earth in space topic 3 in review book i. celestial observations all of the objects in our sky appear...
TRANSCRIPT
Earth in space
Topic 3
in Review Book
I. Celestial observations
All of the objects in our sky appear to be located on a dome (hemisphere) that encircles the earth
This dome is referred to as the
celestial sphere
a. General Terms
1. The horizon:
the imaginary line where the earth appears to meet the celestial sphere
2. The zenith:
the point on the celestial sphere directly above an observer…
90º above the horizon
3. Altitude: a vertical angle…the angular distance above the horizon
4. Declination: celestial lines of latitudeThe celestial equator is the reference point+ declination = north- declination = south
5. Azimuth: a horizontal angle:the angular distance measured clockwise from due north.
6. Right Ascension: celestial lines of longitude
Right ascension is labeled in units of time…
it is given in hours (h), minutes (m) and seconds (s)
and ranges from 0h 0m 0s to
24h 0m 0s
7. Constellations: groups of stars that appear to form a pattern in the sky
a. Some stars and constellations are circumpolar…they seem to move in circles around Polaris…when photographed, they create circular star trails
Circumpolar motion occurs because Polaris is directly above our axis of rotation.
The farther north an observer is located, the greater the number of circumpolar stars
Circumpolar motion
b. Stars/constellations change their position in the sky nightly due to the rotation of the earth and…
c. seasonally because of the revolution of the earth
We’ll talk more about these motions in the next unit…so stay tuned!
d. Some Constellations you should know:
i. The Big and Little Dippers:Seen on the horizon in the fall
at the zenith in the springThe B.D. contains the pointer
stars to Polaris
ii. Orion: We only see it in the
winter during “prime time” viewing
iii. Summer Triangle: We only see it in the
summer during “prime time” viewing
B. Origin of the universeThe Big Bang theory:There is scientific evidence
that supports that
approximately 14 billion years ago, the universe was a dense concentration of matter that
expanded explosively…
At this time:
all matter and space was created and moved outward in all directions at the speed of light (300 million m/sec),
masses of gas cooled and condensed and…
stellar systems formed. Evidence of the Big Bang
includes:
1. The uniform age of all of the galaxies
2. Weak electromagnetic radiation from the explosion (cosmic background radiation) has been detected
C. The fate of the universe
In 1929, Edwin Hubble examined the spectra of distant galaxies
He compared the spectral lines of far away galaxies to those of nearby stars
Hubble knew that when a light source is moving away from an observer it’s wavelength becomes longer…This results in a shift of its spectrum towards the red endconversely, when a light source moves towards an observer, there is a shift towards the blue end of the spectrum
He found that the nearby stars had spectral lines similar to those expected.
But he found that the distant galaxies showed spectral lines shifted to the red end of the spectrum
The shift towards the red end of the spectrum indicated that distant galaxies are moving away from the earth…
If the shift had been towards the blue end of the spectrum, the galaxies would be moving towards the earth
Hubble’s law
Galaxies are retreating from us at a speed proportional to their distance from us
The expanding universe theory
proposes that the universe is expanding so that objects (galaxies) move away from one another
The galaxies aren’t expanding…just the spaces between them
D. Classification of stars
Stars are classified based on spectral analysis of their light
This information is organized on a chart called aHertzsprung-Russell diagram
See ESRT page 15
The H-R diagram is based upon the relationship between the luminosity (brightness) of a star and its temperature
In general…hot stars tend to be blue/white and bright…cool stars tend to be red/yellow and not as bright
When a star varies from this generalization, an inference can be made regarding where it is in its life cycle
E. The Life of A Star
Stars begin as clouds of gas or dust that gets pulled together by a developing force of gravity. As the force of gravity builds, and the star becomes hotter, fusion begins to take place.
Fusion creates an outward force that is in opposition to the inward pull of gravity.
These forces, and how balanced they are, determine the life of a star.
Smaller stars last longer than massive stars…
Bigger stars are hotter and undergo fusion much faster … therefore, the balance between the forces is upset sooner.
Once fuel begins to diminish,
the equilibrium
Is disrupted
F. Distances to Stars
The sun is the closest star to earth
It is 150,000,000 km awayThis distance is equal to
1 Astronomical Unit (AU)
The next nearest star is
Alpha Centauri
It is ~ 40 trillion km away
This would be ~ 266,666 AU
To make stellar distances more manageable, we convert distances to light years
This is the distance light travels in one year!!!
Light travels 9.5x1012 km/yearWhich is 9,500,000,000,000
(9.5 trillion) km/year Alpha Centauri is 4.35 ly from
Earth
It takes the light from the sun
8 minutes and 20 seconds to reach Earth
Another unit of distance is a parsec
Parsec stands for
1 second of parallax
Parallax is the apparent shift in the position of one star in relationship to another star
This is equal to 3.26 ly
G. Stellar Brightness
1. Luminosity is the actual (true) brightness of a star
This is dependent upon
size:
the larger the star, the more luminous it tends to be
and temperature:
The hotter the star, the more luminous it tends to be
2. Apparent magnitude is how bright a star appears to an observer on Earth
This is influenced by the distance between a star and the observer
As distance increases,
the apparent brightness decreases
This is reported as a numerical value:
Brighter stars have lower apparent magnitudes.
Apparent magnitude can be reported in negative numbers
A star with an apparent magnitude of 6 is the faintest that can be seen with an unaided eye
3. Absolute magnitude is the brightness a star would have if it was located 32.6 ly from Earth
This eliminates the effect that distance has on the apparent magnitude of a star
This is a comparative brightness and can be used to determine the relative distances between stars and the earth.
H. Galaxies and the Universe
A galaxy is a system that contains billions of stars
There are at least a billion billion galaxies in our universe
The sun is located in the Milky Way galaxy
and is only one star among 100 billion stars!
Neighboring Galaxies
Magellanic Clouds
the closest galaxies
They are only visible from the Southern Hemisphere
Andromeda Galaxy
the closest galaxy visible from the Northern Hemisphere
1. Types of galaxiesGalaxies are classified based
upon their shape Spiral galaxies:
consist of a central nucleus with “arms” that trail behind while the galaxy rotatesThe Milky Way is a spiral galaxy
100,000 ly across
ii. Elliptical galaxies:range in shape from nearly spherical to lens shaped
iii. Irregular galaxies:do not have any specific shape.The stars are spread unevenly throughout the galaxy
II. Our solar systemConsists of:
1 star
8 planets
61 (and counting) natural satellites
thousands of asteroids
millions of meteoroids
numerous comets
Which all travel through space in paths called orbits that are
ellipses with the sun at one of the foci
a. Models of the universe
1. Geocentric model:Earth-centeredProposes that the earth is stationary at the center of the universe
and all of the celestial objects (sun, moon, planets, stars) revolve around it.
2. Heliocentric modelSun-centeredIn 1543, Copernicus published a paper proposing that the sun was stationary and everything revolved around it.Galileo supported this theory through telescopic observations
3. Evidence of heliocentrism
a. Circumpolar motion of stars:provides evidence of the earth’s rotation.If the earth did not rotate, star trails would not be created
b. Foucault pendulum:Also provides evidence of the earth’s rotation.Jean Foucault created a free-swinging pendulum that knocked down standing pegs which led to his conclusion that the earth rotates
Foucault Pendulum
Foucault pendulum 2
c. Coriolis Effect
The deflection of a free-moving substance to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to the rotation of the earth
d. Retrograde motion:
The apparent backwards motion of a planet against the backdrop of stars.
This is due to the variations in rates of revolution
III. Orbital geometry
A. Kepler’s laws of planetary motion describe the motions of the planets in their orbits around the sun.
1. First law
The planets move in orbit around the sun in a path that is an ellipse with the sun at one of the foci
An ellipse is a closed curve that ranges in shape from a perfect circle to a straight line.
Eccentricity is a measure of the “out-of-roundness” of an ellipseIt ranges in value from 0 (perfect circle) to 1 (straight line)
As the distance between the foci increases, eccentricity increases and the ellipse becomes more oval
Length of the major axis
Distance between the foci
Now you try!
f f
3.7 cm
9.2 cm
Calculate eccentricity:
E = dbf
lmaE = 3.7 cm
9.2 cmE = 0.40
2. Second law
An imaginary line joining the planet to the sun will sweep out equal areas in equal amounts of time
Since the orbit of each planet is an ellipse with some degree of eccentricity,the distance between the planet and the sun will vary throughout its revolution
Kepler’s law says that the areas covered each day by the planet will be the same, but the distance traveled will differ
This results in variations in the velocity of revolution
When the planet is closer to the sun,the distance to travel is greater,so the velocity has to be greater
When the planet is farther from the sun,
the distance to travel is less,
so the velocity is less
In summary
Orbital velocity isGreatest when the planet is
closest to the sun
andleast when the planet is
farthest from the sun
A C
B
D
A = perihelion = closest to the sunC = aphelion = farthest from the sun
3. Third law
A planet’s period of revolution is directly related to its distance from the sun
as distance from the sun increases
period of revolution increases
This difference in rate of revolution results inretrograde motionwhich is seen when the earth passes a planet farther from it causing it to look like it is going backwards
B. Gravitational attraction
Sir Isaac Newton statedEvery object in the universe
is attracted to every other object in the universe.
This attraction is called gravity
Force of gravity α m1 m2
d2
Changing distance would have the greatest effect on gravity
Increasing massIncreases gravityIncreasing distanceDecreases gravity
