Transcript Phases of the Moon

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
Phase
New
Waxing Crescent
First Quarter
Waxing Crescent
Full
Waning Gibbous
Third Quarter
Waning Crescent
Rising
6 am
9 am
Noon
3 pm
6 pm
9 pm
Midnight
3 am
Meridian
Noon
3 pm
6 pm
9 pm
Midnight
3 am
6 am
9 am
Setting
6 pm
9 pm
Midnight
3 am
6 am
9 am
Noon
3 pm
*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.