1. Observing and the Sky Astronomy 311 Professor Lee Carkner Lecture 3

2. Our Point of View  We are all standing on different parts of a large spinning ball moving through space   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  Sky makes one complete rotation per 24 hours (Diurnal motion)   Sky also makes one complete rotation per year (Annual motion) 

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. The Solar Year

9. The Seasons  Tilt of Earth’s axis causes seasons   Sunlight is more direct in the summer 

10. Direct and Indirect Sunlight

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

12. Times of year  Vernal Equinox -- March  First day of spring   Summer Solstice -- June  First day of summer   Autumnal Equinox - -September  First day of autumn   Winter Solstice - December  First day of winter 

13. Changing Day Length

14. 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

15. Navigation  Latitude (degrees North of the Equator)   Only works in Northern hemisphere  Longitude (degrees East or West of the Prime Meridian running through Greenwich England) 

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

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

18. The Ecliptic  Most of the objects in the solar system have their orbits in the same plane, called the ecliptic   The ecliptic passes through 12 constellations known as the zodiac

19. Constellations of the Zodiac

20. 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

21. Astrology  The belief that the positions of heavenly bodies at the time of your birth foretells your future  Your sign is where the Sun was on the zodiac when you were born   For example: Sept 13th = Virgo, but Sun is in Leo. All star signs are about 1 month off

22. Science and Pseudoscience  Astronomy is a science, it tries to form a picture of the universe based on observation and reason. It is subject to proof 

23. Next Time  Meet back in Science 102  Read Chapter 1.6