STARS

The UniverseFormation of the UniverseHow do we study the formation of the universe?https://www.youtube.com/watch?v=QUpWCRadIIA

Solar Nebular Theoryhttp://www.universetoday.com/77525/nebular-theory/#ixzz2WBvmHTgK

EARLY ASTRONOMYAristotle and Ptolemy: Early AstronomersBelieved in the GEOCENTRIC Universe.

Sun and planets revolve around the Earth.

Roman Catholic Church agreed and declared it true.

Anybody against it was a HERETIC. MODERN ASTRONOMYCopernicus (1473 1543) and Galileo (1594 1642) Believed in a HELIOCENTRIC Universe.

Copernicus used his observations to discover the Sun Centered Universe.

He did not publish his findings until he was dying.

Galileo used his observations to support the Copernican theory.

He did not publish until very old and was put under HOUSE arrest as a heretic. MODERN ASTRONOMYJohannes Kepler: (1571 1630) Used precise observational tables to study planetary motion mathematically.Came up with the 3 Laws of Planetary Motion.

Keplers Laws supported the HelioCentric Universe.His evidence showed the orbits of planets to be ELLIPTICAL(oval) in shape.

The Universe from EarthWith the naked eye we can see about 2000 stars from Earth. The Milkyway is a band of light makingits way across thenight sky.What is it? It is ourview of our galaxy.

MilkywayNight Sky from EarthThe night sky is familiar, but few people look closely at what is going on.

Orion Constellation RisingNight Sky from EarthWhy do stars rise and set?What is important about the North Star?What are constellations?

Night Sky from EarthWhy do stars rise and set?The stars APPEAR to rise in the East and set in the West, just like the Sun. Reality . . . the Earth is ROTATING on its axis. More Reality . . . the stars stay STILL (relatively)Earth rotates about 1000mi/hrEarth Revolves around the Sun at 30km/sec

Night Sky from EarthWhat is the North Star?The North Star is just an AVERAGE star that happens to be nearly in-line with the Earths axis.Reality . . . It is NOT the brightest star.The name of the North Star is POLARIS.

POLARISConstellationsConstellations are groups of stars that make up mythological pictures. There are 88 official constellationsThey represent REGIONS of the skyThere are two kinds of Constellation Groups.Circumpolar ConstellationsLocated close to North Star and can be seen all year.Seasonal ConstellationsFarther from North Star so only can be seen for short periods of time. (seasonally)Caused by Earths REVOLUTION around the Sun.

Circumpolar Constellations5 Constellations can be seen all year round from the Northern Hemisphere.Ursa Major (Big Dipper)Ursa Minor (Little Dipper)Cepheus (the King)Cassiopeia (the Queen)Draco (the Dragon)

Finding NorthHow to find North.Find the Big Dipper.Follow the two end Pointer stars to Polaris.

SEASONAL CONSTELLATIONSSeasonal Constellations Constellations that APPEAR to rise in the East and set in the West throughout the year.

The constellations that are visible change as Earth revolves around the Sun.

Example: Orion

Winter Circle Constellations

Spring Constellations

So what are you looking at?What are you ACTUALLY SEEING?

LIGHTWHAT IS LIGHT?Light is really just the visible part of electromagnetic radiation produced by stars like our Sun. . . OKAY. . . Then what is electromagnetic radiation?

Electromagnetic RadiationDefinition: Energy that is radiated in waves and is emitted by all objects like stars including our Sun.Best known as VISIBLE LIGHT but includes radio waves and ultraviolet waves too.

Rainbows May Include Very Unusual eXamples of GreenLight and EM RadiationElectromagnetic Radiation can travel through empty space (without molecules).They travel as vibrations in electrical and magnetic fieldsAll forms of EM radiation travel at the SAME SPEED. Speed of Light = 300,000 Km/secSpeed of Sound = 340 m/sec (.340 km/sec)

Click here Animation: Interaction of vibrating chargesLight as WavesA wave is just a disturbance in some medium (water, air, space)

A wave travels through a medium but does not transport material

A wave can carry both energy and information

Wave TerminologyWavelength - distance from peak of one wave to peak of another.Amplitude - the height of the wave compared to undisturbed state. Think volume with sound waves and brightness with lightFrequency - the number of waves passing in a given amount of time

Wave TerminologyHow do these terms relate to one another?As wavelength DECREASES . . . FrequencyEnergyDanger

IncreasesIncreasesIncreasesElectromagnetic Spectrum

Electromagnetic Spectrumname for the range of electromagnetic waves when placed in order of increasing frequency Click here (AnimationSize of EMwaves)The Electromagnetic SpectrumHuman eyes see the visible part of the spectrum

Longer wavelengths includes infrared light, microwaves, and radio

Shorter wavelengths includes ultraviolet light, X-rays, and gamma rays

All of these travel at the speed of light.

But, they have different wavelengths.

Wavelengths of Light - VisibleWe break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)Red is the LONGESTViolet is the SHORTEST

Visible light is the Smallest section of the EM Spectrum

Astronomers use different wavelengths of light to study objects in space because:

We get a different view and lots more information.

Some objects are only visible at certain wavelengths

The Sun at Different Wavelengths

VisibleUltravioletX-rayX-rayTELESCOPESOptical Telescope: Used to see VISIBLE light from objects in space.Galileo: designed small 30X scope Observed the moon and began the modern age of Astronomy

Optical TelescopesRefracting telescopeobjective lens bends lightReflecting objective mirror reflects light

Refracting Reflecting Objective lensObjective mirrorProblems with Earth-based telescopesEarths atmosphere reflectsx-rays gamma rays most UV raysEarths atmosphere blurs imagesAtmosphere bends light.twinkling of stars (Caused by movement of air)Light pollution caused by man-made lightSolution? Put the telescope in space.Advantages of Space TelescopesCan collect EM wavelengths that do not penetrate the Earths atmosphereGamma raysX-raysMost Ultraviolet waves

Can collect all EM radiation without disruption from Earths atmosphereImages MUCH sharperDisadvantages of space-based telescopesExpensive to launch and maintainDifficult to repairShort lifetimeHUBBLE SPACE TELESCOPELaunched in 1990Mirror error fixed 9315 yr life expectancyGoing on year 23!!96 minutes for 1 orbit around Earth

HUBBLE IMAGES

SPECTROSCOPY-CompositionSpectroscopy: Study of Star Spectrums.Can be used to determine:COMPOSITION of a starTEMPERATURE of star DIRECTION OF MOTION of starTypes of Spectrums:

Incandescent BulbFluorescent BulbSun and StarsBright Line SpectrumDark Line SpectrumContinuous Line SpectrumSPECTROSCOPY - CompositionSpectral LinesEach element has its own set of Spectral Lines.

We call them Fingerprints because each is different.

Fluorescent Light SpectrumSPECTROSCOPY- CompositionChemical Composition Study Star lightSpectroscopy :Studying the spectrum of a star. Comparing spectrums of known elements to the spectrum of a star to determine what elements are in it.In general stars are 75% H and 24% He and 1% or less everything else - but we can still do it pretty well

SPECTROSCOPY - TemperatureSpectroscopyHow do you determine TEMPERATURE of a star?By looking at the color of the starBy looking at the stellar spectrumWhat color indicates HOT?Blue = HotRed = CoolWhich stars are hottest and which are coolest in image?

Top ones HOTTER, bottom ones COOLERSpectral Lab SummaryLooking at these stellar spectrums, what properties of the star can you tell us?What wavelength it produces the mostIts approximate temperatureWhat color it will appear

BlueGreenYellowRedHotCoolSPECTROSCOPY - Motion

Doppler Effect:The apparent lengthening or shortening of wavelengths due to motion.Sound waves: MotionTowards = shorter waves = HIGHER pitchAway = longer waves = LOWER pitchLight wavesTowards = shift to BlueAway = shift to Red

Doppler Effect https://www.youtube.com/watch?v=Djz_rtnXSfYhttps://www.youtube.com/watch?v=yWIMWqkcRDU&feature=relatedhttps://www.youtube.com/watch?v=Tn35SB1_NYI

https://www.youtube.com/watch?v=Bx0SMevn-0c

SPECTROSCOPY - MotionMotion of StarsIs a star moving TOWARDS us or AWAY from us?How can we tell?Spectroscopy: Studying star spectrum tells us direction of motionMoving AWAYSpectral lines of a star shift towards the RED end of the spectrum.Called RED SHIFTMoving TOWARDS Spectral lines of a star shift towards the BLUE end of the spectrum.Called BLUE SHIFTSPECTROSCOPY - MotionRed Shift Star moving AWAY.Wavelengths LENGTHEN.Spectral lines of star shift towards the RED end.Blue ShiftStar moving TOWARDS.Wavelengths SHORTEN.Spectral lines of star shift towards the BLUE end.

PROPERTIES OF STARSThere are 4 properties of a star that we measure.DistanceChemical CompositionTemperatureMagnitude

Measured in Lightyears (ly) = the distance light travels in one year = 1.0 x 1013 km.The elements that make up the star.The actual brightness of the star or its appearance of brightness.How HOT is it??BRIGHTNESS OF STARSMagnitude of starsThe amount of light a star gives off. (How BRIGHT it is)Absolute MagnitudeThe actual brightness of a star if a standard distance from Earth. Apparent MagnitudeThe brightness of a star as seen from the Earth.Factors:DistanceSizeAbsolute magnitude

BRIGHTNESS OF STARS

INVERSE SQUARE LAW of LIGHTAs light travels farther, it becomes more spread out, so there is LESS light per UNIT 2 .

Farther away = Less light reaching EarthBRIGHTNESS OF STARSThe Magnitude Scale:Ancient Greek put stars in 6 groups. 1st group = brightest6th group = dimmest

The magnitude scale is based on that system.Magnitude 1 = brightestMagnitude 6 = dimmer

BRIGHTNESS OF STARSMore numbers had to be added for brighter things.What did they do?Go NEGATIVEExamples of Apparent magnitudes:Sun-26.8Full moon-12.6Sirius -1.4The SMALLER or MORE NEGATIVE the number = BRIGHTERhttps://www.youtube.com/watch?v=9P8Veb_AlJ0

DISTANCEDetermining Distance of StarsMethod: PARALLAX the apparent shift of an object when viewed from two different locations. You can determine distance by measuring the angle of an object from the ends of the baseline of a triangle.

DISTANCE

ParallaxUseful only for fairly close stars.Needs a measurable Parallax angle = LONG BASELINELargest baseline isDIAMETER of Earthsorbit.

Putting it all togetherHow do we effectively compare so many properties?What are the most useful properties to measure?Can we see patterns?The tool we will use is called the Hertzsprung-Russell diagram (H-R diagram)

MagnitudeAn H-R diagram plots:absolute magnitude temperature of stars.TemperatureMain SequenceSuper Giants and Giants

Most stars (90%) fall somewhere in the main-sequence part of the H-R diagram. What is the relationship of Temperature to Magnitude for these stars?The Hotter the Brighter

MagnitudeTemperature (K)Stars with lower T and higher M than main-sequence stars must have LARGER radii (Size):

giants and supergiantsCompare Proxima Centauri to Betelgeuse.How the same?How different?Why do you think that is?

MagnitudeTemperature (K)Stars with higher T and lower M than main-sequence stars must have SMALLER radii (Size):

white dwarfsCompare Sirius B to Bellatrix.How the same?How different?Why do you think that is? The MASS of a main-sequence star determines its MAGNITUDE and SPECTRAL TYPE!O = High MassF = Medium MassR = Low mass

MagnitudeTemperature (K) SPECTRAL CLASS is determined by the stars TEMPERATURE.

O B A F G K M

Therefore COLOR can tell SPECTRAL CLASS.O = Blue M = Red

What do you think the Mass of the Sun is?MEDIUM