Patterns in Celestial Motion

1. Patterns in Celestial Motion By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/

2. Time counting repeating patternsin the sky • A second, 1/60 of a minute, 1/(24*60*60)=1/86,400 of a day • A minute, 1/60 of a hour, 1/(24*60)=1/1440 of a day • A hour, 1/24 of a day • DAY, originally from sun rise to sun rise or sun down to sun down, now a rotation of the earth about its axis • A week, Jewish bundling of days, sacred calendars • MONTH: originally a lunation (same moon to identical moon) • YEAR: originally a revolution of the sun around the earth through the ecliptic, now a repeat of the earth around sun in its orbit. • A decade, century, millennium: different bundling of years • PRECESSION CYCLE: originally motion of the first day of a season around the ecliptic, now cycle of the rotation axis (day and night axis) about the year axis (this angle is around 23 ½ degrees now and takes around 26,000 years) • GALACTIC YEAR: revolution of solar system about the Galactic center in an orbit of around 250 million years.

3. Day and Night most basic, what you see every day, without going into outer space!

4. From outer space since ~300BCE

5. First of all earth is round • It looks flat locally to me and you. • Aristotle, shadow of the earth on the moon during a lunar eclipse is always round. • Greek sailors observed that when ships left the harbor the top of the mast disappeared last and the bottom of the ship first. So the earth is definitely curved. • But does the central fire, the sun, move around the earth or the earth rotate.

6. History and Social Studies is very important in Science (Aerospace) • Evolution of models to explain things over time. • You really can’t understand day and night motion without folding in yearly motion particularly when you start observing the changes in the night sky through out the year. This started a long time ago. • Language, reading and writing are essential. • Mathematics, the self consistent abstraction of reality is very useful.

7. Celestial Sphere

8. Celestial sphere on Latitude Protractor

9. Celestial Sphere Rectified forthe North Pole

10. Celestial Sphere Rectified forthe Equator

11. Celestial Sphere Rectified forthe some place like here

12. 0 The Celestial Sphere • Zenith = Point on the celestial sphere directly overhead • Nadir = Point on the c.s. directly underneath (not visible!) • Celestial equator = projection of Earth’s equator onto the c.s. • North celestial pole = projection of Earth’s north pole onto the c.s.

13. 0 The Celestial Sphere (II) • From geographic latitude ℓ (northern hemisphere), you see the celestial north pole ℓ degrees above thehorizon; • From geographic latitude - ℓ (southern hemisphere),you see the celestial south pole ℓ degrees above thehorizon. 90o - ℓ ℓ • Celestial equator culminates 90o – ℓ above the horizon.

14. Night Time Star Motion

15. Round Earth Rotating now

16. Putting DAY and YEARtogether the modern way

17. 0 The Annual Motion of the sun Due to Earth’s revolution around the sun, the sun appears to move through the zodiacal constellations. The sun’s apparent path on the sky is called the ecliptic. Equivalent: The ecliptic is the projection of Earth’s orbit onto the celestial sphere.

18. 0 The Seasons (IV) Earth’s orbit (eccentricity greatly exaggerated) Earth in January Earth in July sun Earth’s distance from the sun has only a very minor influence on seasonal temperature variations.

19. 0 The Motion of the Planets (I) The planets are orbiting the sun almost exactly in the plane of the ecliptic. Jupiter Venus Mars Earth Mercury The moon is orbiting Earth in almost the same plane (ecliptic). Saturn

20. Precession