Moon Distance

[dkaakd]

I remeber reading a while back that one of the lunar missions placed a mirror on the moon's surface so an Earth-based laser could be used to make measurements.<br /><br />Does anyone know of a link to this data?<br /><br />Thanks,<br /><br />Dave

 

[dkaakd]

Thanks CE.<br /><br />In my research I also found a couple of good articles if anyone else is interested.<br /><br />http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/ApolloLaser.html<br /><br />and <br /><br />http://www.lpi.usra.edu/expmoon/Apollo11/A11_Experiments_LRRR.html<br /><br />Dave<br />

 

[cpuguy1]

Okay ... I have seen the 3 links ... where is the distance these projects are so called looking for, to these acurate distances?<br />One said it refined to the inch<br />One said accuracy of about 3 centimeters<br />Another said an accuracy of about 3 centimeters also ... then later on the page reports a distance 'ABOUT' 385,000 kilometers. No decimal with more numbers.<br />I would like to see some numbers? Full written out, out to the 6th or 7th digit after the decimal place in kilometers, give or take 3 cm.<br /><br />Or is the full written out length classified?<br /> <div class="Discussion_UserSignature"> <p><font size="2">The polarization of the alpha wave's primary phase of the modified parallel cross section of your brain will confirm you are not thinking up to your potential.  -  </font><font size="2">Professor West</font></p> </div>

 

[rhodan]

Well, since an inch is 2.54 centimeters, and 2.54 centimeters is about 3 centimeters, the articles you listed don't quite contradict each other. Also the distance to our Moon varies; it's orbit is far from a perfect circle.

 

[CalliArcale]

Yep; the uncertainty is less a matter of poor precision than it is meant to be reflective of the average altitude of the Moon. The orbit has an eccentricity of about 0.05 (0 is a perfect circle). The moon actually changes measureably in apparent size as viewed from the ground on Earth over the course of a month, as it approaches and recedes. The effect is very obvious in this picture from Astronomy Picture of the Day: Apogee Moon, Perigee Moon . <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Leovinus]

Hey, I like that apogee/perigee picture. I've never seen that before. <div class="Discussion_UserSignature"> </div>

 

[nexium]

Perhaps someone can give us the distance to twenty significant digits for a recent perigee and a recent apogee. Even these will change minutely due to CME = corronal mass ejection and due to Jupiter, Mars and Venus positions. Neil

 

[CalliArcale]

Too minutely to be detected, I suspect. CMEs don't have much substance; they don't even really affect the trajectories of spacecraft (except indirectly, by screwing up their electronics and possibly causing them to miss their maneuvers, or by affecting the density of the Earth's atmosphere temporarily, altering the amount of drag they experience -- neither of these are relevant for the Moon). And the gravitational influence of even mighty Jupiter is negligible. So although the points might wobble slightly, I don't think you'd notice it execpt over a long time, and then the effect will probably be overwhelmed by the gradual recession of the Moon. On the other hand, irregularities in the Earth's gravitational field might have an effect; the Earth isn't totally uniform, after all.<br /><br />Yes, the Moon really is receding. This is due to a transfer of momentum from the Earth's rotation to the Moon's revolution. The Earth's rotation slows (enough that timekeepers must occasionally add a leap second to atomic clocks for official timekeeping purposes) and the Moon's orbital period increases as it moves further away. Eventually, if the solar system lasts long enough, the Earth's rotation and the Moon's revolution will be the same period -- the two bodies will be mutally synchronous, just like Pluto and Charon. There won't be any more total solar eclipses, but total lunar eclipses will last longer and the Moon will be bizarrely fixed to a point in the night sky, visible from only one hemisphere of the Earth. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>