Quote:
Originally Posted by socialjustice_fsu
Aj ~
I understand we are to experience a 'supermoon' the night of March 19, 2011.
I know this means the moon will be roughly 221,000 miles away from the earth plus it will be a full moon. I know this occurs every 18 years. Can you explain this event and it's impact, if any, upon our planet?
Signed,
The One Who Slept Through Astronomy
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Sorry that I missed answering this during my hiatus. I know the event has passed but here is the response even though it is late:
Orbits are stable but they are not perfect, which means that they are not precisely circular. Our orbit around the Sun is an elipsis and the Moon's orbit around Earth is also an elipsis. This means that there are points of the orbit where the smaller (less massive) object will be closer to the larger (more massive) object and points where it will farther away. The 'supermoon' is simply an artifact of orbits being elliptical.
Normally, the Moon orbits the Earth at ~250,000 miles. At its closest this distance closes to ~220,000 miles which is about 10% of the total distance. So what effects occur? As you know now, not a lot happened and this is what we should expect. Why? Well, even as the Earth's mass pulls on the Moon the Moon's mass pulls on the water. The reason this happens is that while most of the mass of the Earth is stationary, the waters are constantly in motion. This means that the Earth's center of gravitational mass has a slightly less firm hold on the water than on other objects. Because gravity is a field and all fields fall off in strength as an inverse of the square of the distance* from the source of that field the closer the Earth and the Moon are to one another, the more intense the tides will be on Earth.
As far as the full-moon, this has no effect because of why there are phases of the moon in the first place. The reason why there are phases is that the moon is tidally locked with the Earth. What this means is that the rotation of the moon on its access, is in synchronization with its rotation around the Earth. This means that the same face of the moon always points toward us. Since the same part of the Moon always faces Earth, when the moon is new it means that all of the solar light striking the surface of the moon is hitting the side pointed away from us and when the moon is full the solar light is hitting the part pointed toward us. To see how this works you can do a very simple experiment with you and two other people.
Have one person stand stationary at a single point in the center of the room with a flashlight--that person represents the sun. Now, you and one other person stand facing one another and move in sync in a circle around the person holding the flashlight. If you are the person in the position of the Earth you will always be looking at the face of the person opposite you. However, when the "moon" person has their face pointed toward the flashlight, you will see their face--this is a full moon when their face is pointed away from the moon you will not see their face. Obviously to get the best effect this should take place in a darkened room.
Since the only difference between a full moon and a new moon is which face is getting the light there's no effects of a full or new moon on Earth because gravitationally they have not changed in relationship to one another.
Hope this helps.
cheers
Aj
*The inverse square law is a physical law that says that as the distance from a field increases the strength of the field decreases as a function of the square of the distance. So at twice the distance the field has fallen off not two times but *four* times the distance. At four times the distance from the source the strength of the field has fallen off to sixteen times the intensity which can be found at its source. This applies to all fields in all mediums. This means that it applies to gravity, sound and electromagnetic fields. So let's say that there is a field that, just for the sake of ease, we will say has a strength of '16' at its source. Every ten feet the strength of the field will decrease. This means that at 10 feet from the source it has a strength of four, at 20 a strength of 2, at 30 a strength of 1.4, at 40 feet a strength of 1.2, at 50 feet a strength of 1.1, etc. (I've rounded up just to make it easy) The next time you are driving and you hear a siren, pay attention to how quickly the sound becomes intense as the siren comes toward you and how quickly it falls off as the sound moves away from you. This is the inverse square law in action, the very same thing happens with light or any other field. Dropping a rock into still water will also give you the same effect.