Astronomy Question

Question

Let's say we find a star that is located on the points or circles in the sky listed in the answer choices below.  Then, on the same night, we move to a location on Earth that is some significant distance from our first location.  There will now be a different star at or on:

all of these

the celestial equator

the zenith 

the celestial north pole

the celestial south pole

Answer 1

Lets think about what each of these locations is.

the celestial sphere is the name given to the sky because it appears as if the stars are painted on a giant black sphere around the earth. So the celestial equator is the projection of the equator of the Earth on this hypothetical sphere and the north and south celestial poles define the rotation axis of the celestial sphere. We identify the locations of objects in space by their locations on the celestial sphere with respect to the celestial equator, poles and an defined line analogous to the prime meridian, just as we define locations on the earth by their positions with respect to the poles, equator, and prime meridian.

The zenith, on the other hand, is the point that is directly above the observer. The object at this point changes with position and with time.

To try to visualize this, pick a corner of the room and call it the north celestial pole and the corner diagonally opposite call it the south celestial pole, and the arc between them is the celestial equator. Now imagine that there is an object located at each of the points and somewhere on the arc. These objects are "fixed" in these locations. Look directly above yourself - assume there is an object in that position. This object is at your zenith. Now move to another location in the room. Look at the "celestial poles" and "equator" - are the objects still there? (answer should be yes) Now look to your zenith (the point/object directly above you at this new position) is it the same point/object as in the previous location? (answer should be no)

So in summary: Stars whose position is defined on the celestial sphere do not change position (on the celestial sphere - they may be seen at different locations in the sky, but will always be in the same position wrt other stars.). Stars at the zenith can and do change because the zenith is defined with respect to the observer.