The Sun’s Motion in the Sky

1. The Sun’s Motion in the Sky

5. Where does sunset occur in December?

6. The Setting Sun – “The Sun doesn’t like to set”

7. Map and Unwrap the region on the Celestial sphere where the Sun travels

8. This does to the Celestial Sphere what a Mercator projection does to a globe

11. Solstices and Equinoxes mark the beginnings of their seasons

12. Get out your SFA starchartsPlace the two rectangular charts side by side Locate the Celestial Equator Locate the Ecliptic The dates written along the Ecliptic show the apparent location of the Sun throughout the year.

13. Ecliptic = The Path the Sun Travels • Zodiac = The Constellations the Sun Travels Through

14. The Solstices and Equinoxes are both: • Specific points on the celestial sphere. • Specific instants during the year when the Sun is exactly at those points.

15. Solstice = Sun Stops – compare “Armistice” • Equinox = Equal night and day (12 hours each)

16. Ecliptic (in red) on Celestial Sphere

17. What time of day is it?1.Morn, 2.Noon, 3.Eve, 4.Night

18. What is the season?1 = Sum., 2=Fall, 3=Win., 4=Spr.

19. There are 365 days in a year  Sun travels just about 1 degree per day against the celestial sphere. • In the course of 1 year, the sun makes 1 fewer revolution than the stars do.

20. 24 hours x 365/366 =23 hours and 56 minutes • 24 hours is a solar day • 23 hours 56 minutes is a sidereal day

21. TheSeasons The sun goes around the celestial sphere in 1 year. This means the seasons are connected to where the sun is on the celestial sphere.

23. Summer Solstice (June 20)(line shows daily path of Sun)

24. At the Spring and Fall Equinoxes(March 20 and September 20)

25. Winter Solstice(December 21)

27. THE MOTION OF THE SUN ALONG THE ECLIPTIC CAUSES THE SEASONS! • Two effects: • In winter, the sun is above the horizon for a smaller fraction of the day • In winter, even when it is up, the sun hits the ground at a lower angle angle.

29. Note that in winter – same amount of light is spread out over greater area

30. Practical Application in Architecture

31. The Sun’s Motion viewed from the Equator or the Pole • Tropics = Anywhere you can stand on the Earth’s surface and have the Sun directly overhead (i.e. not Wisconsin). • Arctic and Antarctic Circles = If you are anywhere closer to the pole, the Sun will not rise at least one day of the year.

33. Person Standing at the Pole:

34. Why are some years leap years?

35. Year – time for Sun to return to the same spot on the ecliptic: • Roughly 365.25 days long. • If you didn’t add a leap year, time of spring equinox would drift by 1 day every four years. In 120 years, all the months would be 1 month earlier (e.g. “May” would occur in what we call “April”)

36. Even leap year system is not perfect: Year is actually 365.242 189 67 days long • Gregorian Calendar reform: • Thursday, 4 October 1582 was followed by Friday, 15 October 1582 in many Catholic countries. • Century years (e.g. 1900) are not leap years unless they are evenly divisible by 400 (e.g. 2000)

37. “William III of England arrived at Brixham in England on 5 November (Julian calendar), after setting sail from the Netherlands on 11 November (Gregorian calendar). • Shakespeare and Cervantes apparently died on exactly the same date (23 April 1616), but in fact Cervantes predeceased Shakespeare by ten days in real time (for dating these events, Spain used the Gregorian calendar, but Britain used the Julian calendar). “1 • 1Wikipedia: Gregorian Calendar

38. Exercise 4: Planisphere -- Sun

39. Exercise 5: Hours of the Day around the World

40. Sun’s Motion through the Stars – Caused by Earth’s motion

41. Day of the year tells you exactly where the earth is on its orbit.

42. Ex 6: Earth in Orbit around the Sun Ex 7: The constellations throughout the year