For an Earthly observer to be able to see 100% of the illuminated surface of the Moon at any given time, it should be required that the Sun be directly behind them from their position. In which case the Moon will be in the shadow of the Earth.
Is it that we are only ever able to truly view 99% of this illuminated area, but that we simply say that it is "full"?
Or is there a variable I have failed to consider?
Thanks for your time.
2006-10-07 03:27:32 · 10 answers · asked by anony m 1 in Science & Mathematics ➔ Astronomy & Space
You are right that for the moon to be 100% full, it would have to be directly opposite the sun, which only happens during a lunar eclipse.
Most of the time, the moon passes north or south of the Earth's shadow because of the inclination of the orbits. However, it is "close enough" for the moon to appear full.
The specific time of the full moon is that where its east-west position is exactly opposite that of the sun, even though it might be a few degrees north or south of the Earth's shadow.
2006-10-07 03:37:28 · answer #1 · answered by Rochester 4 · 1⤊ 0⤋
We never do see 100% of the lit surface of the moon, for the reason you posted. One of the answerers mentioned libration, and it was correct as far as it went. Another cause of libration is the non-circularity of the orbit of the moon. When it is closest to the earth it revolves faster, and when it is farther away it revolves more slowly. But, because the rotation of the moon is constant we can see a bit more of the eastern hemisphere, then a bit more of the western hemisphere of the moon. In all, we see about 59% of the surface of the moon. In addition, since we are not at an infinite distance from the moon, which is continuously curving body, we never, in any event, could see exactly 50% at a time (the apparent edges, or limbs, basically hide themselves by their own curvature). This amount we can't see is quite small, however, due to the relatively large distance between us and the moon.
2006-10-07 14:35:09 · answer #2 · answered by David A 5 · 0⤊ 0⤋
It is possible because the earth is so far from the sun the alignment would have to be just right when the sun is behind us and the moon is in front of us for the earth to block out the sun, which is why lunar eclipses only happen once in a while. 100% illumination from the moon only occurs roughly every other month.
2006-10-07 10:35:06 · answer #3 · answered by C-Dubs 2 · 0⤊ 0⤋
Hi. The others answers give you a good idea (that the Moon rises as the Sun sets and if they lined up perfectly, the Earth's shadow would cause a lunar eclipse) but did you know that the Moon wobbles a bit from our point of view? Because the orbit is tilted a few degrees, we can actually see more than half of the surface at different times. The motion is called 'libration' : http://www.phy6.org/stargaze/Smoon4.htm . So over time we have seen more than half of the Moon's surface from Earth.
2006-10-07 10:54:16 · answer #4 · answered by Cirric 7 · 1⤊ 1⤋
I suppose your observation is valid... we would only truely see 100% of the moon's lit surface if the earth was the source of light and not the sun. Its a simple matter of triangulation... however, the distances are so great and the angles so small that it is possible to say that we can see basically everything you'd see anyway on a full moon night.
2006-10-07 10:35:29 · answer #5 · answered by wreck_beach 4 · 1⤊ 0⤋
The overlapping of the Earth's shadow on the Moon is called a lunar eclipse, which only occurs one or two times a year, since the orbit of the Moon is not strictly in the same plane as Earth's orbit:
http://www.mreclipse.com/Special/LEprimer.html
http://sunearth.gsfc.nasa.gov/eclipse/lunar.html
As it turns outs, the full Moon is not quite full, biut it's awfully close, since the maximum shown below is 99.9%
http://sunearth.gsfc.nasa.gov/eclipse/TYPE/moon4.html#mo2006
2006-10-07 12:06:47 · answer #6 · answered by arbiter007 6 · 0⤊ 0⤋
No, you're correct. We never really see 100% of the illuminated part of the Moon. But it's called 'full' when we see the 'maximum' amount of its surface that we can see.
Doug
2006-10-07 11:53:43 · answer #7 · answered by doug_donaghue 7 · 2⤊ 0⤋
The time when the earth is completely out of line with the moon and the sun.
2006-10-07 10:30:57 · answer #8 · answered by Anonymous · 0⤊ 0⤋
we can see the full moon only 3 days every lunar month
2006-10-07 12:29:15 · answer #9 · answered by latif_1950 3 · 0⤊ 0⤋
The sun is a gozillion (exagerating) times bigger than earth so it shines straight past.
Like if a speck of dirt is on a light bulb, it still lights the whole floor, kindov a thing, yea!?
2006-10-07 10:33:07 · answer #10 · answered by m c 2 · 0⤊ 2⤋