Click on the link below to view a lunar phases animation
This link actually slows down the animation.
Can you answer the questions below?
Why is the Moon apparently changing size?
What is the phase at this particular month's perigee?
During what part of the month is the Moon apparently rocking to the right? To the left?
What causes the right/left rocking?
Explain why we see more of the left (eastern) limb of the Moon sometimes, and other times more of the right limb.
Explain why we see a little more of the south polar regions at some times, and more of the north polar region at others.
What was the phase of the Moon when it was a maximum +declination this month?
ANSWERS
The Moon's elliptical orbit brings it closer (so it appears larger, to a point in its orbit called perigee) and farther (looks smaller, at apogee) from Earth in the course of a "moonth". Perigee occurs at new (waxing) crescent phase. The Moon rocks to the right between the new crescent and the old gibbous, and to the left between the old gibbous and new crescent. We see it rock because as the moon's revolution slows as it moves from perigee to apogee, we get to see a little more of the left side of it (because its rotation rate is constant). As the revolution speeds up, a little more of the right side is revealed to an earthbound observer. We see more and less of the poles becaus, the Moon's orbit is inclined with respect to equator (the moon, in a single month, covers a greater range of declination (the "latitude" of the sky) than the Sun does in a year. When the Moon is at it's greatest +declination (29 deg north of the equator), we see a little more of the south polar region as we "look up" at the Moon (and that seems to be right around the full phase in the animation). At its greatest -declination (29 deg south of the equator), two weeks later, we see more of the north polar region as we "look down" on the moon. (see the diagram below)
