Homework 3: Due Monday, February 16

1. Where on Earth would you have to be for the celestial equator to pass through your zenith? You would be at the equator.
   Where would you be if the celestial equator lay on your horizon?
   You would be at the North or South Pole.
   Where would you be if the North Celestial Pole was at the zenith?
   You would be at the North Pole.
2. At what time does the star Betelgeuse (in Orion) transit as viewed from Northfield on February 14?
   It transits at 8:30 P.M.
   What is its altitude at the time that it transits?
   52 degrees 28 minutes.
   What is the declination of Betelgeuse?
   7 degrees 24 minutes.
   Does the altitude of Beltelgeuse change over the course of the night?
   Yes it does--the altitude changes as Betelgeuse rises and sets.
   Does the declination of Betelgeuse change over the night?
   No it doesn't--the right ascension and declination of a star are fixed on the celestial sphere. How many times a night does Betelgeuse transit?
   It transits once.
   Does the altitude of Betelgeuse at the time of transit depend on the date?
   No--Betelgeuse has the same motion with repect to the horizon night after night. The motion doesn't change but the time at which it occurs does. (In fact, the motion is repeated 4 minutes earlier each night).
   Explain your answers. Use your Starry Nights software and your star maps to answer this question.
3. Now look at the nightly motion of the star Alnitak (the leftmost star in the belt of Orion), again using your Starry Nights software. Where does Alnitak rise (give a compass direction here)? It rises in the east.
   Where does it set?
   It sets due west.
   Does your answer depend on the date?
   Just like Betelgeuse, it has the same motion every night. That motion just occurs 4 minutes earlier each night.
   Does your answer depend on your location on the earth?
   Nope--all stars that lie on the celestial equator rise in the east and set in the west independent of where the observer is.
   What is the declination of stars that rise due east and set due west?
   They lie on the celestial equator so they have declination 0 degrees.
4. On the Starry Nights menu select Guides: Celestial Grid, then fill in the blanks. Stars with a declination between 45 degrees 30 minutes and 90 degrees are circumpolar when viewed from Northfield.