Celestial Sphere

1. Celestial Sphere Imagine the sky as a hollow sphere The stars are attached to this hollow sphere, they rise in the east and set in the west The Sun, Moon and the planets wander on this sphere • Celestial Sphere Very convenient But why spherical?? Pythagoras-> Shadow of the Earth

2. Celestial North pole Stars rotate around the Celestial North and the South Poles. Stars rotate parallel to the Celestial Equator. The point straight overhead is called the Zenith. The arc that goes thru the north point, zenith and the south point of the horizon is called the meridian. The position of the zenith changes when you move away from the North Pole.

3. We are looking up Your position on Earth will be defined by longitude and latitude: Latitude: distance from the Equator in degrees. Longitude: distance from the prime meridian in degrees. Stars rise in the East, pass the meridian and set in the West.

4. On the Equator North Celestial Pole disappears from sight. Stars rise and set vertically. Zenith is parallel to the celestial equator. Now we know our bearings on Earth with respect to the stars  check out the motion of the Sun and the Moon.

5. Romulus' Calendar Martius (31 days) --> Mars (War) Aprilis (30 days) --> Apru (Aphrodite) Maius (31 days) --> Maia (Fertility) Iunius (30 days) --> Juno (Marriage) Quintilis(31 days) Sextilis (30 days) September (30 days) October (31 days) November (30 days) December (30 days) --------------------------------------------- 304 days Ianuarius (29 days) --> Janus (Two faced God) Februarius (28 days) --> Februa (Purification) Martius (31 days) --> Mars (War) Aprilis (29 days) --> Apru (Aphrodite) Maius (31 days) --> Maia (Fertility) Iunius (29 days) --> Juno (Marriage) Quintilis(31 days) Sextilis (29 days) September (29 days) October (31 days) November (29 days) December (29 days) ------------------------------------------------- 355 days (almost lunar calendar) Numa Pompilius' Calendar -->

6. Julian Calendar Ianuarius (29 days) --> Ianuarius (31 days) Februarius (28 days) --> Februarius (28 days) Martius (31 days) --> Martius (31 days) Aprilis (29 days) --> Aprilis (30 days) Maius (31 days) --> Maius (31 days) Iunius (29 days) --> Iunius (30 days) Quintilis(31 days) --> Iulius (31 days) Sextilis (29 days) --> Augustus (31 days) September (29 days) --> September (30 days) October (31 days) --> October (31 days) November (29 days) --> November (30 days) December (29 days) --> December (31 days)

7. Mayan Calendar Table of Long Count units Days Long Count period Long Count unit Solar years 1 1 Kin 20 20 Kin 1 Uinal 360 18 Uinal 1 Tun ~ 1 7,200 20 Tun 1 Ka'tun 19.7 144,000 20 Ka'tun 1 Bak'tun 394.3 2,880,000 20 Bak'tun 1 Pictun 7,885 57,600,000 20 Pictun 1 Kalabtun 157,808 1,152,000,000 20 Kalabtun 1 K'inchiltun 3,156,164 23,040,000,000 20 K'inchiltun 1 Alautun 63,123,288 December 20, 2012: 12.19.19.17.19 December 21, 2012: 13.0.0.0.0

8. Sun’s path Earth moves around the Sun once every 365.24 days. Each day the Sun moves about one degree with respect to the other stars in the sky because of this motion. The yearly path of the Earth around the Sun is called the ecliptic.

9. Seasons Vernal and autumnal equinox (equal night) Winter and summer solstice (sun standing still)

10. Reasons for the Seasons Earth’s orbit is elliptical, so sometimes the Earth is closer to the Sun  But when we have summer here, it’s winter in the southern hemisphere, so this does not explain the seasons. But the tilt of the Earth does.

11. Precession of the Equinoxes Celestial North Pole points to the star Polaris at the moment. But the position of “North” changes every 26,000 years from Polaris to Vega and back. First observed by Hipparchus in 100 BC. Coming is the dawning of the Age of Aquarius (2600 A.D.)

12. Motion of the Moon Moon revolves around the Earth every 27.3 days, and rotates around itself every 27.3 days, so we always see the same face of the Moon. New moon Crescent Quarter Gibbous Full moon

13. Eclipses Moon’s orbit is tilted by 5o wrt the ecliptic. We can have a lunar/solar eclipse only when the moon cuts the ecliptic plane. But the eclipses only happen when the moon cuts the ecliptic during a full moon (lunar eclipse) or new moon (solar eclipse).

14. Solar Eclipse Because of the 5o tilt of the Moon’s orbit, Moon’s shadow misses the Earth most of the times. But once in a while (like once in every 18 months)…

15. Total Eclipse Moon’s shadow has two parts: Penumbra: Faint, outer shadow, only partial eclipse can be seen. Umbra: Dark, inner shadow with total eclipse.

16. Eclipse views

17. What’s the big deal?? "Some people see a partial eclipse and wonder why others talk so much about a total eclipse. Seeing a partial eclipse and saying that you have seen an eclipse is like standing outside an opera house and saying that you have seen the opera; in both cases, you have missed the main event."