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the branch of physics that studies celestial bodies and the universe as a whole.

The Scale of the Universe

Local Group
Solar Systems and Star
Sun and Planets

1 light year

measurement = to the distance traveled in a vacuum at the speed of light for 1 year. (approx 9.5 trillion km)


-1 billion light years across
-mostly empty space
-contains billions of . . .


-120 mill. light years across
-contains dozens of . . .

Local Group

-5 mil. LY across
-contains about 30 . . .


100,000 LY across
o contains billions of stars
o Our galaxy: Milky Way (200 bill. stars)

Solar System

Contains planets orbiting the sun.

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