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Measuring The Distance From Earth To Moon

Posted by timothy on from the technical-challenges dept.

lewiz writes: "Tom Murphy at UW is attempting to measure the distance between the Earth and The Moon to the nearest millimetre according to this BBC News article. 'His tape measure will be a giant telescope at Apache Point in New Mexico. Retroreflectors left on the surface of the Moon by various space missions, including the Apollo 11 lunar landing, will also come in handy.'"

10 of 284 comments (clear)

  1. Oddly Enough... by CheshireCatCO · · Score: 4, Interesting

    ... according to my Solar Systems Dynamics textbook, we already know the rate at which the Moon is receding from the Earth: 1 nanometer/second. Which is, of course, a better precision than this group seeks to take on. But that measurement probably used the Doppler shift. It just goes to show that it's much easier to measure radial velocities than distances!

    1. Re:Oddly Enough... by Anonymous Coward · · Score: 1, Interesting

      1 nanometer/second. Which is, of course, a better precision than this group seeks to take on.

      Hmm, one significant digit isn't very precise. And significant digits are all that matters: any measurement in centimeter/year can be converted to nanometer/second (or to attometer/nanosecond, or to meter/century...) it's just a speed that is measured.

  2. Umm, the distance isn't constant by DeafDumbBlind · · Score: 4, Interesting

    The moon revolves around the earth in an eliptical orbit, not a circular one. Unless he's talking about getting the average distance.

    --


    Jesus used to be my co-pilot, but we crashed in the mountains and I had to eat him.
  3. 3.8 cm by niola · · Score: 1, Interesting

    Well, if the moon is moving 3.8 cm away from the Earth every year, that does not bode well for life on this planet next millennium. Since gravity is so important to our climate I would imagine that this could have bad long term effects.

    I remember reading something a while back about ancient Egyptians believeing there were two suns int he sky. I wonder if what they saw was a much closer moon back then?

    All throughout the Earth there is evidence of dramatic gravitational changes int he past. For example, below all the ice in the northern reaches of Canada there are vast reserves of coal. Since coal is made through the decay of organic matter, it means there had to be a massive forest up there at some time. Then in the deserts of Africa there are mountains where they find seashells like 1000 feet above sea level.

    Perhaps the moon pulling away from the Earth has caused many of the major changes on the Earth...

    --Jon

    1. Re:3.8 cm by Anonymous Coward · · Score: 1, Interesting

      According to stellar evolution models, the sun is about 10% brighter than it was 100 million years ago. I would think this to have a much stronger effect than a 0.5% stronger lunar tide.

  4. Re:My tax dollars at work... by pclminion · · Score: 3, Interesting
    The moon's orbit varies by far more than 1 millimeter all the time. There are all sorts of influences, including the earth's gravity, the sun's gravity, Jupiter's gravity -- as well as factors that will introduce error into the measurements, such as refraction of the laser in the earth's atmosphere.

    Therefore, by measuring the distance to an accuracy of a millemeter, we might be able to gain some insight about: earth's gravity, the sun's gravity, and Jupiter's gravity. The point of this experiment is not to know how far it is to the moon. The point is to better understand the moon's orbit, and the various influences which affect it.

  5. Another totally worthless experiments by trenton · · Score: 4, Interesting
    How about this one: build a clock that can be taken to sea. What good is that? We already have accurate clock on the shore. Oh, right, you can figure out your latitude. And, in the process, invent roller bearings and bimetallic strips, two extremely useful technologies, ones we weren't even trying to create. That turned out well for us, huh?

    The moon distance measurement is obviously good. It seeks to do something no one else has ever achived. Even if the results aren't interesting, the new techniques used are. Anyone that doesn't see its intrinsic value is shortsighted.

    --
    Too big to fail? Does that make me to small to succeed?
  6. careful, in another 100 million years... by supernova87a · · Score: 2, Interesting

    Lots of people seem to know that the moon is moving farther away from the earth, but did you know that the earth's rotation is slowing down?

    These two phenomena are actually related -- the orbital angular momentum that the moon is gaining (moving farther away) is taken from the earth's rotational angular momentum. Gradually, but measurably, the earth *is* slowing down. You might have heard of leap seconds? These are to compensate (partially) for the slowing in fact!

    Eventually (ok, in maybe 100 million - 1 billion years) the earth and moon will orbit/rotate at the same angular velocity, so that at that time, we will always see the same face of the moon, and the moon will always see the same face of the earth!

    Better pick which side of the earth you'll want to live on, otherwise if you pick wrong, you'll *never* be able to see the moon... :)

  7. Re:Reflectors on the moon? It's a lie !!! by laserjet · · Score: 3, Interesting

    I hate to ask... but, has anyone actually seen the video on moonmovie.com? I am wondering if it is any good or not.

    another question: don't we have telescopes good enough that we could see things that were "left" on the moon, like the lunar rovers, their boots and gloves, etc.? It would seem that would put the "did we really land on the moon?" controversey to rest....

    --
    Moon Macrosystems. Sun's biggest competitor.
  8. Re:Reflectors on the moon? It's a lie !!! by andycal · · Score: 2, Interesting

    I don't have a link, but I recall reading ( I think it was a FAQ from HBO's Earth to moon series) that the atmosphere limits image resolution to a point that it isn't possible to get an image from a land based telescope that will show the decent modules and lunar rovers left on the moon.

    I also suspect that orbiting telescopes can't be configured to focus so close. ( like trying to use binoculars to look at your hand)

    It does leave me wounding just how powerful the laser must be to be scattered by the atmosphere on the way up and the way back and still be visible.