Unit 9: Astronomy Notes

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!

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!

The Inner Planets… Small, dense, made of rock

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

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

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

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

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

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

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

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

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

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!

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

The Expanding Universe http://www.sciencechannel.com/video-topics/space-videos/time-doppler-effect/ (Doppler Effect video)

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.

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.

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)

Kepler’s Law

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

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

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

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.

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