GE 150 Astronomy

1. GE 150 Astronomy Week #2 January 21,23 2014

2. Celestial Sphere Nightly Motions

3. Star B Celestial Sphere Rotation 2 Star A 1 2 Celestial Sphere 3 1 4 3 Horizon 4 Celestial Sphere Rotation Nightly Motion of the Stars Celestial Sphere

4. Celestial Sphere – Daily Motions North Pole looking down

5. Earth’s rotation causes the Sun, Planets, Moon and stars to appear to move east-to-west when viewed from Earth

6. Nightly Motion of the Stars • Imagine looking toward the East as a star rises above your horizon - what does it do after that?

7. Nightly Motion of the Stars • For stars (this can include the Moon and planets, even the Sun) that appear in the southern sky: Stars first rise near the eastern horizon, move upward and toward the south, and then move down and set near the western horizon.

9. Nightly Motion of the Stars • Imagine looking toward the North. What do stars appear to do over the course of an evening?

10. Nightly Motion of the Stars North Star • Looking North: Stars appear to move counter-clockwise around the stationary North Star (Polaris) • these are circumpolar stars. W N E

11. What happens over time in the Northern Sky?

13. Seasonal Stars Yearly Changes

17. The Zodiac The constellations that mark the path of the Sun (i.e. stars blocked by the Sun) in the sky throughout the year Ecliptic – the line through the Zodiac that Sun follows Ecliptic – the line through the Zodiac that marks the plane of the Earth’s orbit

18. Leo Libra Virgo Scorpius Ophiuchus Sagittarius Capricornus The Zodiac • Aquarius • Pisces • Aries • Taurus • Gemini • Cancer Officially, there are 13 constellations that our Sun covers-up (blocks) in the course of one year (used to be only 12) Note: Constellation name is different from the astrological symbol The ‘new’ member

19. Your Birth Sign • ROUGHLY, it is the constellation that the Sun is covering up during the day you are born. • That is if you were born 2000 years ago.

20. Zodiac Signs Then and Now

22. The Zodiacal Constellations that our Sun covers-up (blocks) in the course of one year (only 12 are shown here) North Star Taurus Aries Gemini South Pisces Cancer Figure 2 – What it would look like if you were the observer in Figure 1 Aquarius Pisces Capricornus Aries 1 day Sagittarius Taurus Scorpius 365 days Libra Gemini Virgo Cancer Leo Figure 1 Which constellation is the Sun covering for the situation shown?

23. Two months from the time shown what constellation will be high in the Southern sky, at Midnight? At Noon? North Star W E W E Taurus Aries Gemini South Pisces Cancer Figure 2 – What it would look like if you were the observer in Figure 1 What sign will a person be if they are born at that time? Aquarius Pisces Capricornus Aries 1 day Sagittarius Taurus Scorpius 365 days Libra Gemini Virgo Cancer Leo Figure 1

24. W W E E Taurus Aries Gemini South Pisces Cancer “Today” at Midnight Two months from the time shown Cancer will be high in the Southern sky. at Midnight Cancer Leo Gemini Taurus South Virgo Two months later at Midnight

25. W W E E Taurus Aries Gemini South Pisces Cancer “Today” at Midnight “Today” at Midnight: Cancer is just rising In two months at Midnight: Cancer will be high in the south, i.e. it had to rise several hours earlier Cancer Leo Gemini Conclusion: Stars rise just a bit earlier each day due to Earth moving in its orbit Taurus South Virgo Two months later at Midnight

26. Path of the Sun Yearly Changes

27. The changing position of the Sun during the year! March 20th/Sept. 22nd December 21st June 20th Zenith E S N W Sun at Noon throughout the year

28. How can we describe the motion of the sun in the sky? meridian zenith LUNCH!! PM or post meridian AM or ante meridian east south west

29. Where is the Sun throughout the year? June 21 Summer Solstice Mar 21 (Vernal) and Sept 21 (Autumnal) Equinox Dec 21 Winter Solstice zenith east south west

30. The time for the sun to go from being highest in the sky at noon, to lowest and back to highest again is… zenith east south west

31. Position of the Sun when photographed during the day of the winter and summer solstice

32. Season Stats • Vernal Equinox – March 21st • Equinox – “Equal Night” 12 hours of daylight/nighttime • Start of spring in Northern Hemisphere, Fall in Southern • Summer Solstice – June 22nd • Solstice - Sun (sol) stands still (sistere) • Longest day Northern hemisphere, shortest in the Southern • Autumnal Equinox – September 23rd • Start of fall in Northern Hemisphere, Spring in the Southern • Winter Solstice – December 22nd • Shortest day Northern hemisphere, longest in the Southern