Phases and Eclipses

1. Phases and Eclipses

2. Waxing Lunar Phases Waning 29.5 days

4. Where will the sun be when the first quarter moon is rising? The sun will be setting The sun will be due south It will be midnight The sun will also be rising

5. Synodic Period: Time to complete one cycle of phases = 29.5 days. Sidereal Period: Time to complete one orbit around the Earth = 27.3 days.

6. Lunar Eclipse

7. The Moon must be Full for a Lunar eclipse to take place.

8. Demonstration of Umbra/Penumbra

11. What type of eclipse did the previous slide illustrate? A total lunar eclipse A partial lunar eclipse A partial solar eclipse A penumbral eclipse

12. Why does the Moon look reddish during a total Lunar eclipse? Because of light scattered onto the face of the Moon that has passed through the Earth’s atmosphere.

14. Solar Eclipse

15. A Solar Eclipse will occur only if the Moon is New.

17. From any given location, how long will a typical total solar eclipse last? The entire day Hours Minutes, at most a fraction of a second

19. An Annular Eclipse will occur if the tip of the umbra of the Moon’s shadow does not quite reach the surface of the Earth:

20. The Frequency of Eclipses Solar eclipses take place only when the Moon is New, and Lunar eclipses take place only when the Moon is Full. So, does this mean that we will have both a Solar and a Lunar eclipse every month?? No! On the average, we have only two Solar eclipses and two Lunar eclipses per year. Why?? Because the Moon’s orbit is inclined to the orbit of the Earth by about 5o.

21. Solar Eclipses Lunar Eclipses • 2003 May 16 - total lunar eclipse • 2003 November 8-9 - total lunar eclipse • 2004 May 4 - total lunar eclipse • 2004 October 28 - total lunar eclipse • 2005 April 24 - penumbral lunar eclipse • 2005 October 17 - partial lunar eclipse • 2006 March 14-15 - penumbral eclipse • 2006 September 7 - partial lunar eclipse • 2007 March 3-4 - total lunar eclipse • 2007 August 28 - total lunar eclipse • 2008 February 21 - total lunar eclipse • 2008 August 16 - partial lunar eclipse • 2009 February 9 – penumbral eclipse • 2009 July 7 – penumbral eclipse • 2009 August 6 – penumbral eclipse • 2009 December 31 – partial lunar eclipse • 2003 May 31 - annular solar eclipse • 2003 November 23-24 - total solar eclipse • 2004 April 19 - partial solar eclipse • 2004 October 14 - partial solar eclipse • 2005 April 8 - annular-total solar eclipse • 2005 October 3 - annular solar eclipse • 2006 March 29 - total solar eclipse • 2006 September 22 - annular solar eclipse • 2007 March 19 - partial solar eclipse • 2007 September 11 - partial solar eclipse • 2008 February 7 - annular solar eclipse • 2008 August 1 - total solar eclipse • 2009 January 26 – annular solar eclipse • 2009 July 22 – total solar eclipse • 2010 January 15 – annular solar eclipse • 2010 July 11 – total solar eclipse

24. For a Solar eclipse to occur, not only must the Moon be New, but the Line of Nodes must point at the Sun. For a Lunar eclipse to occur, not only must the Moon be Full, but the Line of Nodes must point at the Sun. This occurs only roughly every six months.

25. What is the Line of Nodes? A line drawn from the sun to the moon The line that represents the intersection of the orbital plane of the earth and the orbital plane of the moon A line projected from the sun to the earth A line drawn from the zenith to the western point on the horizon

26. Notice we said roughly every six months. If we look at the list of recent solar and lunar eclipses, we find that the interval is actually slightly less than six months. In actual fact, the Eclipse Year is 346.62 days, about 19 days shorter than the Tropical Year.

27. This happens because the plane of the Moon’s orbit precesses with a period of about 18.6 years. This precession causes the Moon’s orbit to wobble like a hubcap.

28. The Saros Cycle After a period of 18 years, 11 1/3rd days, almost exactly the same eclipse (lunar or solar) will occur again. This period, called a Saros comes about because of a convergence of three important periods related to eclipses: • One Saros = 6585.321 days = 223 Lunar months • 19 Eclipse years = 19 X 346.62 days = 6585.78 days • 18 Tropical years = 18 X 365.25 days = 6574.5 days Thus, after one Saros Cycle, the Earth, Sun and Moon will almost exactly reproduce their relative positions, and the “same” eclipse will occur again.

29. However, because the Saros cycle is 18 yrs, 11 1/3rd days, the eclipse will occur 1/3rd of the way around the world. Thus the “same” eclipse will only occur at the same place On Earth after 3 Saros cycles, or 54 years 34 days later.

30. Example: An annular eclipse took place which was visible from the Eastern U.S. on May 30, 1984. 54 years, 34 days from then (i.e. July 3, 2038) a very similar annular eclipse will take place, also visible from the Eastern U.S.. May 30 1984 + 34 54 ========== May 64 2038 But, May has 31 days, so May 64 = June 64-31 = June 33 June has 30 days, so June 33 = July 33-30 = July 3

31. The “Great European Eclipse” of Aug 11, 1999 will once again occur in Europe on what date? Aug 22, 2017 Aug 22, 2053 Feb 11, 2000 Sept 14, 2053

32. This “super” Saros cycle was apparently known to the Greek philosopher Thales, who used it to predict the solar eclipse of 585 B.C. After the eclipse on 28 May, 585 BC Herodotus wrote: ... day was all of a sudden changed into night. This event had been foretold by Thales, the Milesian, who forewarned the Ionians of it, fixing for it the very year in which it took place. The Medes and Lydians, when they observed the change, ceased fighting, and were alike anxious to have terms of peace agreed on. However, the Saros cycle may have been known thousands of years before Thales.