Astronomy 105 Homework #1

Due February 1^st, 2008

The celestial equator is the projection of the Earth's equator (latitude = 0^o) onto the celestial sphere (see page 41). It divides the sky in to two regions: northern and southern hemispheres. The angular distance from the celestial equator to the north celestial pole (to Polaris, the pole star) is 90^o. This set-up is shown in the drawing below.

1) Can someone at the South Pole (or anywhere in the southern hemisphere) see Polaris? (2 pts)

2) What is the elevation angle of Polaris if you a) lived on the equator, b) lived at the north pole, and c) lived at a latitude of 45^o north. (6 pts)

The zenith is the point in the sky straight overhead, that is the point in the sky that always has an elevation angle of 90^o. The angle between the zenith and the celestial equator is exactly equal to your latitude. So the elevation of the celestial equator on the meridian is simply 90^o - Latitude.

3) We live in Las Cruces, with a latitude of 32.5^o. What is the elevation angle of the celestial equator at the meridian? (5 pts)

4) There are 360 degrees in a circle, and in Longitude. Since the Earth rotates once in 24 hours (our day), every hour the Earth rotates 15^o. The longitude of Las Cruces is 106.7^o, where 0^o is defined to be Greenwich (near London) England. How many hours difference are there between Las Cruces and Greenwich? (5 pts)

5) The longitude of New York City is 71.9^o, how many hours (round your numbers) are there between New York City and Las Cruces?

Thus, when it is 4pm EST in New York City it is ____________ MST in Las Cruces. (7pts)