21 Sep 2000ASTR103, GMU, Dr. Correll1 Build Your Foundation II.

21 Sep 2000 ASTR103, GMU, Dr. Correll 1

Build Your Foundation IIBuild Your Foundation II

21 Sep 2000 ASTR103, Sec 3, GMU, Dr. Correll 2

The Solar SystemThe Solar System

• How many stars are there in the solar system?• Was the solar system created as a direct result

of the birth of the universe?• How long has the Earth existed?• Is Pluto the farthest planet from the sun?• What typical shapes do moons have?



• The solar system formed from an interstellar cloud of gas and dust--the solar nebula – Mostly hydrogen and

helium (created in the big bang)

– Also contain heavier elements--silicates, iron, etc (created in larger stars)



• Solar nebula contracts– flattens and spins– Sun begins to

shine– gas expelled from

inner disk by solar radiation

– ice and dust accrete to form planetesimals (~10 km in size) and then planets



• Computer simulations show formation of inner solar system takes as little as 150 million years--only about 1/30 the age of the solar system



• Stellar nebula seen in other star formation regions



• Thought experiment:– If I’m looking at a star with one large planet in orbit

around the star, what kind of motions do I see?• Remember Newton’s 3rd law of motion--for every action

there is an equal and opposite reaction– If planet is very tiny?– If planet is very large?



• Thought experiment:– OK, so I see both the star and the planet circling each

other (or more accurately, there common center of gravity)

– If I’m looking at the light from the Star, using a spectroscope, what do I notice about the absorption and emission lines?



• Thought experiment:– Right, I’ll see the absorption/emission lines Doppler

shifted. From this I can measure relative velocities.– From the velocities and periods of orbits, I can calculate

the masses of the star AND the planet!


The Solar SystemThe Solar System• How many stars are there in the solar system?

– One, our Sun.

• Was the solar system created as a direct result of the birth of the universe?– No, the universe was created 13-18 Billions years ago; the

solar system is about 4.6 Billion years old

• How long has the Earth existed?– About 4.6 Billion years old

• Is Pluto the farthest planet from the sun?– Sometimes Neptune is

• What typical shapes do moons have?– Irregular spheroids, e.g.--potatos

21 Sep 2000ASTR103, GMU, Dr. Correll1 Build Your Foundation II.

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