Ch. 2 The Sky

3. is one-sixtieth of an arcminute
5. the point on the celestial sphere vertically below a given position or observer
8. of a point in an orbit past the point of periapsis measured in degrees
11. the point on the celestial sphere, due north of the observer, at which the celestial meridian intersects the celestial meridian intersects the celestial horizon
12. the imaginary point on the celestial sphere at which the meridian intersects the horizon; it is due south of the observer
13. the imaginary spherical shell formed by the sky, usually represented as an infinite sphere, the center of which is a given observer's position
14. the point on the celestial sphere that is due west of the observer, at this point the celestial equator crosses the horizon
15. a group of stars
17. is a point in the sky about which all the stars seen from the Northern Hemisphere rotate
18. can be material, visual, mathematical, or computational and are often used in the construction of scientific theories

1. any of the various groups of stars to which definite names have been given
2. alternate expression to refer to the ascendant, the point where the eastern horizon intersects the ecliptic
4. is a unit of angular measurement equal to one-sixtieth of one degree
6. a scale that measures how bright a star appears
7. the line or circle that forms the apparent boundary between earth and sky
9. is a number that is a measure of a star's brightness as seen by an observer on Earth
10. is the point in the sky about which all the stars seen from the Southern Hemisphere rotate
16. the point on the celestial sphere vertically above a given position or observer