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AJ
2001-Dec-10, 05:48 PM
I keep reading that it would a great thing to get a telescope on the darkside of the moon. I guess I find it hard to believe that there is a side of the moon that never gets light via the earth or the sun. Is this really possible?


-AJ

Wiley
2001-Dec-10, 05:52 PM
BA's misconceptions page answers this question:

http://www.badastronomy.com/bad/misc/dark_side.html



<font size=-1>[ This Message was edited by: Wiley on 2001-12-10 12:52 ]</font>

GrapesOfWrath
2001-Dec-10, 05:55 PM
Any portion of the moon that faces the Earth will either be getting strong earthshine (and the Earth look to be 16 times the moon area we see) or you'd be in strong daylight. So, the best place for an observatory (for the half of each month that it is dark) is the back side of the moon.

One definition of dark, in my Ame. Her. Dic., is "8. Concealed or secret; mysterious: 'the dark mysteries of Africa and the fabled wonders of the East' (W. Bruce Lincoln)." In that sense, the back side of the moon is the dark side.

Ben Benoy
2001-Dec-10, 06:08 PM
But while it would be very dark there, it would also have large swings in temperature, which is bad for precision instruments. Although I suppose you could put your happy cool telescope under a reflective blanket when it's sunny outside, and only take it off when its overcast, but what good is a telescope when it's cloudy out?

Also, you'd have to store up a lot of power during the day time to make this worthwhile. Otherwise, you'd run out of juice and be stuck in the cold for two weeks, and nobody wants that.

Ben Benoy

GrapesOfWrath
2001-Dec-10, 07:30 PM
On 2001-12-10 13:08, Ben Benoy wrote:
But while it would be very dark there, it would also have large swings in temperature, which is bad for precision instruments. Although I suppose you could put your happy cool telescope under a reflective blanket when it's sunny outside, and only take it off when its overcast, but what good is a telescope when it's cloudy out?
I'm thinking...a dome. And Ben, it doesn't get overcast on the moon much. That's one of the advantages. /phpBB/images/smiles/icon_smile.gif

ToSeek
2001-Dec-10, 08:17 PM
There should be places on the Moon that never see sunlight, near the poles. Conveniently, if there's any water on the Moon, this is where it will be!

GrapesOfWrath
2001-Dec-10, 09:15 PM
You mean, like in caves, or depressions in the rock?

Donnie B.
2001-Dec-11, 12:10 AM
The word you're looking for is craters.

Ben Benoy
2001-Dec-11, 01:40 AM
I don't know what you guys are talking about, but around here water comes in bottles. Is that what you mean, bottles of water on the moon?

Seriously, how much surface area could there be which was dark all the time? I don't think it's very big, since if there were no craters, there would be no dark spot at all. This just sounds fishy...

Ben

Chip
2001-Dec-11, 06:01 AM
I like the idea of an automated lunar telescope, though for right now, a space telescope in Earth orbit is more practical and a bit easier to service.

Also appealing from an engineering and aesthetic viewpoint is Dr. Frank Drake's proposal to use natural small circular craters for foundations for future Arecibo style lunar radio telescopes. The lunar surface has a lot of really nice dish shaped impact craters. This would save on construction costs.

P.S. Arecibo's wed site: http://www.naic.edu/

Whoops - almost forgot to mention that there are spots on the moon that are dark for long periods if not forever, within craters at the lunar poles.

Chip

<font size=-1>[ This Message was edited by: Chip on 2001-12-11 14:21 ]</font>

ToSeek
2001-Dec-11, 12:38 PM
On 2001-12-10 20:40, Ben Benoy wrote:
Seriously, how much surface area could there be which was dark all the time? I don't think it's very big, since if there were no craters, there would be no dark spot at all. This just sounds fishy...


"The only possible way for ice to exist on the Moon would be in a permanently shadowed
area. The Clementine imaging experiment showed that such permanently shadowed areas do exist in the bottom of deep craters near the Moon's south pole. In fact, it appears that approximately 6000 to 15,000 square kilometers (2300 to 5800 square miles) of area around the south pole is permanently shadowed."

from http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html

SeanF
2001-Dec-11, 12:40 PM
On 2001-12-10 15:17, ToSeek wrote:
There should be places on the Moon that never see sunlight, near the poles. Conveniently, if there's any water on the Moon, this is where it will be!


I don't think so -- I believe the Moon's orbit around the Earth is slightly tilted relative to the ecliptic (5 degrees?), so I think even the poles would get some sunlight, but the sun would be low in the sky.

Of course, the lack of atmosphere on the moon means the light doesn't get bounced around like it does here -- I would think even with the sun above the horizon, you'd still be able to see stars and what-not in the other part of the sky . . .

ljbrs
2001-Dec-12, 01:37 AM
Since the dark side will be changing continuously during the Lunar month, it would not be an advantageous place to have any kind of stationary observatory. It would be much better to have a robotic satellite which itself can rotate. Do not forget that you need to talk a whole lot of people into paying for anything you would like to see. This means educating a large section of the public in a way that has never happened before. The public is fickle and has a very short attention span. Look at what happened with the Apollo program. The public lost interest pretty fast. The public is pretty stupid/ignorant when it comes to anything scientific.

Of course, there is no "dark side" of the Moon. However, there may be darker areas at the poles wherever there are craters in those positions.

Regardless, the public will never let anything so expensive happen.

ljbrs /phpBB/images/smiles/icon_frown.gif /phpBB/images/smiles/icon_rolleyes.gif

Kaptain K
2001-Dec-12, 06:24 AM
"there is no dark side of the Moon. Matter of fact, it's all dark"
Pink Floyd

gbaikie
2001-Dec-12, 06:53 AM
On 2001-12-11 07:40, SeanF wrote:


On 2001-12-10 15:17, ToSeek wrote:
There should be places on the Moon that never see sunlight, near the poles. Conveniently, if there's any water on the Moon, this is where it will be!


I don't think so -- I believe the Moon's orbit around the Earth is slightly tilted relative to the ecliptic (5 degrees?), so I think even the poles would get some sunlight, but the sun would be low in the sky.

Of course, the lack of atmosphere on the moon means the light doesn't get bounced around like it does here -- I would think even with the sun above the horizon, you'd still be able to see stars and what-not in the other part of the sky . . .



Here's ref about how lunar polar craters are in permenent darkness:
http://www.psrd.hawaii.edu/Dec96/IceonMoon.html
And at lunar poles you have both sunlight and darkness. If you are high enough [top of tall mountain] you can have nearly continuous sunlight and in a crater you can have continuous darkness- though you would have starlight. The area of total darkness would be thousands of sq miles.
-gb

Bob S.
2001-Dec-14, 05:49 PM
Okay, so there are parts of the moon that are in total perpetual darkness that are freakin' huge. But it kind of limits your angle of view, no?
Since any telescope would have to be manufatured on Earth anyway, why not make it another Hubble, but put in orbit at L-4 or L-5 near the moon rather than on it. You wouldn't need to spend on braking fuel to land the components on the surface, you wouldn't have to drive pylons and pour a foundation for equipment and facilities on the lunar surface. And you would have unlimited angle of view of the entire sky (except for the direction of the sun, Earth, and the moon).

{wishful thinking}
And it could be a driving force for justifying the construction of orbital habitats a la 2001's big wheel space station.

ToSeek
2001-Dec-14, 06:07 PM
On 2001-12-14 12:49, Bob S. wrote:

Since any telescope would have to be manufactured on Earth anyway, why not make it another Hubble, but put in orbit at L-4 or L-5 near the moon rather than on it.



The Next Generation Space Telescope (http://ngst.gsfc.nasa.gov/) is going to be located at the Sun-Earth L-2 point (i.e., permanently in the shadow of the earth).

GrapesOfWrath
2001-Dec-14, 06:37 PM
On 2001-12-14 13:07, ToSeek wrote:
The Next Generation Space Telescope (http://ngst.gsfc.nasa.gov/) is going to be located at the Sun-Earth L-2 point (i.e., permanently in the shadow of the earth).
Cool. But it won't be in the umbra, right? Isn't the L2 point 1.5 million km from Earth? That makes the Sun have about 8% more angular diameter than the Earth, at that distance. It'd see a permanent annular eclipse--with more light than this afternoon's annular eclipse.

ToSeek
2001-Dec-17, 02:50 PM
On 2001-12-14 13:37, GrapesOfWrath wrote:
Cool. But it won't be in the umbra, right? Isn't the L2 point 1.5 million km from Earth? That makes the Sun have about 8% more angular diameter than the Earth, at that distance. It'd see a permanent annular eclipse--with more light than this afternoon's annular eclipse.


Not sure. The MAP website (http://map.gsfc.nasa.gov/m_mm/ob_tech1.html) indicates that the chief advantage of the L2 point is that the Sun, Moon, and Earth are all in the same direction, so that appears to be the justification rather than the permanent eclipsing of the sun.

I also noticed that MAP won't be at the L2 point but will be in an orbit around it, so it's even less likely to be shaded.

(I use MAP as an example because it and NGST will be similarly located.)


_________________
"... to strive, to seek, to find, and not to yield." - Tennyson, Ulysses

<font size=-1>[ This Message was edited by: ToSeek on 2001-12-17 09:53 ]</font>

GrapesOfWrath
2001-Dec-21, 01:11 PM
On 2001-12-17 09:50, ToSeek wrote:
I also noticed that MAP won't be at the L2 point but will be in an orbit around it, so it's even less likely to be shaded.
The MAP Trajectory and Orbit (http://map.gsfc.nasa.gov/m_mm/ob_techorbit.html) page says that the lissajous orbit around L2 is such that the Earth vector is between 1 and 10 degrees off the Sun-Earth vector--so the Earth will never eclipse the Sun. It even seems to say that they want to avoid eclipses. Perhaps the sudden difference in temperatures would cause problems.

The NGST orbit info (http://ngst.gsfc.nasa.gov:80/project/text/orbits.html) just refers to the MAP pages.
_________________
rocks

<font size=-1>[Added NGST link]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2001-12-21 08:17 ]</font>

Wally
2001-Dec-21, 05:03 PM
What's the affect of the moon on the earth-sun L2 point? If it's unstable to begin with, I would think something with 1/4 the mass of one of the principle players would render L2 (as well as L1) so unstable as to be useless. Is the distance between the L points and the moon great enough as to where this isn't the case?

GrapesOfWrath
2001-Dec-21, 05:40 PM
On 2001-12-21 12:03, Wally wrote:
What's the affect of the moon on the earth-sun L2 point? If it's unstable to begin with, I would think something with 1/4 the mass of one of the principle players would render L2 (as well as L1) so unstable as to be useless. Is the distance between the L points and the moon great enough as to where this isn't the case?
The mass of the moon is only 1/81 that of the Earth, not 1/4. Its radius is about 1/4 that of the Earth's.

L2 is not going to be useless, since it seems that MAP and NGST will use it. The L4 and L5 points are 1 AU away from the Earth, but no asteroids have ever been found there, although Mars has some, so maybe there is some sort of long term effect.

Wally
2001-Dec-21, 06:34 PM
Thanks for the correction GoW. I realized after I posted that I was incorrect in saying mass rather than size, but got caught up in actual work stuff before I could correct.

I agree it's not useless, as we are/will be using it. Guess I was just wondering if anyone knew what affect the moon had on the stability of L2 (if any) as opposed to a moonless planet/sun L2 point. I almost wonder if it might not make it more stable. . . kind of like giving a top an extra spin every 28 days or some such thing.

GrapesOfWrath
2001-Dec-21, 06:44 PM
Hmmm. Where is the Earth/Lunar L2? That would have to make a monthly spin under the Earth/Solar L2, right?

According to my rough calculations, the lunar L1 is 58,000 km this side of the moon, and L2 is 65,000 km on the other side. About a sixth of the distance between the moon and Earth.

<font size=-1>[Added calculations]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2001-12-22 08:34 ]</font>

2001-Dec-27, 01:08 AM
On 2001-12-10 13:08, Ben Benoy wrote:
But while it would be very dark there, it would also have large swings in temperature, which is bad for precision instruments. Ben Benoy

Actually, I can see an advantage of the hidden side of the moon with radio telescopes. Much of the background that interferes with radio astronomy comes from electrical stuff on the earth. I believe that some of this stuff would even interfere out to the moon's orbital radius. However, the moon would block this electromagnetic crud.

The moon would block radio waves that come from the earth. The temperature swings that you talk about would affect a radio antennae less than an optical lens. The surface would provide support for a very stable antennae, as compared to an orbital antennae that could precess or have all sorts of unwanted motions. One could even do pretty good astronomy with wavelengths from centimeters to kilometers scale.

Maybe now that Luna is going to be a Chinese province. I am sure they will want some legitimate front to put in the underground missile silos. By the way, is anyone else frightened by China going to the moon?
/phpBB/images/smiles/icon_eek.gif

<font size=-1>[ This Message was edited by: Rosen1 on 2001-12-26 20:09 ]</font>

gbaikie
2001-Dec-27, 09:56 PM
"Maybe now that Luna is going to be a Chinese province. I am sure they will want some legitimate front to put in the underground missile silos. By the way, is anyone else frightened by China going to the moon?"

From a sub-orbital trajectory any place in the world can be hit in less than an hour- from the Moon a missle would take days to get to a target. Any missile silos on the Moon would not be a threat in terms of first strike capablity (in a worldwide nuclear war it would be "over in about an hour from start to finish"). Missile silos on the moon would act as a strong deterrant (if one country had military control over the Moon) because the Moon could offer a strong defensive postion. Though instead of missiles you probably would use lasers (one valuable aspect of the Moon is being a location to have solar farms and this electrical energy could power lasers as easily as powering factories). Of course lasers would have "first strike capability", they could hit most satellites most of the time all the time. And lasers could hit anywhere on Earth surface as it rotates once per day.
Though this might work in theory, I don't really think this is much of a threat- though it could threaten any long terms goals of US global domination.

jkmccrann
2005-Oct-27, 08:02 AM
But while it would be very dark there, it would also have large swings in temperature, which is bad for precision instruments. Although I suppose you could put your happy cool telescope under a reflective blanket when it's sunny outside, and only take it off when its overcast, but what good is a telescope when it's cloudy out?

Also, you'd have to store up a lot of power during the day time to make this worthwhile. Otherwise, you'd run out of juice and be stuck in the cold for two weeks, and nobody wants that.

Ben Benoy

It would seem that something on the far side of the moon would be an ideal place to be solar-powered and to store up that energy during those times when the Sun was visible.

Ken G
2005-Oct-27, 12:42 PM
What about shielding the electronics from the hazards of space? Power grids in Canada get knocked down by solar flares from time to time, and they get some protection from Earth's magnetic field.

pghnative
2005-Oct-27, 05:31 PM
The solution is obvious --- no Canadian electrical engineers are to work on the project. :lol:

eburacum45
2005-Oct-28, 08:10 AM
"there is no dark side of the Moon. Matter of fact, it's all dark"
Pink Floyd

Hmm- I've always wondered if that was bad astronomy, or just a pedantic joke.

1/there is no permanently dark side of the Moon
but
2/ it patently isn't all dark, as half of it at any one time is lit by brilliant sunshine, somewhat brighter than on earth.
but
3/any part of the Moon will be dark at some point during the Lunar Day, so in fact it is all dark, just not constantly so
and
4/the Moon's albedo is very low, and it would certainly look dark if you brought a small peice of the Moon to earth-say a metre square; it would look dark grey, like an asphalt road surface. So yes, it is 'all dark' in that respect.

Oh, yes- there might be small regions of the Moon at the poles which are permanently illuminated; these locations would be a good place to put solar power collectors...

sidmel
2005-Oct-31, 02:42 PM
Actually there is a Dark Side of the Moon: Circa 1973, Pink Floyd :)