Problem Set #1

ASTR 3830

1. HST (Hubble Space Telescope) records images with 0.1” resolution. Each stellar position can be centroided to about 10% accuracy. At what distance can HST measure a distance to 10% accuracy? How well can it measure at the ecliptic pole? Voyager carries a telescope with 2” resolution and 10% centroiding. At what distance from the Sun could it match HST?

1. You measure a signal of 200c/s in B, and 1000c/s in V. What is B-V?  What is the spectral type if there is no reddening?  What is the spectral type if Av is 2 magnitudes?

1. You make an HR diagram for a cluster and find the main sequence turnoff is near spectral type A1.  About how old is the cluster?

1. You take multiple images of a galaxy and detect a star of magnitude 27 varying with a period of 50 days. How far away is the galaxy?

1. You detect the Lyman a emission line (1216Å) from a distant galaxy at 1425Å. How fast is the galaxy receding?  Calculate values for z and cz.  What is its distance?

1. If there is no acceleration or deceleration, then the inverse of the Hubble constant is the age of the universe. If the Hubble constant were 55km/s/Mpc then how old would the universe be?  What about 75km/s/Mpc, and 110km/s/Mpc?  Hubble first estimated 500km/s/Mpc.  What is the problem with this number?

1. The Milky Way is traveling about 400km/s relative the Hubble flow (the term for the average of the universe).  How far way must you calibrate the H0 to make this offset insignificant?