The 4 hour picture of the earth by Apollo11

[benparry]

Evening all. In a FB group they have posted the picture of the earth taken by Apollo 11 after 4 hours into the trip. A hoaxy has suggested that after 4 hours they would still have been in LEO and with a 60mm focal length camera they couldn’t have captured it. I’m not sure of the focal length of the lens used to capture that picture but I’m sure they were out of LEO after just shy of 4 hours wernt they

[Allan F]

Since the parking orbit used before TLI was very low - about 150 km - there was still significant drag, and they had to burn out of there before too much velocity was lost, and they went into the denser parts of the atmosphere. So as I look at "Apollo by the Numbers", Apollo 11 entered Earth Orbit at 0h 11min elapsed, and started their TLI at 2h 44min. That's about 1.5 Earth orbits at that altitude.

The rest you can get here: https://history.nasa.gov/SP-4029.pdf

[onebigmonkey]

Which photo are they claiming is at 4 hours?

The magazine in use during EPO and post-TLI was then was magazine 36, which is recorded as using an 80mm focal length until AS11-36-5333, after which it was 250mm.

At 4 hours they were on their way and doing the docking and extraction of the LM.

The first remotely full Earth image (though partially obscured by the window frame) wasn't taken (according to my esitmates) until 18:15 UTC, around 04:42 hours in to the mission.

https://history.nasa.gov/alsj/a11/a11.photidx.pdf

See my estimates here:

http://onebigmonkey.com/apollo/CATM2/A11/01/a11_day01.html

[onebigmonkey]

A quick bit of googling suggests that the photo in question suggested at 4 hours is the same one I'm putting at 45 minutes later.

The image is one of a sequence taken after docking with the LM, which didn't happen until 3:24 MET, with extraction at 04:17 into the mission.

The photo's after this sequence are of an empty and distant S-IVB. A separation burn from the S-IVB took place at around 04:40.

I've assumed that the Earth photos were taken after that burn, but I'm happy to be corrected on that. The AFJ certainly puts the Earth photos earlier than I do.

Either way, at 4 hours in they were on their way to the moon!

[benparry]

https://www.facebook.com/photo/?fbid=200895626356771&set=a.112057551907246&comment_id=885546469790863&reply_comment_id=783452810252900&notif_id=1697482078484745&notif_t=feed_threaded_comment_reply&ref=notif

This is the FB link and the picture is the title picture. I assume this is the same pic you have OBM.

So basically his comment about them being in LEO is nonsense

[onebigmonkey]

Yes that's the same photo (AS11-36-5326).

It comes after the LM docking so it can't be in LEO!

My initial timing estimate was on the assumption it was taken immediately before the photo of the distant S-IVB, but I decided it could have been just after docking, so I've modified my text on the page above.

It certainly wouldn't have been possible to capture that much of the Earth's disk in a single image, as shown by the photos that actually were taken in the Earth Parking Orbit.

I see that thread's participant's are busy trotting out the same old cliches about the blue marble not showing enough of Earth (really easy to replicate with Google Earth) and them never showing the Earth on TV from the lunar surface (they did, several times). Just as well they do their own research, eh?!

[benparry]

Yes that's the same photo (AS11-36-5326).

It comes after the LM docking so it can't be in LEO!

My initial timing estimate was on the assumption it was taken immediately before the photo of the distant S-IVB, but I decided it could have been just after docking, so I've modified my text on the page above.

It certainly wouldn't have been possible to capture that much of the Earth's disk in a single image, as shown by the photos that actually were taken in the Earth Parking Orbit.

I see that thread's participant's are busy trotting out the same old cliches about the blue marble not showing enough of Earth (really easy to replicate with Google Earth) and them never showing the Earth on TV from the lunar surface (they did, several times). Just as well they do their own research, eh?!

Correct

What i've noticed now, with a lot of people, is it's the Flat Earthers not actually mentioning at the start that they are Flat Earthers and just questioning the landings. I bring up my usual fav questions - Movement of Dust and Tracking of the vehicles - and it quickly turns to 'I bet you believe we live on a spinning ball too'. There is a comment on the same thread from a US guy.

[onebigmonkey]

Often followed swiftly by 'you sound vaxxed' 

[benparry]

Often followed swiftly by 'you sound vaxxed' 

Ha ha yes. I have had 214 jabs apparantly.

[Peter B]

I've found the Lunar and Planetary Institute website useful for Apollo photograph chronology: https://www.lpi.usra.edu/resources/apollo/catalog/70mm/

It shows thumbnails of all the Apollo photos, by mission and by magazine, in chronological order, along with their individual codes.

In the case of the photo in question, the magazine was used for: 2 photos inside the CM, 17 photos of the Earth in LEO, 7 photos of LM docking, then 10 photos of the Earth clearly post-TLI. 5326 is the last of the 10, and arguably the best of them.

Personally, I like the way the LPI's format allows each magazine to tell its own story, and the narrative of this magazine is pretty clear about where 5326 was taken.

[benparry]

I've found the Lunar and Planetary Institute website useful for Apollo photograph chronology: https://www.lpi.usra.edu/resources/apollo/catalog/70mm/

It shows thumbnails of all the Apollo photos, by mission and by magazine, in chronological order, along with their individual codes.

In the case of the photo in question, the magazine was used for: 2 photos inside the CM, 17 photos of the Earth in LEO, 7 photos of LM docking, then 10 photos of the Earth clearly post-TLI. 5326 is the last of the 10, and arguably the best of them.

Personally, I like the way the LPI's format allows each magazine to tell its own story, and the narrative of this magazine is pretty clear about where 5326 was taken.

Nice one cheers Peter

[Kiwi]

Yes that's the same photo (AS11-36-5326).

The Apollo 11 Flight Journal has some useful information about that photo, including that it was probably taken a few minutes prior to four hours Ground Elapsed Time (GET not MET for Apollo).

https://history.nasa.gov/afj/ap11fj/03tde.html

003:53:05 Armstrong: And Houston, you might be interested that out my left-hand window right now, I can observe the entire continent of North America, Alaska, over the Pole, down to the Yucatan Peninsula, Cuba, northern part of South America, and then I run out of window.

003:53:27 McCandless: Roger, we copy.

Long comm break.

That was Neil Armstrong with that report.

It is at about this point that a crewman, probably Neil given that he has just mentioned the view, takes two photographs of Earth half obscured by the structure of the Lunar Module.

AS11-36-5325 - Partial view of Earth behind the Lunar Module showing the US and Canada on the left, Greenland at the top, Western Europe and North Africa on the far right. Image by LPI

The second of these images shows enough of Earth's globe that a measurement can be taken to determine the distance to Earth at that moment. The calculation yields a value of about 18,700 km or 10,100 nautical miles. This calculation is the reason the image has been placed at this point in the journal.

AS11-36-5326 - Partial view of Earth behind the Lunar Module, taken at a distance of about 18,700 km or 10,100 nautical miles. It shows the US and Canada on the left, Greenland at the top, Western Europe and North Africa on the far right. Image by LPI

Although this image of Earth is incomplete, there is enough of the globe to allow a measurement to be taken across from limb to limb. A little analysis, including a few assumptions, then permits us to make an approximate calculation of the spacecraft's altitude when the photo was taken. By checking another high resolution scan from this film (in this case, AS11-36-5306 on mag N, scanned by JSC), the full height of a scanned frame was found to be 4,169 pixels. This represents 55.5 millimetres, the actual height of an image to the edge of the gate as measured on a negative from my contemporary Hasselblad 500C camera. This camera is of the same type and from the same era as the camera that was used to take these images. From this, we can calculate that one scanned pixel represents 0.013313 millimetres or 13.313 microns. We can use this to measure the diameter of Earth's image on the film.

On frame 5326, the diameter of Earth's image was measured to be 3,059 pixels which implies that on the film itself, it was 40.72 mm across. On the assumption that the shot was taken using an 80-mm lens (as stated in the Apollo 11 photo catalogue), we can use an equation to determine the angle that Earth subtended to the camera. This is "angle = 2arctan(dimension/2 times focal length)". This works out at 28.56°. Since we know Earth's radius to be 6,371 km, basic trigonometry gives us a distance of about 25,000 km. However, that is the distance to the limb, not to the sub-spacecraft point on Earth. For that we deduct the planet's radius which yields approximately 18,700 km.

There are quite a few sources of error in this methodology. How accurate was my measurement of the camera's gate? The piece of film I used might have expanded or contracted when compared to when it was in my camera. Did the accuracy of the lens's geometry depend on where the image was? In other words, it is possible that the lens did not have a linear geometry. How accurately could the edge of Earth be defined on the scan? It was certainly a soft transition encompassing a few pixels and some sharpening was applied to give a better edge to measure against. Note also that the technique will yield more accurate answers when the photographs were taken near to Earth. Nevertheless, as the spacecraft continues its departure from Earth, this technique will give useful results and the calculation can be applied to all 49 images of Earth that show a measurable limb.

003:57:12 Aldrin: Hay, Houston, Apollo 11. All 12 latches are locked.

At one of the links in the above posts someone said that the terminator is wrong in the photo because it is horizontal. As exclaimed here, the "terminator" is actually part of the Lunar Module.

[onebigmonkey]

I'm not entirely convinced by the AFJ's sequencing, but close examination of the entire range of photos from AS11-36-5317 to S11-36-5326 does reveal some subtle changes. Comparing the eastern edge of AS11-36-5318 and AS11-36-5326 shows that more of the Iberian peninsula is in view, which does suggest that there has been some time elapsed between the two images, more than if the entire sequence was taken in one burst.



Looking at AS11-36-5317, there's very little (if any) detectable difference on the western limb, but Greenland has moved slightly south and is viewed from a different perspective.



I dunno, it's almost as if they were on a slightly upward trajectory heading towards where the moon wiil be or something...

The AFJ has all but the final two in the sequence as immediately after docking about 15 minutes earlier, so I guess it's a matter of whether travelling at 25000mph would be enough to generate that change in view over a relatively short time.

Later on Armstrong also says this:

004:52:19 Armstrong: Well, we didn't have much time, Houston, to talk to you about our views out the window when we were preparing for LM ejection; but up to that time, we had the entire northern part of the lighted hemisphere visible including North America, the North Atlantic and Europe and Northern Africa. We could see that the weather was good all - just about everywhere. There was one cyclonic depression in Northern Canada, in the Athabaska - probably east of Athabaska area. Greenland was clear, and it appeared to be we were seeing just the icecap in Greenland. All North Atlantic was pretty good; and Europe and Northern Africa seemed to be clear. Most of the United States was clear. There was a low - looked like a front stretching from the center of the country up across north of the Great Lakes and into Newfoundland.

Which I confess is where I was inclined to base my initial timings - I'd missed that earlier comment.

I'll be going back to my page on this part of the mission tonight and do some more reworking!