Caption: The celestial sphere, the horizon for a latitude north of the tropics, and the paths of the Sun on the solstices and equinoxes.

Features:

1. The diagram is not-to-scale.

   The Earth is point compared to the celestial sphere. An observer on the Earth is a point compared to the quasi-infinite plane defined by the horizon.

2. The horizon is a great circle that cuts the celestial sphere in half.

3. The observer ideally sees everything above the horizon and nothing below.

4. In the Earth-at-rest perspective, the celestial sphere rotates westward one per sidereal day.

5. The sidereal day = 23:56:4.0905 = 86164.0905 s = 1 day - 4 m + 4.0905 s (on average) is the rotation period relative to the observable universe: i.e., to the bulk mass-energy of observable universe)---it is the true physical-motivated rotation period of the Earth.

   The sidereal day is ∼ 4 minutes shorter than the solar day.

   The solar day is defined as solar noon to solar noon and is currently about 86400.002 s.

   The standard civil day is defined as exactly 86400 s = 24 hours.

6. All natural astronomical objects are carried by the celestial sphere as their primary apparent motion.

7. The projection of the celestial axis on the horizon plane defines due north and due south.

8. The intersections of the horizon and the celestial equator define due east and due west.

   The due north-due south and due east-due west lines are perpendicular to each other.

9. During the course of a solar year, the Sun moves eastward on the ecliptic (which is NOT shown for clarity in the diagram).

10. The ecliptic is a great circle that intersects the celestial equator at two points: the vernal equinox (0 h RA) (AKA First Point of Aries) and the fall equinox.

11. The ecliptic is tilted from the celestial equator by an angle equal to the Earth's axial tilt 23.4°.

12. The summer solstice and winter solstice are, respectively, the highest and lowest points in declination of the ecliptic on the celestial sphere.

13. On the days of the solstices and equinoxes the Sun is carried around the daily rotation of the celestial sphere on the paths shown in the figure.

    Diagrammatically, it should be qualitatively clear on these days where the Sun rises and sets and how long daytime and nighttime are.

14. By mentally sliding the horizon plane north and south on the point-like Earth, you should be able to see how the behavior of the sunrise, sunset, and daytime and nighttime length vary with latitude.

15. Extreme behaviors occur at the North Pole, South Pole, Tropic of Cancer, Tropic of Capricorn, and equator. The power of your imagination should tell you what those behaviors are.