The Andromeda galaxy lies about 2.5 million light-years away. To what distance do the angular  resolutions of SST (3”), HST (0.05”), and a radio interferometer (0.001”) correspond at that distance?

Which of the following statements does not use the term light-year in an appropriate way?
A) A light-year is about 10 trillion kilometers.
B) It's about 4 light-years from here to Alpha Centauri.
C) It will take the Voyager spacecraft about 20,000 years to travel just 1 light-year.
D) The Milky Way Galaxy is about 100,000 light-years in diameter.
E) It will take me light-years to complete this homework assignment.

Given that earth orbits at 150000000 km from the sun through what distance does earth move in second? an hour? a day?

How long does it takes for the moon to move a distance equal to its own diameter of angular 0.5?