Survey of the Universe Tom Burbine tburbine@mtholyoke

1. Survey of the UniverseTom Burbinetburbine@mtholyoke.edu

2. All stars rotate around Polaris throughout the evening http://www.flickr.com/photos/odalaigh/1482685365/

3. Polaris • Polaris' altitude, or height above the horizon, is equal to an observer's latitude.

4. http://www.geographyalltheway.com/ks3_geography/maps_atlases/longitude_latitude.htmhttp://www.geographyalltheway.com/ks3_geography/maps_atlases/longitude_latitude.htm

5. Celestial Coordinates • Coordinates on the celestial sphere • Right ascension – east-west position (hours, minutes, seconds) • Declination – north-south position (degrees)

6. http://www.oneminuteastronomer.com/3924/sky-coordinates/

9. Zodiac • The zodiac is an imaginary belt in the heavens extending approximately 8 degrees on either side of the Sun's apparent path (the ecliptic), that includes the apparent paths of the Moon and the planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune.

13. Question: • Why do all the planets seem to follow the same path?

14. Answer: • The planets, the Earth, and the Sun all tend to fall in the same plane called the ecliptic

15. Celestial Equator • Extension of the Earth’s equator into the Celestial Sphere

17. Question: • Why is the path of the constellations on the zodiac not on the celestial equator?

18. Answer: • The rotation axis of the Earth is inclined with respect to the ecliptic

19. Long Term Changes

20. Precession • Earth precesses like a top • Precession - phenomenon by which the axis of a spinning object (e.g. a part of a gyroscope) "wobbles" when a torque is applied to it

21. Forces • For a top, the force is gravity, which is trying to pull the top down • For the Earth, the forces are due to the pull of the Sun and Moon, which is trying to align the Earth’s axis with the ecliptic

23. Because of precession • The position of a star that corresponds to the North Celestial Pole changes

24. What causes seasons? • The tilt of the Earth’s axis relative to the ecliptic

25. Seasons

27. Solstices • Summer Solstice –June 21 – Northern Hemisphere receives its most direct sunlight • Winter Solstice – December 21 – Northern Hemisphere receives its least direct sunlight

28. Equinoxes • Sun shines equally on both hemispheres • Spring Equinox – March 21 – Northern Hemisphere goes from slightly tipped away from the Sun to slightly tipped towards • Fall Equinox – September 21 - Northern Hemisphere goes from slightly tipped toward from the Sun to slightly tipped away

29. Why does the orbital difference not matter?

30. Reasons • There is only a 3% difference in the distance from the Earth to the Sun at its farthest and closest point • The Earth is actually closer to the Sun in the winter than in the summer

31. Seasons • Everybody should watch this video on why we have seasons • http://www.learner.org/resources/series28.html?pop=yes&pid=9#

32. Any Questions?