Phases of the Moon New 0% Illuminated Waxing Crescent 25% Illuminated on RHS First Quarter 50% Illuminated on RHS Waxing Gibbous 75% Illuminated on RHS Full 100% Illuminated Waning Gibbous 75% Illuminated on LHS Third (Last) Quarter 50% Illuminated on LHS Waning Crescent 25% Illuminated on LHS
Rising/Meridian/Setting Times *Assuming the moon is always on the celestial equator and above the horizon 12 hours per day.
Lunar Periods • Sidereal Period – 27.3 days • The time between successive alignments of the earth, moon, and a star • The true orbital period of the moon • Synodic Period – 29.5 days • The time between successive alignments of the earth, moon, and the sun • The period of the cycle of lunar phases
Lunar Eclipses • Total Lunar Eclipse • The moon is entirely inside the earth’s umbra • Partial Lunar Eclipse • The moon is partially inside the earth’s umbra • Penumbral Lunar Eclipse • The moon is inside the Earth’s penumbra • These happen regularly and no one notices. The brightness of the moon only decreases by 10% to 20%
Solar Eclipses • Total Solar Eclipse • The moon completely obscures the sun for an observer at this location on the Earth • Partial Solar Eclipse • The moon partially obscures the sun for an observer at this location on the Earth • Annular Solar Eclipse • The moon is near apogee and its angular diameter is insufficient to completely cover the sun. An observer for whom the moon and sun are aligned will see a ring of the sun around the moon
Tides - caused by differential gravitational forces exerted by the moon (the moon pulls more on one side of the earth than the other) • Even though the sun’s gravitational force is much larger than the moon’s, its differential force is smaller (since the size of the earth is small compared to the earth-sun distance) • This moon’s differential force causes “water bulges” on the earth on both sides of the line to the moon. Tides are caused by the Earth’s rotation carrying observers through a water bulge. Thus, typically high tide occurs twice a day. • Neap Tides – weak tides which occur when the moon’s and sun’s pull are perpendicular • Spring Tides – strong tides when the moon and sun are aligned.