the cycles of the moon. moon basics…? what is the period of the moon? what are the phases of the...
TRANSCRIPT
The Cycles of the Moon
Moon Basics…?
• What is the period of the Moon?• What are the phases of the Moon?• When can you see the different
phases of the Moon?• Does the Moon rotate as is revolves?• Does the Moon cause our tides?• What are tides?• What are eclipses?• Can we predict them?
Sidereal Period (1)The Sidereal period is the time it takes the moon to go around Earth WITH RESPECT TO THE STARS.
Start with the moon lined up with some background stars. Now have the moon revolve around Earth.
Sidereal Period (2)
Sidereal Period27.32 days
From our position on Earth, the moon goes around and then is again lined up with the stars behind it.
Sidereal Period (3)
Sidereal Period27.32 days
Note, however, that the moon no longer lines up with the Sun. It would need to go a bit further for that.
Synodic Period
Sidereal27.32 days
Synodic 29.53 days
The Synodic period is the time it takes the moon to go around Earth WITH RESPECT TO THE SUN.
The moon must go a bit further to line up with the Sun again.
Sunlight
Sunlight
Sunlight
Crescent
Crescent
Gibbous
Gibbous
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing
Waxing
Waning Waning
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Which phase is overhead at…?
What time is the phase overhead…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
What time does the 1st Quarter moon rise? Set?
Point the arrow at the phase and it will tell you the rise and set time.
The 1st Quarter rises at noon and sets at midnight.
RiseSet
PH
AS
E
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
What time does the Waxing Gibbous moon rise? Set?
Point the arrow at the phase and it will tell you the rise and set time.
The Waxing Gibbous rises at 3 pm and sets at 3 am.
Rise
Set
PHASE
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
What time does the Waning Crescent moon rise? Set?
Point the arrow at the phase and it will tell you the rise and set time.
The Waning Crescent rises at 3 am and sets at 3 pm.
Rise
Set
PHASE
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Which phase rises at…?
Which phase sets at…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
The “phase” rises at…?
The “phase” sets at…?
Which phase is overhead at 11 pm?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Which phase is overhead at 11 pm?
There are 4 points to the orbit
and 4 areas.
Waxing Gibbous
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Which phase rises/sets at…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
W
E
Which way would you look to see…?
Ris
eS
et
PHASE
If you went out at 6 pm on the night of the full moon, which way would you look to see it?
Eas
tW
est
You would look to the East.
The Full Moon would be rising on your eastern horizon.
Using the paper method
6 pm is on the East side.
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Which way would you look to see…?
If you went out at 6 pm on the night of the waxing crescent, which way would you look to see it?
Rise
Set
PHASE
East
West
Using the paper method
6 pm is on the West side.
You would look to the West.
The waxing crescent would be setting in the west.
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Clockwise = West
Counterclockwise = East
Which way would you look to see…?
If you went out at 6 pm on the night of the full moon, which way would you look to see it?
In your head method
Start at the time
Rotate toward the phase
You would look in a counterclockwise direction… East.
The Full Moon would be rising on your eastern horizon.
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
Clockwise = West
Counterclockwise = East
Which way would you look to see…?
If you went out at 6 am on the night of the waning gibbous, which way would you look to see it?
Start at the time
Rotate toward the phase
You would look in a clockwise direction… West.
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
W
E
Clockwise = West
Counterclockwise = East
Which way would you look to see…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
W
E
Clockwise = West
Counterclockwise = East
If you went out at 6 pm every night for a month, which phases would you see?
New Moon (but you can’t see it), waxing crescent, 1st Quarter, Waxing Gibbous, Full Moon.
There are always 5 possibilities!
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
W
E
Clockwise = West
Counterclockwise = East
If you went out at 1 am every night for a month, which phases would you see?
Waxing Gibbous, Full Moon, Waning Gibbous, 3rd Quarter, Waning Crescent
There are always 5 possibilities!
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
NoonMidnight
3 pm6 pm
9 pm
9 am6 am
3 am
W
E
Clockwise = West
Counterclockwise = East
What phases would you see during the month at…?
Other websites
A good tool to test yourself on moon phases can be found at:http://www.calvin.edu/~lmolnar/moon/Tool.htmlThis tool requires JAVA.This website also has a good moon tutorial.
This is a great animation of moon phases!http://astro.unl.edu/naap/lps/animations/lps.swf
The Tides
Tides are due to gravitational force on Earth from Moon – force on near side of Earth is greater than force on far side. Water can flow freely in response.
Spring and Neap TidesThe Sun is also producing tidal effects, about half as strong as the Moon.
• Near Full and New Moon, those two effects add up to cause spring tides.
• Near first and third quarter, the two effects work at a right angle, causing neap tides.
Spring tides
Neap tides
The Tides
Tides tend to exert a “drag” force on the Earth, slowing its rotation.
This will continue until the Earth rotates synchronously with the Moon, so that the same side of the Earth always points toward the Moon.
Acceleration of the Moon’s Orbital Motion
Earth’s tidal bulges are slightly tilted in the direction of Earth’s rotation.
Gravitational force pulls the moon slightly forward along its orbit. This causes the Moon to recede at 2” per year. (3.8 cm)
The Tidally-Locked Orbit of the Moon
The Earth also exerts tidal forces on the moon’s rocky interior.
It is rotating with the same period around its axis as it is orbiting Earth (tidally locked).
We always see the same side of the moon facing Earth.
The Tidal Effects
Bay of Fundy – The difference between high and low tide can be 48 feet – 5 stories tall!
Pluto and Charon – tidally locked.
Io – resonant orbital interactions between Io and Europa, Ganymede, and Jupiter cause 100 m tidal bulges that move, stretch and bend the moon.
Eclipses
Eclipses occur when Earth, Moon, and Sun form a straight line
Motion of the Moon
Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane.
Conditions for Eclipses (1)
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 ~ 50.
A lunar eclipse can only occur if the moon passes a node near full moon.
Lunar EclipsesEarth’s shadow consists of a zone of partial shadow, the Penumbra, and a zone of full shadow, the Umbra.
If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse.
If the entire surface of the moon enters the Umbra, the lunar eclipse is total.
A Total Lunar Eclipse
Aug 2007 Eclipse
A Total Lunar EclipseA total lunar eclipse can last up to 1 hour and 40 min.
During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in Earth’s atmosphere.
Lunar Eclipses: 2008-2014
Typically, 1 or 2 lunar
eclipses per year.
Solar Eclipses
The sun appears approx. as large in the sky (same angular diameter ~ 0.50) as the moon.
When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.
Solar Eclipse – China 2009
Diamond Ring Effect
Solar Atmosphere Revealed
Solar Eclipses: 2008-2017Approximately 1 total solar eclipse per year
Earth and Moon’s Orbits Are Slightly Elliptical
Sun
Earth
Moon
(Eccentricities greatly exaggerated!)
Perihelion = position closest to the sun
Aphelion = position furthest away
from the sun
Perigee = position closest to Earth
Apogee = position furthest away from Earth
Annular Solar EclipsesThe angular sizes of the moon and the sun vary, depending on their distance from Earth.
When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse.Perigee Apogee Perihelion Aphelion
Annular Solar Eclipses (2)
Almost total, annular eclipse of May 30, 1984
The Saros Cycle
The cycle is 6585.3213 days.~ 18 years 11 1/3 days.
