The Sky

1. The Sky

2. The Sky • Constellations - Patterns of stars • There are 88 constellations in the night time sky.

3. The Sky • The Greek alphabet is used to signify the brightness of a star in a constellation • Betelgeuse (Beetle Juice) appears to be the brightest star in the constellation Orion. We would label Betelgeuse alpha Orionis, or  Orionis.

4. The Sky North celestial pole - points to Polaris, the north star. • Celestial sphere – model of the sky above us • The ecliptic is the path the sun takes in the sky. • The highest point on the ecliptic the sun reaches is the summer solstice. The lowest point is the winter solstice. Stars are on the surface of the sphere. Ecliptic Celestial equator South celestial pole

5. The Sky • The summer solstice occurs on June 21 and is, in the northern hemisphere, the day with the longest amount of daylight. • The winter solstice occurs on December 21 and is the day with the shortest amount of daylight. Summer solstice Winter solstice

6. The Sky Autumnal equinox • The equinoxes occur at the intersection points between the ecliptic and the celestial equator. Both days have equal light and darkness. • Vernal equinox occurs in the spring on March 21 • Autumnal equinox occurs in the fall on September 21 0h, 0min Vernal equinox

7. The Sky • Constellations that fall on the ecliptic are called the signs of the Zodiac. •  We recognize 12 but there are actually 13 constellations that fall on the ecliptic. •  The thirteenth constellation on the zodiac is Ophiuchus (o fee' a cus)

8. The Sky • Precession is the slow change in direction of the Earth’s rotation axis due to its spin. • The Earth is a very precise natural top. • Circumpolar constellations are those constellations that never rise or set.

9. Declination Right ascension The Sky • We can find constellations on the celestial sphere by using coordinates. We use right ascension and declination. • Right ascension is measured in hours, minutes and seconds. The Earth rotates through 360 degrees in 24 hours. • Declination is measured in degrees from the equator. • The notation is as follows: RA = 4h33m (right ascension) dec = 724' (declination)

10. Lines of Declination 90° Lines of Right ascension 45° 30° 15° 0° 22h0m 1h0m -15° 23h0m 0h0m Declination -90° The Sky

11. The Sky • Seasons occur because the Earth is tilted 23 1/2°. • The Earth is closest to the Sun in January. • The Earth is farthest from the Sun in July. • The distance to the Sun does not determine the seasons.

12. The Cycles of the Moon • Phases of the Moon • Waxing phases • Crescent • Quarter • Gibbous • Waning phases • Crescent • Quarter • Gibbous • Full moon • New moon

13. The Cycles of the Moon • Tides • 2 High tides per day • 2 Low tides per day

14. The Cycles of the Moon • Neap tide

15. The Cycles of the Moon • Spring tide

16. The Cycles of the Moon • Inner shadow is the umbra • Outer shadow is the penumbra

17. The Cycles of the Moon • Lunar eclipses • Total • Coppery in color • Partial • Partially in umbra

18. The Cycles of the Moon • Solar Eclipses • Total • Umbra • Diamond ring effect • Partial • Partially in umbra • Annular • penumbra