1. Unit 9: Astronomy Notes

2. The Solar System In the Old Days… This was called the GEOCENTRIC MODEL
People thought Earth was in the center
Celestial objects revolved around Earth
This was called the GEOCENTRIC MODEL
Observations raised doubt
about this model…
And it was gradually
replaced with a new idea!

3. Heliocentric Model Planets revolve around the SUN This model explains
Mercury is closest
Planets move in
elliptical orbits
-Moon revolves
around Earth
This model explains
all motions of celestial
Bodies!
Don’t Forget: Our Solar
System is 4.6 billion years old!

4. The Inner Planets…
Small, dense, made of rock

5. The Outer Planets…
Large, low density, made of gas

6. Sun and 8 planets (plus Pluto) and other stuff
Solar System…
Sun and 8 planets (plus Pluto) and other stuff
The Sun is a “medium” sized yellow star
The Sun contains
> 99% of solar system mass

7. “I’m sorry Pluto, you’re just not big enough”

8. Sun with Other Yellow Stars…
Sun is really not that big!

9. Sun with Red Giant Stars…
Sun is pretty darn small!

10. Asteroids! Large Rocks too small to be planets
Can be up to 1000km wide!
Mostly in the Belt between Mars and Jupiter

11. Comets! Dirty snowballs Really LONG ORBITS Very Eccentric Orbits
Come from the Kuiper Belt/Oort clooud
Comet Hale-Bopp, 1997

12. Meteors!
Streak of light from a meteoroid going through Earth’s atmosphere
Meteoroid is a boulder sized rock in space
Meteorite is left over rock that hits Earth

13. Beyond the Solar System…GALAXIES
Billions of stars! Home: The Milky Way
Contain other solar systems too!
Come in spiral, ring, and sombrero shapes

14. Beyond the Solar System…UNIVERSE
Lots of SPACE
Billions of GALAXIES
EVERYTHING there IS!
In order from smallest to largest…
Planet (smallest)
Star
Solar System (one star, several planets)
Galaxy (many solar systems and stars)
Universe!

15. The Expanding Universe
Red Shifts (also called Doppler effect)
Refers to perceived change in wavelength of a wave that is emitted from a source that is moving away or toward an object
Proves Earth and the source are moving away from each other.
Moves toward – higher pitch
Moves away- lower pitch
Occurs for light and sound

16. The Expanding Universe
(Doppler Effect video)

17. The Expanding Universe
Hubble’s law
Galaxies are retreating from the Milky Way at a speed that is proportional to their distance.
Evidence red shift of distant galaxies
As time passes the galaxies move farther apart just like rising bread.

18. The Big Bang Big Bang Theory
States that at one time, the entire universe was confined to a dense, hot, supermassive ball.
Then about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions.

19. Kepler’s Laws Describes the motion of planet’s orbits around the Sun.
Planet’s move around the Sun in ellipses, with the Sun at one focus.
The line connecting the Sun to a planet sweeps equals areas in equal times.
The square of the orbital period of a planet is proportional to the cube of the mean distance from the Sun. (Half the sum of smallest and greatest distance from the Sun)

20. Kepler’s Law

21. Precession, Nutation, & Barycenter
Change in direction of axis without a change in the tilt.
Impacts position of stars, but doesn’t change the seasons.
26,000 year period

22. Precession, Nutation, & Barycenter
Wobbling around the axis.
Occurs over a 18 year period

23. Precession, Nutation, & Barycenter
Point between 2 objects that balance each other

24. Precession, Nutation, & Barycenter
Sun moves as the planets tug on it.
Sun orbits the solar system’s barycenter.
Never strays too far from the barycenter.

25. Why does the Moon have Phases?
Moon has phases because it orbits the Earth, which causes the portion we see illuminated to change.
Moon phases are determined by the placement of the Moon, Earth, and Sun.
Moon take 27.3 days to orbit Earth
Lunar Phase Cycle (New Moon to New Moon) is 29.5 days