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Radio Telescopes on Moon to Study Cosmic Dark Ages
The Narrative Fallacy brings news that NASA has awarded a $500,000 grant to develop plans for an array of radio telescopes to be located on the moon. The telescopes would be used to gather data from the earliest stars and galaxies, observations of which are difficult from Earth due to the ionosphere and terrestrial broadcasts. The grant was part of NASA's sponsoring of 19 "Next Generation Astronomy Missions." Quoting:
"The Lunar Array for Radio Cosmology (LARC) project ... is planned as a huge array of hundreds of telescope modules designed to pick up very-low-frequency radio emissions. The array will cover an area of up to two square kilometers; the modules would be moved into place on the lunar surface by automated vehicles. The new lunar telescopes would add greatly to the capabilities of a low-frequency radio telescope array now under construction in Western Australia, one of the most radio-quiet areas on Earth."
Just a bit far to go on a LARC, ain't it?
/british >
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In Xanadu did Kubla Khan
A stately pleasure dome decree
The moon makes for an excellent platform for automated telescopes. People are going to bring up the tired "appolo for diamonds" argument but it doesn't have any bearing on this. The moon has no atmosphere to speak of, little radio interference from the earth and ample room to set up a large array.
This requires less investment than manned missions (which dictate a return and have a HUGE space/safety cost). It will allow us to see other things than what is suggested in the grant--Changra, hubble and the like all have been used for things that were not conceived of during the design phase.
ditto
Oh wait was I supposed to say something witty here?!?
The moon goes around the Earth, one face always faces the Earth. Over the course of 28 days the dark side of the moon will see the entire sky with a giant ball of rock in between the observatory and Earth
Like most of NASA's programs, this basically amounts to a jobs program for scientists/engineers. Notice that the funding is for the plans for an array of telescopes, not for the actual construction of said array. Building an array of telescopes on the Moon would likely require astronauts to spend months on the Moon, even if most of the telescopes came pre-assembled. Without any infrastructure on the Moon to support those astronauts, building an array of telescopes there is a pipe dream, and will remain so for the foreseeable future.
If any plans end up being actually produced, they'll likely be filed away in a drawer and forgotten. Pessimistic? Sure. But, that's the way NASA has worked for decades now.
Why not just put the telescopes in a geostationary orbit around the Moon so they are always on the dark side and therefore shielded from the Earth? Soft landing telescopes of any significant size is hard work. The only reason lunar telescopes makes more sense than space telescopes in lunar orbit is if you build the lunar telescopes from lunar materials... and we're not anywhere near that capability yet.
How we know is more important than what we know.
Well, not quite.
This type of observatory requires a lot of smaller units that add up to a total resolution of the receiving surface. The best resolution is directly overhead of the site. As you try to observe items that are low on the horizon, you lose a great deal of the quality of the observation as the effective size of the array is diminished.
For example:
**** (what you are observing)
^^^^ (The array).
The array is effectively as wide as its deployment diameter.
Now, suppose you are observing from a couple other angles:
****
^^^^
From that angle, the array is apparently smaller. You can angle them to make sure you have the same strength, but you have to increase the size of the array as a direct function of the observation angle to give equivalent baselines for the observation.
So, yes, you can see in any direction around the Moon, but placement on the Moon is not a simple matter.
Consider that you don't want it pointing towards the sun either. Or, maybe you do. That's an interesting argument right there. You'll get data from the sun, but you'll also have periods where you have nothing *but* data from the sun. Similarly, Jupiter kicks out a lot of radio signals. A lot of design decisions end up still needing a fairly complex shield to make sure that you're getting only the radio waves you are searching for.
Arguably, you would want to place it near the lunar poles. Not for any of the BS arguments about the potential for water there, but because they have the least interference from Earth and the Sun. It also means you can survey the same stretch of sky for longer periods as out-of-plane bodies there are a lot easier to track and remain in the same cone of observation irrespective of the current lunar position. (ie, something that is at zenith over the lunar pole is not going to vary more than about 6 degrees from being overhead over the course of a year. Even something 25 degrees, or so, would still be visible pretty much all the time). If you go to lower latitudes, then it gets closer to a 14-day non-observation lineup followed by a 14 day period of variable observation from minimal to optimal and back as the object traverses the sky. The closer you get to the lunar equator, the more of the sky you will see, but the less the observation time and the more variable the quality of the observation.
Ideally, they design a small inexpensive setup which can be done a few times on various areas of the Moon. Just choosing one set of criteria is going to be interesting. This is not like Hubble which can be pointed in any direction. There are a lot of rocks in the way.
The moon's orbit is not perfectly circular, and its axis of rotation is not quite perpendicular to the plane of the orbit. Those effects combine to produce an apparent rocking motion, on a time scale of weeks, called libration. Thanks to that, we can see almost 60 percent of the moon's surface at one time or another.
rj
I particularly like the idea Imaging nearby Earth-sized worlds using large telescopes with multiple instruments and separate spacecraft to block the light from these exoplanets' host star (Webster Cash, University of Colorado, Boulder; David Spergel, Princeton University, N.J.). This seems very cool - the idea is that you put a big screen out in space to block the light of the host star, but not that of the star's planet. This is not a new idea - the problem is diffraction around the screen (occulter). But it looks like Cash and Spergel have found a design that minimizes the diffraction.
The cosmic microwave background left over from the big bang as measured by WMAP tells us the approximate age of the universe. Red-shift measurements tells us the distances of the stars we observe. The speed of light tells us how long it takes for the light of those stars to get here. Ta-da.
Or is this one of those "We are in the center of the universe" ideologies again?We ARE at the center of the universe. So is everywhere else. The Big Bang wasn't an explosion that filled out existing space from which there's a center. Space itself expands from that point on, so the same infinitesimal point where the big bang started is the place where you're standing in now. The standard analogy is the surface area of a balloon as you fill the balloon up. There's just no preferred center.
Warning: Opinions known to be heavily biased.
If done in the right way, this could be used to build infrastructure on the moon. It seems to me, that if we BUILD a radio telescope on the moon, then the same machinery used to build that will go into building other structures such as a regular scope. In addition, if this is outsourced to somebody like bigelow, they will use that as a means of constructing a lunar base.
I prefer the "u" in honour as it seems to be missing these days.
The current cosmological model of the Universe supposes that our position within the Universe is typical, not special. We are not located at the center of the Universe, but are rather taking part in its global expansion. I hope this answers your question.
Regards,
Padi Boyd
for the Ask an Astrophysicist HTH.
"The fight for freedom has only just begun." - Geert Wilders
The observatory does not have to be directly opposite the Earth. Just behind the edge would work. You could then run a fibre-optic cable to a location nearby that is visible to Earth.
Didn't Sagan want this before the end of the Millennium? Could have been done, too.
Fiat Homos et Pereat Theos