= change in O = unshifted

H = 70 km/s/Mpc * Answer in years

G = 6.67 10-11 m3/s2kg = masses of objects in kg r = distance between the two masses (m) F = the strength of the gravitational force (N)

Flux:

() =

=

()

Dispersion Distance: =

.

= 3.472 10

= 4.688 10

= 1.215 10

Diameter of orbit: 300,000 km * Answer in km

stnatsnoC

01 979594.1 = 1

562,602 = 1

01 876580.3 =

336162.3 =

01 35064.9 = 1

529799.2 = ,01

/) /( + )(01 76.6 = ,

01 679.5 =

461.873,6 =

01 989.1 =

01 9959.6 =

01 628.3 =

01 053.7 =

8371 =

01 25376.1 =

= )1( 11

06

= )"1( 11

06

01 5.4 = 000,000,1 = 1

1/5/13 Usef ul Formulas

1/12www.astro-tom.com/technical_data/usef ul_f ormulas.htm

ASTRONOMICAL FORMULAE

First, the important telescope formulas - i.e. The ones you should try to remember :-)

Magnification = Objective Focal Length / Eyepiece Focal Length

Example: A 2000 mm focal length telescope using a 20 mm eyepiece yields a

magnification of 100 times:

Example: Magnification = 2000 mm / 20 mm = 100

True Field of View = Eyepiece Apparent Field of View / Magnification of view

Example: If we are still using the 20 mm eyepiece from the previous example on the

same telescope, and we know from looking up in the manufacture's specifications that

the eyepiece has a 50 degree 'apparent field of view':

Example: True Field of View = 50 / 100 = 1/2 degree

In other words, the entire full Moon would just fit in the view since it is 1/2 degree

across, but you would see only the central portion of the Andromeda Galaxy which is

about 4 1/2 degrees across.

Time for a star to cross field:

The time in minutes that it would take a star at the celestial equator (DEC=0) to go

completely through the field of view when the telescope is not tracking, could be called

"T" The true field of view can then be calculated as

1/5/13 Usef ul Formulas

2/12www.astro-tom.com/technical_data/usef ul_f ormulas.htm

True Field of View = 4 * T

f/number = Objective Focal Length / Objective Diameter. Example: A 2000 mm focal

length telescope that has 200 mm (8 inch) diameter yields a value of f/10.

Exit pupil = Objective

important.pdf

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