1. Phases of the Moon and Eclipses

2. O swear not by the moon, the inconstant moon, that monthly changes in her circled orb, lest that thy love prove likewise variable -- Romeo and Juliet, Act 2 scene 2

3. Objectives of Moon Phases Lesson Understand the relationship between the Moon, Earth, and Sun, that causes the Moon's phases. Understand when the different Moon phases are visible. Link the observed phases with the Moon's rise and set times.

4. What Causes the Moon’s Phases? Exactly half of the Moon is illuminated at all times=the half faces the Sun The phases result from our viewing angle of the lit side, which depends on the Moon's position in its orbit around the Earth, relative to the Sun It takes 29.5 days for the Moon to go through a full cycle of its phases.

5. Phases of the Moon On the left, you see the phases of the moon Remember, half the moon is always lit and half the moon is always dark, but we might only see a portion of the lit side

6. Waxing: moon moves from new to full (see an increasing portion of the lit side of the moon Waning: moon moves from full to new (see a decreasing portion of the lit side of the moon First Quarter: waxing moon, can see ¼ of moon Third Quarter: waning moon, can see ¼ of moon Cresent: in between the new and quarter phases Gibbous: between the quarter and full

7. Phases and Rise and Set Times The Moon's rise and set times are linked to the phases. new moon is aligned toward the Sun, so it will rise and set with the Sun full moon is opposite the sun, so it will rise at sunset, and set at sunrise. – This allows basically continuous light on the Earth during this phase; for example, the "Harvest Moon" provides light to continue harvesting the crops near the autumnal equinox. first quarter phase, the moon rises at noon, is highest at sunset, and sets at midnight.

8. The Phases of the Moon New Moon  First Quarter  Full Moon Evening Sky

9. The Phases of the Moon Full Moon  Third Quarter  New Moon Morning Sky

10. Synodic Period (lunar month) vs. Sidereal Period The moon’s synodic period is 29.53 days and sidereal period is 27.32 days. Sidereal Period: The amount of time it takes the moon to orbit the earth and appear at the same place on the celestial sphere (relative to Earth) Synodic Period:the amount of time between successive new moons, or full moons, or any two successive, similar phases (relative to the sun) Phases of the moon, however, depend on the relative positions of the Earth, moon, and Sun. Since the Earth is orbiting the Sun, these alignments occur at different absolute places in the moon's orbit each month.

11. Sidereal Period The Moon orbits Earth in a sidereal period of 27.32 days. 27.32 days EarthMoon Fixed direction in space

12. Synodic Period The Moon’s synodic period (to reach the same position relative to the sun, i.e., the same lunar phase) is 29.53 days (~ 1 month). Fixed direction in space Earth Moon Earth orbits around Sun => Direction toward Sun changes! 29.53 days

13. Eclipses In your notes, contrast solar and lunar eclipses.

16. Solar Eclipses can only occur at New Moon when the Moon passes between Earth and Sun If the Moon's shadow happens to fall upon Earth's surface at that time, we see some portion of the Sun's disk covered or 'eclipsed' by the Moon Since New Moon occurs every 29 1/2 days, you might think that we should have a solar eclipse about once a month – this doesn't happen because the Moon's orbit around Earth is tilted 5 degrees to Earth's orbit around the Sun. As a result, the Moon's shadow usually misses Earth as it passes above or below our planet at New Moon. At least twice a year, the geometry lines up just right so that some part of the Moon's shadow falls on Earth's surface and an eclipse of the Sun is seen from that region. The Moon's shadow actually has two parts: 1. Penumbra The Moon's faint outer shadow. Partial solar eclipses are visible from within the penumbral shadow. 2. Umbra The Moon's dark inner shadow. Total solar eclipses are visible from within the umbral shadow. When the Moon's penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region. Partial eclipses are dangerous to look at because the un- eclipsed part of the Sun is still very bright. You must use special filters or a home- made pinhole projector to safely watch a partial eclipse of the Sun

17. Solar Eclipses The sun appears approx. as large in the sky (same angular diameter ~ 0.5 0 ) as the moon.  When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.

18. Lunar Eclipses Occur when Earth’s shadow falls on the moon, about every 6 months (due to 5 degree tilt) Total eclipse: entire moon enters Earth’s umbra (dark part of shadow) Partial eclipse: only part of the moon enters Earth’s umbra Totality: moon is within umbra, usually 1 hour

19. Lunar Eclipses partial shadow is the Penumbra, and a zone of full shadow is the Umbra If the entire surface of the moon enters the Umbra, the lunar eclipse is total.

20. Conditions for Eclipses A solar eclipse can only occur if the moon passes a node near new moon. The moon’s orbit is inclined against the ecliptic by ~ 5 0. A lunar eclipse can only occur if the moon passes a node near full moon.