1. Observing Astronomy 315 Professor Lee Carkner Lecture 3

2. Our Point of View • Think about the motions of the heavens from different points of view • Remember that everything is moving at once

3. The Changing Sky • North Pole of the Earth is pointed at Polaris (the North or Pole star), which stays stationary as the other stars move around it • Caused by the rotation of the Earth on its axis • Caused by the motion of the Earth around the Sun

4. Diurnal Motion

5. Annual Motion

6. The Observer’s View

7. Observing • Can measure distance on the sky in degrees (360 degrees = complete circle) • Horizon -- • Zenith -- • Meridian --

8. Time and the Stars • Stars make one complete circuit around the sky in 24 hours • Example: if stars move 1/12 of the way around the sky, 2 hours have passed • Big Dipper is circumpolar (never sets)

9. The Solar Year

10. The Seasons • When the northern hemisphere is pointed at the Sun, it is summer here • Seasons are not caused by Earth being more or less distant from the Sun!!!

11. Direct and Indirect Sunlight

12. Solstice and Equinox • Solstice • When the Sun is highest or lowest in the sky • Equinox • When the Sun is overhead at the equator

13. Vernal Equinox -- March First day of spring Summer Solstice -- June First day of summer Autumnal Equinox --September Day and night equal in length Winter Solstice -December Shortest day of the year Times of year

14. Changing Day Length

15. Lines on a Globe • Equator -- Sun is overhead at equinox • Tropic of Capricorn -- • Tropic of Cancer -- • Arctic and Antarctic Circles -- 23 1/2 degrees south or north of the pole, Sun never sets or rises at solstice time

16. Navigation • Latitude (degrees North of the Equator) • Longitude (degrees East or West of the Prime Meridian running through Greenwich England)

17. The Celestial Sphere • Project the lines on a globe into space to form a coordinate system • North Celestial Pole -- • Celestial Equator --

18. Celestial Coordinates • Right Ascension -- • Declination -- • The coordinates do not move or vary with location on the Earth, they are fixed to the stars

19. The Ecliptic • For observers the ecliptic is a line on the sky where the Sun, Moon and planets can be found

20. Constellations of the Zodiac

21. Precession • The Earth “wobbles” as it spins, causing the Earth’s axis to point at different parts of the sky • This changes where the equinoxes are in the sky

22. Astrology • The belief that the positions of heavenly bodies at the time of your birth foretells your future • For example: March 8th = Pisces, but Sun is in Aquarius. All star signs are about 1 month off

23. Science and Pseudoscience • Astrology is a pseudoscience, it uses some of the terminology of science, but its basic tenets are not subject to proof

24. Next Time • Meet back in Science 102 • Read Chapter 3.1-3.4