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Putting An Observatory On The Moon's 'Dark' Side
wytcld writes: "CNN reports astronomers are pushing for a radio telescope on the 'dark side of the moon' (do real astronomers call it the 'dark side,' when it gets plenty of light?). The proposal by Yuki David Takahashi is amazing mostly because a guy just starting work on his Master's is managing major press for it. Still, a nice dream."
Remember, the money isn't spent in space -- it's spent right here on earth in order to get into space.
"Ain't no right way to do a wrong thing."
A satellite in geostationary orbit still receives a lot of radio noise from Earth. That's sort of the point of GEO, after all. On the far side of the moon, though, there's this big hunk of radio absorbing rock between the antenna and Earth, which would allow the 'scope to pick up much fainter signals.
Oh, go on, check out my job.
New Scientist has more info including a graphic of how the moon shields raido waves
http://www.kubuntu.org/
Bzzzt. But thanks for playing. The Moon rotates at exactly the same rate as it revolves. Thus it always presents the same face to the Earth. That face might be lit (full moon) or might be dark (new moon), but it is the same always. That's why the Soviet pictures (Luna 3 -- see here for one telling) were such a big deal, as they were the first time any human had seen the "dark" (better, far) side.
The Moon is "tidally locked" to the Earth. Tidal forces have adjusted its rotation so that it presents the same face, due to the equality of rotation rates and revolution rates. So something on the Far Side would indeed be shielded from Earth-based transmissions.
The Mongrel Dogs Who Teach
do real astronomers call it the 'dark side,'...
:) Really though, what is it called? I doubt it is called the 'dark side', or the 'far side', although I may be wrong.
Of course they don't. That would be foolish and un-"real astronomer"-like. They call it the 'far side'.
If this proposal does go through though, and NASA begins research and development, hopefully it will reignite interest in the moon. We shouldn't dirty up the moon, but we should definately learn more about it.
~thebabelfish
"I don't trust goats," --To Catch a Spy
The dark side of the moon does face the earth half the time. Have you ever heard of a new moon?
Bzzzt. But thanks for playing. The Moon rotates at exactly the same rate as it revolves. Thus it always presents the same face to the Earth. That face might be lit (full moon) or might be dark (new moon), but it is the same always.
Uh, I think you lose the semantic battle, even though you don't state anything factually incorrect. Sometimes the "dark side" of the moon is the facing the earth. It is just that the "dark side" of the moon isn't always the same landscape. Sometimes the Sea of Tranquillity is on the dark side, sometimes it's on the light side, but it's always on the side facing Earth.
Of course, back to the relevance of the original post, as far as radio noise goes, the side on the far side from the Earth is the dark side.
-Rob
The siderial month, the true period of the revolution of the mon around the earth is 27 days, 7 hours, 43 minutes and the period of axial rotation of the moon is 27 days, 7 hours, 43 minutes.
Thus the same side of the moon is always facing the earth.
Actually, since the moon 'woobles' a bit (libration) we can actually see about 59% of the moons surface, and 41% remains permanently hidden from view from the earth's surface.
Hence the terms 'far side' and 'dark side' of the moon.
Steve M
"Far Side" sounds like something by Gary Larson. :-)
Yes, "Far Side" is a more correct term for the side of the moon furtherest from Earth. It most certaintly isn't dark - where does the other light from the Sun when there is only a "quarter moon" in the sky? And surely the "Dark Side" would be light during a lunar eclipse. :-)
The moon's orbit around its axis is the same length as its orbit around the Earth, so the same side of the moon is always facing the Earth. When you look up there at the moon, that's the same part of the Moon you always see. That's why sticking an observatory on it means they'll always be able to point out into space, but they'll still have trouble when the sun shines on them (during a "New Moon" from our perspective) and blots out its vision of the stars with interference (which I assume would be lessen by the lack of an atmosphere to scatter waves).
L1 is between Earth and Moon, L2 is on the other side. Those positions are neutral, but unstable; however satellites can been kept in "halo" orbits around such unstable points for a long time with only relatively small fuel expenditure to keep them in the right position.
L1 and L2 are about 60,000 km above the lunar surface, if I recall correctly, so somewhat further away than geo-synchronous orbits from Earth, but they would serve a similar purpose for lunar communications. L2 is the most logical for communicating with a far side observatory; laying several thousand km of cable that has to withstand 400 degree temperature swings could get rather expensive.
Energy: time to change the picture.
May I make it clear [after several classes in astronomy] that we are in TIDAL LOCK with the moon. We always see the same side of the moon because of that. No Rotation. Thats why we call one side the dark side of the moon. Its always facing away from the earth. OF COURSE, this doesn't mean it doesn't get sunlight, it just means that it doesn't recieve any of the Solar Spectrum that we either reflect or transmit. [Radio Waves are part of the Solar Spectrum.]
So why is it good to have a Radio Telescope on the Moon? The Dark side for that matter? A clearer image of the skies, is my immediate thought. I'm sure there are far more reasons then this one, but they're all too complicated for me to speculate on.
I'm going to contribute to the rampant correction of misconceptions here. (have to do my part)
THERE IS NO PERMANENT DARK SIDE OF THE MOON
There are permanent near and far sides to the moon, as viewed from Earth. The same side of the Moon is always pointed toward the Earth. The "dark" side of the Moon is whichever side of the Moon is pointed away from the Sun at the time.
The fact that the Moon does not rotate relative to the Earth is the whole point of putting a radio observatory on the far side of the Moon. Astronomers want the Moon between their radio telescopes and the radio noise of human civilization so they can observe in peace.
Other posters have explained how one could communicate with such a facility, given that it's on the far side of the Moon, so I'm not going to go into that.
But then again, I could be wrong.
L4 and L5. Put the communications satellite in the L4 or L5 Earth-moon Lagrange point. These are the stable points. While they won't "view" the exact center of the far side disk, if the observatory is built, say, 45 degrees back from that center, a satellite can view it from L4 or L5. The observatory would still be blocked from Earth noise by a huge mass of the moon, but it would be able to see L4 or L5 (which one depending on which way it was positioned) just above the horizon all the time. And with 3 or 4 active links to it on the Earth, continuous contact could be maintained. While a satellite there would actually be in order around a virtual point, it could be a small orbit, allowing for a fixed antenna at the observatory, and potentially very high bandwidth continuous communications.
now we need to go OSS in diesel cars
Number 1 is the meteor problem, during the 2 wks in which the moon leads the earth through space, the combined gravational forces of the moon and earth significantly increase the probability of a meteor striking the telescope system if it where built on the far side
How did this get modded up to 5, Insightful?? This is totally ridiculous. a) the moon has a tiny gravitational field compared to the Earth, b) the area of the moon is tiny compared to that of the Earth - it's not going to stop an appreciable amount of meteors. The reason the Earth isn't cratered is because there aren't that many meteors anymore (compared to 3B years ago), and because water/plant life smoothes out impact craters in a relatively short period of time.
I think someone's watched Armageddon a few too many times.
The second major problem is that over half the time the telescope would be pointed at or at least exposed to the sun which in it self is a significant source of rfi.
Kind of like radio telescopes on the Earth, you mean? How could anyone do any radio astronomy on the Earth with that annoying Sun there??
I suspect we could live with this.
All opinions expressed herein are not my own; I haven't had free will since last year when aliens ate my brain.
Can anyone speculate how easy it would be to sustain a stable orbit around the moon for long periods of time?
There are 5 lagrange points in a two-body system such as earth-moon. The L2 point behind the moon is unstable, but a very small amount of station-keeping thrust every now and then would keep a relay satellite there.
The moon obscures L2 from earth. But you could do a second bounce off a satellite at L4 or L5. Those are 1/6th of the way around the orbit behind and ahead of the moon and are stable second order - a satellite drifts off the potential peak but then ends up in a stable orbit around it.
See an explanation here
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Actually, you can orbit the Moon. If you stay in a low enough orbit (less than a few 1000 km's) the
gravitational perturbation due to the Earth is small. HOWEVER, there is another source of gravitational
perturbation that will cause orbits to change in a few months: large concetrations of dense rock called
"mascons" (for "mass concentrations") formed from early lava flows. These have a large enough effect that
e.g. satellites left in lunar orbit during the Apollo program decayed and impacted the Moon within a year, as
I recall.
Human genome = 3 billion base pairs = 6 GBit. Windows + Office = 20 Gbit. Which is more impressive?
They are stable, but wide. The stability is not that stuff falls inward, but that objects would orbit around the point. But, yes, there is a risk that crap can accumulate there. But astronomers have looked and found nothing more than some dust in the Earth-Moon L4/5 points. The Sun-Jupiter and Sun-Saturn L4/5 points do have some big rocks in there.
now we need to go OSS in diesel cars