Talk:Apache Point Observatory Lunar Laser-ranging Operation

message: The author of the project web page on APOLLO (Tom Murphy) has given permission to use that web page, and the introductory papers, to create the Wikipedia article on APOLLO. LouScheffer (talk) 05:45, 27 January 2008 (UTC)
thread_title: source

message: It would be interesting to tell the length of the pulse and how many photons are in a pulse.  I don't think the article says.  Bubba73 (You talkin' to me?), 16:38, 6 June 2010 (UTC)
replies: text: 100 ps.  Bubba73 (You talkin' to me?), 21:02, 12 June 2010 (UTC)
thread_title:  pulse length 

message: Wondering if anyone has an idea as to the actual exerted solar radiation pressure on the surface in approximates by the month? Aditya.m4 (talk) 02:29, 3 September 2011 (UTC)
thread_title: Radiation pressure exerted on the moon's surface

message: Hi, in the section "Principles of operation" we can see the "Graph of returned photons".
So, obviously, 46 nano secs +/- 1 nano sec is not the time photons need to make the trip back to Earth (more around 1.3 sec) nor the time to make the round trip (more around 2.6 secs).
The time-scale on the x axis is counted in minutes so no chance to read 1.3 sec or 2.6 secs there: it's definitely more the timeline of the sequential burst events (or call it whatever better name you can find, certainly).
On the y axis we can read "Time into gate": is it the telescope-side dead-time into gate photon-detection limitation? Or is it the time spent in corner cubes on the Moon? Or is it just the deviance from either the average travel time or theoretical travel time (but then why no minus values on the y axis?)...?
On another Wikipedia article "Third party evidence for Apollo Moon landings" we find the same graph (same date 8 December 2005) with a -less- vague explanation that tends to let me, the layman reader, think that the nano secs have something to do with the average diameter of the reflecting target on the moon... The thing is, dimensions of the mirrors (an example at 0.6m² so less than 1m average diameter) don't match the travel distance of light in 46 +/-1 nano secs (13.8m +/- 0.3m) where the black lines shows up. But the 120 nano secs (at the top of the y axis) do match the 30 meters "range of the plot" (of the y axis). Confusing, except for professionals actually working with those graphs I guess...
In conclusion, I think this particular graph needs a little more explanations than to date, who agrees?
Or at least a link to a better explanation, either a better-than-now "Third party evidence for Apollo Moon landings" article (section "Retroreflectors) or a -currently even more vague- "Lunar Laser Ranging experiment" article (right now split-up between the top-page "Principles" section and the bottom-page "Gallery")... Right? 80.215.128.255 (talk) 14:03, 11 January 2023 (UTC)
replies: text: OK, I gave this a try.  Feel free to improve/comment.  LouScheffer (talk) 14:42, 13 January 2023 (UTC)
replies: text: Thank you very much for the fast answer & added explanation in the article! It's a little bit clearer now for me (and other laymen I guess), especially the specific meaning of "gate" in this context. I ... just think there is a contradiction about the span/range of the y axis: the Wikipedia article "Third party evidence for Apollo Moon landings" gives it a range of 30 meters (also 120 nano secs, exact same graph). And yes 120 nano secs is the time needed for light to travel 30 meters in total vacuum. Now thanks to you I also understand the light travels probably exclusively through air during this "y-axis time" (and maybe some refractive optics?), so this could explain a shorter range because of the slower effective speed of light in non-vacuum medium (waow v~=0.6c ?? That's a lot of refractive optics -or few but very strong ones, I'm guessing a lot of chromatic aberrations on a full visible-spectrum image coming out of this telescope wich is ... surprising). Sorry for being picky, I'm just confused, and again, great work explaining the "gate" thing! Thanks a lot! :) 87.88.145.236 (talk) 14:52, 14 January 2023 (UTC)
replies: text: 18 meters is correct, and I fixed this on 'Third party' page.  120 ns times speed of light (300,000 km/sec) is 36 meters.  But that corresponds to 18 meters in range, since the light needs to go both ways.  LouScheffer (talk) 15:10, 19 January 2023 (UTC)
thread_title:  Dead-time into gate or time spent in corner cubes or size of the reflecting object?