1. Earth Motions
(Astronomy I)

2. I. Celestial Observations
A. Celestial Objects: a natural object observed in space that is not of Earth.
Ex. Sun, moon, comets, asteroids, planets, stars.

4. B. Celestial Sphere: the imaginary sphere that encircles Earth.
Zenith: point directly over the observer’s head.
*Just look straight up!

5. C. The Horizon System: used to locate points on the celestial sphere
C. The Horizon System: used to locate points on the celestial sphere. Requires the altitude and azimuth of an object.
1. Altitude: vertical distance above the horizon in degrees. (like latitude)
2. Azimuth: horizontal distance in degrees measured from due North or 0 degrees. (like longitude)

6. Sun’s Coordinates: http://mikescosmos.com/SolarAZ.php

7. D. Apparent Motion of Celestial Objects: rate of motion is 15 degrees/hr in the shape of an arc.
1. Star Trails: created when long exposure photos are taken of stars.

8. If this angle is 15 degree, how long is this time exposure?

9. II. Rotation: the spinning of an object on an imaginary axis
II. Rotation: the spinning of an object on an imaginary axis. Video: 3:20
A. Earth’s Rotation:
1. West to East (counter clockwise)
2. 1 rotation = 24 hrs.
3. Earth’s axis of rotation is tilted 23.5 degrees
4. Rotates fastest at the equator.

13. B. Evidence of Earth’s Rotation:
1. Day and night
2. Apparent movement of sun, stars and moon east to west across the southern portion of the sky in the northern hemisphere.
3. Foucault’s pendulum: the swing of the pendulum appears to change direction.

15. 4. Coriolis effect: the deflection of air and water currents.
a. To the right in the northern hemisphere.
b. To the left in the southern hemisphere.

16. III. Revolution: the orbiting of one celestial body around another.
A. Earth’s revolution:
1. Counter clockwise around the sun.
2. 1 revolution = 1 year (365 days)
3. Rate = 1 degree/day
4. Earth’s axis points in the same direction throughout its revolution (parallelism).

17. B. Evidence of Earth Revolution:
1. Diff. constellations are viewed at different times of the year.

19. 2. The Seasons: caused by the tilt of Earth’s axis and the angle of the sun’s rays. Not the distance to the sun!

20. S
Video: 0:55 Seasonal Changes; 0:50 Seasons in No. and So. Hemisphere; 1:07 Seasons on No. and So. Poles

21. Seasons and ecliptic simulator

22. a. The Summer Solstice: (6/21) first day of summer!
* Longest daylight hours of the year (15 hrs).
* Sun is highest in the sky
* North pole is tilted towards the Sun
* Sun is directly overhead at the Tropic of Cancer (23.5 N. lat.)

23. b. The Equinoxes: Fall 9/21 & 3/21(autumnal)/Spring (vernal):
* Equal number of day and night hours (12)
* Neither pole is tilted towards the sun
* Sun is directly overhead at the equator.

24. c. Winter Solstice: first day of winter (12/21)
* Shortest daylight hours of the year (9 hrs)
* Sun is lowest in the sky
* South pole is tilted towards the sun
Sun is directly overhead at the Tropic of Capricorn
(23.5 S. lat.)

25. 3. Apparent path of the sun: changes with the seasons as Earth revolves in a cyclic pattern.
* Altitude of the sun at noon varies with lat.
* The sun is never directly overhead in N.Y. !!

26. the higher the Sun’s altitude, the shorter the shadow.
a. Length of Shadows: shadow lengths change based on the altitude of the Sun.
the higher the Sun’s altitude, the shorter the shadow.
Sun’s altitude changes throughout the day
Sun rise (east), noon (due south), Sun set (west)
Sun’s altitude changes throughout the year
Winter (Sun is low in sky); Summer (Sun is high in sky)
* shadows are cast in the opposite direction of the Sun’s position in the sky.
* Notice the changing length of the shadow.

27. Morning
Afternoon
Noon

28. b. Angle of Insolation: the angle at which the sun’s rays strike Earth’s surface.
The higher the sun, the greater the angle of intensity.
2. The greater the angle of intensity, the higher the temperture.

29. C. Duration of Insolation: the number of daylight hours.
The longer the sun’s path, the greater the duration of insolation (Incoming Solar Radiation).
2. In NYS:
6/21= 15 hrs.
9/21 & 3/21= 12 hrs.
12/21= 9 hrs.