Name: Partner(s): Day/Time: Version: Planetarium

# Coordinate Systems in the Planetarium

## Part 1: alt-az

Your GSI will set the planetarium to display the stars tonight at 8 PM and point out a star to watch north of the equator. Record the star's name as well as the altitude and azimuth for position 1 in table 1. Note that the scale in the planetarium is different from the scale in the real world, so you'll need to measure with your hand then compare that to the degree markings on the meridian scale.
Your GSI will move the projector until the star transits the meridian. Record the altitude and azimuth under position 2 for the first star.
Your GSI will again move the planetarium back to 8 PM and point out a star south of the equator to watch. Record its name and the altitude and azimuth for position 1 in table 1. Your GSI will move the planetarium again until the second star transits. Record the altitude and azimuth for position 2 for this second star.

Table 1: Alt-Az positions
 Star name Pos'n Altitude (deg) Azimuth (deg) 1 2 1 2
1. Does the altitude of most of the stars remain constant or change throughout the night?  Does the azimuth?

2. What are the coordinates of Polaris? Do these coordinates change?

## Part 2: RA and dec

Now you will observe the same 2 stars just like you did in part 1, but this time measure their Right Ascension and declination. You'll have to estimate the declination like you did the altitude, but measure distance from the equator! Record your results in table 2.

Table 2: RA and dec
 Star name Position RA (hours) Dec (degrees) 1 2 1 2
1. Does the RA of most of the stars remain constant or change throughout the night? Does the dec?

2. What are the coordinates of Polaris?

3. What is the declination at the northern horizon?