You might want to retry that calculation with the
correct sun angles.
Thanks. See below.
Edit to add: DOH! Tunnel vision on the angles led me to miss the very good catches by Shrinker and CurtC, below. Taking a tangent on the angular difference is a whopper of an error.

riceless! Such confidence. First of all, who was talking about the flagpole? Not me, or Curt. Read my posts again. I don't know about anyone else, but I was looking at the shadow of the LM. It's moving much faster than the flag shadow since it's taller, but if you want to go for the shorter shadow because it helps your case then go ahead. I also suggested a shadow length to object height ratio of 2, so Curt was using 26.57 degrees as the angle of the sun. Guess you couldn't work that out so you went with your own numbers huh?
The shadow length to object height ratio that I've assumed is 1.75, which, as I wrote, equates to a Sun angle around 30 degrees. There was no guesswork involved; only the acknowldgement that this figure is approximate because the video camera wasn't placed perpendicular to the shadow direction. Seems Curt and I were pretty close to each other, albeit both wrong, but see later!
Second of all, 18mm!? Are you serious? What the heck was all that junk you typed?
If you read carefully I think you'll find I wrote
13mm, so you're only 46% out with this sloppy observation!
With your assumptions...
Shadow length with sun at 30 degrees above the horizon= 2.2m * tan(90-30) = 3,811mm
Shadow length with sun at 30.35 degrees above the horizon = 2.2m * tan(90-30.35)=3,757mm
Difference = 54mm
Unlucky.
Er ... I don't think luck has
anything to do with this, and here's the rub:
EVERYBODY QUOTED IN THIS POST (with the possible exception of PetersCreek, although I can't figure out why he hasn't pointed it out himself, if so!) IS MAKING THE GRAVE MISTAKE OF BELIEVING THAT THE ANGULAR ROTATION OF THE MOON EQUATES TO AN EQUIVALENT CHANGE IN SUN ANGLE. WRONG!!! THAT'S ONLY THE CASE WHEN OBSERVING THE SUN DIRECTLY OVERHEAD, I.E. FROM A POINT ON THE LUNAR SURFACE THAT'S PERPENDICULARLY TANGENTIAL TO THE DIRECTION OF THE SUN. Think about it: the lower the Sun angle, i.e. the closer the Sun is to the horizon, the more the rotation of the Moon is manifest in movement of an object on the lunar surface
DIRECTLY TOWARDS OR AWAY FROM THE SUN. Movement directly toward or away from the Sun has
ABSOLUTELY NO EFFECT on Sun angle! This would be most pronounced at a position on the lunar surface that is
tangentially parallel to the direction of the Sun, i.e. exactly on the 'top' or 'bottom' of the Moon with the Sun out at the 3 O'clock position (if you could still see the Sun then, which you can't as it's dropped below the horizon).
So, given that the Sun angle was only around 15 degrees, a 0.34 degree change in rotation of the Moon will result in a
MUCH SMALLER change in Sun angle!
If we assume 20 degrees at the start of the film then the difference over 40 minutes becomes a quite easily detectable 112mm.
Edit: and if we use 15 degrees, the difference is around 200mm
But it's a shame these figures are hopelessly wrong! Intuition alone should inform you that for an equivalent period of only
83 seconds on Earth you shouldn't really be able to detect the rotation of the Moon by observing changes in a 22m-long shadow from a distance!
You can't calculate just the tangent of 0.34 degrees to get the change in the lengths of the sides! The tangent function is very non-linear.
I'm not sure you're sure what I did. I did the equivalent calculation that you've done hereunder, but without the error that you've made:
I did the calculations according to Shrinker's conditions: that the shadows are twice as long as they are tall, and that the LM is 6 m tall. So I was figuring how far the top of the LM's shadow will move. I'll review that here.
If the shadow is twice as long as it is tall, that's an angle of 26.57 degrees (atan(0.5)). The LM is 6 m tall, the shadow is 12 m long. I agree with your 0.34 degrees in 40 minutes figure, so at the end, the Sun's angle will be 26.90 degrees. For the 6 m LM, its shadow will now be 6/(tan(26.90)), or 11.82 m. Before, it was 12 m, so it moved by 18 cm.
No - see above. You've woefully over-calculated the change in Sun angle.
Nice tone. But if you do the same calculation with a 2.2 m flag pole, you get that it moved by 6.4 cm, not 1.3.
See above!
Maybe you can check your calculation to identify where you've gone wrong. Oh wait, I already did that for you - you assumed that the tangent function was linear, that it would change the same amount in going from 0 to 0.34, as it would from 26.57 to 26.90. (Note that the last figures look like they changed by 0.33 instead of 0.34, but I carried the calculations out with more significant digits and rounded off here).
Not sure what you mean here. I calculated the length of the flagpole shadow as a function of the Sun angle (Tan 30 degrees) and the height of the flagpole (2,200mm), assuming the flagpole to be planted vertically. Do you believe there's something wrong with that?
Math is not my strong suit so I am just going to address your initial assumptions.
The sun angles for the Moon missions are listed here:
http://www.hq.nasa.gov/pao/History/alsj/alsj-sunangles.html
If the video you are refering to is from the Apollo 11 mission then the starting and ending sun angles are :
Apollo 11
Landing: 102.75 GET
EVA
Start: 109.00 GET, 14.0 deg.
Finis: 111.75 GET, 15.4 deg.
edited: Damn! Peters beat me too it.
Your 30 degree estimate seems a bit too generous by a factor of 2. And as you can see the angles shift by 1.4 degrees during the whole mission.
http://www.cs.indiana.edu/sudoc/image_30000061709352/30000061709352/pdf/11post.pdf
According to the above mission report briefing the flag pole was 8 ft tall or 2438.4 milimeters. Not bad. you even got the eight inches to account for the part embeded in the soil.
Try running the numbers with the corrected sun angles.
See below.
Now if you could be off by a factor of 2 for the sun angles by making an estimate based on an image. How about Groves? Think he might be off on one or two things?
Let's review this statement when we're all agreed on the change in shadow lengths, shall we!
Which mission and day was this? I think it was Apollo 15, and if they just put the flag out, that would be the first day, right? In that case, the Sun's angle was around 20 degrees, and the shadow of the top of the flag pole would move by 11 cm in 40 minutes.
Also, you could consider the tangent of just 0.34 degrees, but you'd need to apply that to the distance from the flag pole's top, to the shadow of the flag pole top, not just the height of the flag pole. I'm not sure which is the way Southwind was trying to do it, but either way he made an error that throws his answer way off.
I don't think I did, as described above.
Hey Southwind, Do you think Dr. Groves might have made a similar error in his calculations?
A similar error to you lot, is that?!
OK, let's re-run the calculation with the correct sun angle and for the LM shadow instead of the flagpole:
Assumptions:
Sun angle above horizon = 15 degrees.
LM is approximately 6,000mm tall.
LM stands vertically.
Axis of Moon's rotation is perpendicular to the direction of the shadow, i.e. the shadows will simply elongate and shorten.
Calculations:
First, using trogonometry, let's calculate the length of the LM shadow; call it 'X':
X = 6000mm / Tan 15 degrees = 22,392mm
Now, using triangulation, let's calculate the angle formed by the vertical axis of the LM and an imaginary line running from the top of the LM to the tip of the shadow on the lunar surface; call it 'Y':
Y = 180 degrees - 90 degrees - 15 degrees = 75 degrees
Now, let's calculate the angle of rotation of the Moon over the duration of the video, namely 40 minutes:
40 minutes / (29.5 Earth days x 24 hours x 60 minutes) x 360 degrees = 0.34 degrees
So, after 40 minutes the Moon will have rotated about its axis by 0.34 degrees. In other words, the LM will have rotated from the vertical 90-degree position to either 89.66 degrees or 90.34 degrees, depending on which direction the Moon is rotating in relation to the Sun (think of it like a hand on a clock moving away from the 12 o'clock position by 0.34 degrees in either direction).
This rotation or 'tilting' from the 'vertical' results in an apparent reduction in the height of the LM from the lunar surface, which will manifest itself as a shortening or lengthening of the shadow. If the LM 'tilts'
towards the Sun the shadow length will tend towards zero as the 'tilt angle' approaches 15 degrees (i.e. between the two and three o'clock position, with the LM top pointing directly at the Sun). If the flagpole 'tilts'
away from the Sun the Shadow length will initially lengthen as the LM tend towards a 75-degree tilt (i.e. between the 11 and 12 o'clock position, at which point the LM will be perpendicular to the 15-degree Sun angle). Thereafter, the shadow length will shorten as the LM angle tends towards 0 degrees (the 9 o'clock position), at which point there is no shadow!
So, the question is, what does a rotation of the Moon, or 'tilting' of the LM, by 0.34 degrees equate to in a shortening or lengthening of the shadow length? Let's calculate it:
As the light from the Sun can be considered to be travelling in parallel 'rays' the shortening of the shadow length will equate to the horizontal distance that the top of the LM moves from its original position; call it 'Z'. This can be calculated thus:
Z = Tan 0.34 degrees x 6000mm = 36mm.
So, 36mm appears to be the
maximum 'movement' of the shadow across the lunar surface.
OK, a slightly greater movement than the flagpole shadow, but I'll ask again, which of you are going to try to convince me that you can detect a 36mm movement (that's less than the diameter of a golf ball!) of the tip of the LM shadow across the lunar surface from watching the linked video?!