The Moon

1
The Moon
2
The Moon gives us
phases
tides
Solar eclipses
Lunar eclipses
3
The moons size, distance and motions
4
Phases
5
Lets start with phases
Waxing gibbous
1st quarter
Waxing crescent
6
And the rest of the phases
Full moon
Waning gibbous
Last quarter
Last crescent
7
The moons orbit around earth
9 P.M
.
3 P.M.
3 A.M.
9 A.M.
What causes these phases?
8
Because the moon rotates in exactly the same
period as It revolves, the same side of the
moon always faces earth
The moon therefore has a hidden side which is not
the same as the dark side
This hidden side was never seen by man until the
late 1960s when Apollo spacecraft first orbited
the moon
9
If the earth did not rotate, an observer could
watch the moon slowly move eastward through the
stars (0.55 degrees every hour)
So a phase is simply the portion of the lit half
of the moon that faces The earth at any point
during the moons orbit.
west
east
west
east
10
15 degrees
14.5 degrees
per hour
west
east
But because the earth rotates 15 degrees per hour
in the same direction (east) as the moon
revolves, the moon appears to move 15.0 degrees
minus 0.55 degrees, or about 14.5 degrees per
hour to the west
In other words every hour the moon loses 0.55
degrees to the background stars as they head
towards the west
11
Moons position 24 hours ago
13 degrees apart
Current moon position
East horizon
Each day the moon is 13 degrees east of where It
was
A consequence of this is the moon rises 50
minutes later each night and there is a 50 minute
delay each day in high tide
12
Because the earth also orbits the sun there is a
small difference between the time for a true
orbit of the moon once around the earth and the
time to complete the phases
True orbit period 27.3 days Month of phases
29.5 days
29.5 days
(360 deg. Orbit)
27.3 days