**Problem
Set #1**

**ASTR 3830**

** **

- 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?

- 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 A
_{v}is 2 magnitudes?

- 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?

- 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?

- 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?

- 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?

- 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 H
_{0}to make this offset insignificant?