5. Politely remind this person that the celestial sphere is not real, so you can't go there. However, it is a useful model of the heavens, because the stars do appear to be equally distant from the Earth, and the Earth's rotation does make the stars appear to move as if they were attached to a vast sphere.

7. The celestial equator divides the celestial sphere into northern and southern hemispheres. Each point of the celestial equator lies directly above a corresponding point on the Earth's equator. If the Earth's axis of rotation is extended away from the Earth (in both directions) until it touches the celestial sphere, then the resulting two points of contact are the north and south celestial poles. If you were on the Earth's equator, the celestial equator would pass directly overhead (that is, through your zenith) -- see Fig. 2-9 to convince yourself of this.

23. On page 25, your textbook states, "If you follow a particular star on successive evenings, you will find that it rises approximately 4 minutes earlier each night...." So if Mintaka rises at 11:00 PM on Nov. 1, then on Nov. 8 (seven days later), it will rise approximately 7 x 4 = 28 minutes earlier, at 10:32 PM.

25. In the picture below, Figure 2-5 has been extended to include the rest of the Earth's orbit. May is two months (or 1/6 of a year) earlier than July, so the blue disk at the bottom-left (1/6 of the orbit clockwise from the July position) is where the Earth would be in May. The time for the red stick-figure is midnight (since he's on the opposite side of the Earth from the Sun). It's clear that the stick-figure cannot see Perseus (the constellation at the upper-right) from this position, since the Earth is blocking his view. (For that matter, he can't see Perseus at any time in May, since the Sun is between the Earth and Perseus at that time.)

26. Every 3 hours (which is 1/8 of a 24-hour day), the stars rotate 1/8 of a circle counterclockwise. So at 9 PM, the Dippers will be positioned 1/8 of a circle clockwise from their midnight positions; and at 3 AM, they will be located 1/8 of a circle counterclockwise from where they were at midnight. See the picture below.

28. b) In the picture below, I've reproduced Fig. 2-11, highlighting one of the star-trails in red. (The celestial pole is where the black lines cross.) I'd say the star-trail is about 5/12 of a circle, so the camera shutter must have been open for about 5/12 of a day, or 10 hours out of 24.

Adapted from Fig. 2-11, (c) Anglo-Australian Observatory, photo by David Malin

Last edited 29 Jan 04 M. A. Weinstein.