Quake3World

scared? wrote:cool...i thought that rock was completely fixed to the earth...

xer0s wrote:The moon is slowly moving away from us. Something like a few centimeters per year, isn't it?

Tidal Braking of the Earth
The Earth rotates faster than the Moon orbits the Earth (24 hours compared to 27 days).

There is therefore friction between the ocean and the seabed as the Earth turns out from underneath the ocean tidal bulges.

* This drags the ocean bulge in the eastward direction of the Earth's rotation.
* Result is that ocean tides lead the Moon by about 10-degrees

Tidal Braking in the Earth and Moon
[Click on the image to view full size (18k GIF)]

The friction from the ocean tides robs the Earth of rotational energy, acting like brake pads.

This effect is known as Tidal Braking

* Slows the Earth's rotation a tiny amount.
* The Day is getting gradually longer by 0.0023 seconds per century.

Lunar Recession
Another effect of the Tidal Braking is that the extra mass in the ocean bulges leading the Moon causes a small net forward tug.

* Results in a net forward acceleration of the Moon
* Moves the Moon into a slightly larger orbit

This effect is known as Lunar Recession

* Steady increase in the average Earth-Moon distance by about 3.8 cm per year.

The Lunar Recession rate is measurable using Laser Ranging experiments that use retroreflector arrays left on the Moon by the Apollo missions (Apollo 11, 14, and 15), and two Soviet landers (Lunakhod 1 and 2). Telescopes on Earth bounce laser beams off the reflector arrays and measure the distance to the Moon to millimeter precision.

scared? wrote:cool...i thought that rock was completely fixed to the earth...sometimes i can even be a moron...

Fender wrote:About 3.8 cm per year.

http://www.astronomy.ohio-state.edu/~po ... tides.html

Tidal Braking of the Earth
The Earth rotates faster than the Moon orbits the Earth (24 hours compared to 27 days).

There is therefore friction between the ocean and the seabed as the Earth turns out from underneath the ocean tidal bulges.

* This drags the ocean bulge in the eastward direction of the Earth's rotation.
* Result is that ocean tides lead the Moon by about 10-degrees

Tidal Braking in the Earth and Moon
[Click on the image to view full size (18k GIF)]

The friction from the ocean tides robs the Earth of rotational energy, acting like brake pads.

This effect is known as Tidal Braking

* Slows the Earth's rotation a tiny amount.
* The Day is getting gradually longer by 0.0023 seconds per century.

Lunar Recession
Another effect of the Tidal Braking is that the extra mass in the ocean bulges leading the Moon causes a small net forward tug.

* Results in a net forward acceleration of the Moon
* Moves the Moon into a slightly larger orbit

This effect is known as Lunar Recession

* Steady increase in the average Earth-Moon distance by about 3.8 cm per year.

The Lunar Recession rate is measurable using Laser Ranging experiments that use retroreflector arrays left on the Moon by the Apollo missions (Apollo 11, 14, and 15), and two Soviet landers (Lunakhod 1 and 2). Telescopes on Earth bounce laser beams off the reflector arrays and measure the distance to the Moon to millimeter precision.

I knew that the moon was getting further away, but didn't know why. Kinda cool.

Didn't they teach us in school that the same side of the Moon always faces Earth? Yes, but that's only approximately true. Because the Moon's orbit is slightly elliptical (5%) and slightly tilted (5o), we view each month's full Moon from a slightly different distance and angle. The rocking motions are called libration; because of them we can observe not just 50% but rather 59% of the Moon's surface.