The Sun and the Moon

1. Science for Teachers The Sun and the Moon

2. The Sun: closest star • Average Star • Hydrogen—94% • Helium—5.9% • Other elements—0.1% • Distance to Earth • 8.3 light minutes • About 150 million km

3. Structure of the Sun • Photosphere—visible surface; radiates most of the light we see • Chromosphere—atmosphere just above the photosphere • Corona—outermost portion of the solar atmosphere

5. Sunspots • Dark blemishes on the sun that are cooler than the surrounding photosphere • Extremely high magnetic field • Discovered by Galileo in 1610 • 11 year cycle • Umbra—dark center • Penumbra—lighter region around the umbra

7. Prominence • Bright arching structure that extends above the solar surface

9. STELLAR SPECTRA 1. Spectral types—(apparent surface temperature) • O stars—30 000K—60 000K • B stars—10 000K—30 000K Rigel (blue star in Orion) & Spica (blue star in Virgo) • A stars—7500K—10 000K (O,B,A are all bluish white) Sirius & Vega in Lyra • F stars—6000K—7500K Polaris

10. G stars—5000K—6000K Sun & Alpha Centauri (yellowish) • K stars—3500K—5000K Arcturus & Aldebaran in Taurus • M stars—cooler yet—less than 3500K Betelgeuse (reddish)

12. The moon • The Moon rotates on its axis with a period equal to its orbital revolution period around the Earth, so that the same side always faces the Earth. • This is called a Synchronous rotation • Sidereal period—this is the period the moon takes to make one revolution around the Earth—27 1/3 days

13. 386 000 km—average distance from the Earth to the Moon. • Moon’s orbit is inclined 5° to Earth’s orbit • Sun & moon appear about the same size in our sky • Sun is 400x the moon’s diameter—but it is 400x farther away. • The Moon rises in the East & sets in the West—this is caused by the Earth’s west to east rotation

14. The Moon revolves 1/27 of the way around the Earth every 24 hours. • Earth must turn 50 minutes longer on its axis in order for the Moon to be in the same spot in the sky. • Moon rises 50 minutes later—sets 50 minutes later each day. • Since it rises 50 minutes later each day it can be seen night or day. • Opposition to the sun—seen mostly at night • Between Earth & Sun—seen mostly during the day

15. Months • 1. Early Roman calendar was based on the motions of the moon. (today a month=28, 29, 30, 31 days) • 2. Lunar month is the time from one new moon to the next—29 ½ days.

16. Why is the Moon’s revolution period = to 27 1/3 days & the lunar month = to 29 ½ days? • Earth moves around the sun 1 a day  to get back to the new moon position the moon has to revolve more than 2 extra days.

17. Eclipses • Solar eclipse—occurs when the new moon casts a dark shadow on the Earth

18. Eclipses • Lunar eclipse—occurs when the moon moves into the Earth’s shadow

19. Moon Phases Result from the motion of the moon and the percentage of the bright side that is visible on Earth Depends on the location of the moon with respect to the Sun and Earth

20. Earth’s Seasons • Earth’s seasons are caused by the tilt of Earth • (23.5º from perpendicular)

21. Tides—daily changes in elevation of ocean surface • Caused by the gravitational attraction exerted on the Earth by the moon • High • Low • Spring—higher high and lower low tides caused by alignment of the sun and moon • Neap—lower tidal range caused by the moon and sun acting on Earth at right angles