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Observing. Astronomy 315 Professor Lee Carkner Lecture 3. Our Point of View. Think about the motions of the heavens from different points of view Remember that everything is moving at once. The Changing Sky.

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  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

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