4.2.7 Apollo 10 Images – Day 7: May 24th

The final colour Earthrise image in this sequence, and the first on day 7, shows AS10-35-5239 (figure 4.2.7.1) and is analysed in figure 4.2.7.2.

Figure 4.2.7.1:  AS10-35-5239 Source

In this colour sequence the elongated cloud mass arrowed in green on the previous image is now at the terminator line, and the whirl arrowed in red is the most prominent system visible. SkySafari is set at 00:45, again an orbit later than the previous image. Orbit 27 started at 00:11 on the 24th, and voice contact after AOS was at 00:52. The SkySafari graphic shows that 00:45 is not quite at the point where Earth can be seen, so the software is behaving well. The crew give no indications that they are photographing Earth at this point but they are engaged in photography duties at the time.

The appropriate image is still that of the 23rd, because the orbits of Apollo 10 are effectively keeping pace with the ESSA & NIMBUS tracks and the satellite images commenced on the 23rd have yet to complete a full day's coverage of the Earth. Because fewer of the NIMBUS tracks are available for this part of the Earth's surface, there are fewer matches, but it is presented for the sake of consistency. It is still worth looking more closely at one of the higher resolution infra-red images just to confirm that the Apollo photographs are showing high levels of detail that are matched in the satellite record - see figure 4.2.7.3.

Figure 4.2.7.2: Main image - ESSA 9 (top left upper and lower), ATS-3 (bottom left) & NIMBUS-3  IDCS (bottom right) compared with AS10-35-5239. Below this is a NIMBUS-3 HRIR mosaic and SkySafari time estimate.  To the right are 3D reconstructions using digitally recovered ESSA (top) and NIMBUS (bottom) data.

Figure 4.2.7.3: Section of NIMBUS-3 infra-red image from orbit 531 compared with the same region of AS10-35-5239

As usual it’s an almost exact match, with less than three hours between the taking of the two photographs.

We have one last still image of Earthrise to look at, this time from a black and white image, AS10-32-4808. There is an earlier image on the same magazine (AS10-32-4802), but it has the same features on it as 4808, so must have been taken during the same Earthrise event.

Figure 4.2.7.4 shows the image, and figure 4.2.7.5 the analysis.

Figure 4.2.7.5: ESSA (top left), NIMBUS-3 IDCS (bottom left) images compared with AS10-32-4808. Top right is NIMBUS-3 HRIR image. Bottom centre is a 3D reconstructions of ESSA data and SkySafari time estimate.

For this image, while it is not as high quality as the colour image we can still make out important features that help us time the photograph, namely Australia. One of the two strands of cloud across Australia extends a little beyond its coastline, so we can put the terminator somewhere off the east coast of the continent. There isn’t enough data on the NIMBUS 3D reconstruction to make it worth including there

The SkySafari time for this image is set at 06:46 on the 24th, which is the first voice contact between Houston and Apollo 10 after the start of revolution 30. Figure 4.2.7.6 shows Australia in close up.

Figure 4.2.7.6: SkySafari Apollo and ESSA views of Australia at 06:46 24/05/69

The timing is confirmed by this from the transcript:

133:13:57 CDR  Here comes the Earth. Beautiful.

And the positioning of Australia is spot on, as usual.

The NIMBUS  orbit covering Australia was commenced at 02:44 on the 24th, while ESSA’s best track for the terminator is track 8 on orbit 1085, which started at 05:24 on the 24th.

Another feature of these images is that they show a clear rotation of the Earth over that time. The weather systems visible on the images come in and out of view in a manner consistent with that rotation. The amount of movement of the globe over the timespan of these photographs matches exactly what would be expected from the Earth in that time.

We can demonstrate this with a quick look at where we would expect the terminator to move to over that time over just the 6 hours separating the 4 colour images (which as we have seen also includes one of the black and white photographs).

Figure 4.2.7.7 shows a map of the Earth with 30 degree lines of longitude marked. Marked in red are the lines we would expect the terminator to follow at 2 hours intervals. As there are two hours for each orbit, which equates to 30 degrees of Earth rotation, this makes the task slightly easier.

It should be pretty obvious from the above that not only do the weather systems on the photographs match exactly the satellite images, but the movement of the Earth in between the Apollo photographs is entirely consistent with what would be expected.

Approximately 9.5 hours after the last Earthrise image examined here, the crew began their TEI burn to launch them on the voyage home. During that voyage the crew took more photographs of the departing Moon and, thankfully for the purposes of this research, the approaching Earth.

A pre-mission document went to the trouble of providing computer generated images of the view they were likely to see at AOS after TEI. The idea was to help the crew orient itself as well as reassure them that the unfamiliar sights they were seeing out of the window were normal and to be expected. Figure 4.2.7.8 compares the predicted view with SkySafari.

Figure 4.2.7.7: Terminator lines at 30 degree intervals. The red line on the right marks the terminator line as shown on AS10-27-3889.

Figure 4.2.7.9: AS10-35-5258. Source

Figure 4.2.7.10: ESSA 9 (top left) and NIMBUS-3 IDCS (left) compared with AS10-35-5258 and SkySafari time indicator. Below this are 3D reconstructions from digitally restored ESSA (left) and NIMBUS data (centre).

The most obvious cloud mass is the complex 'S' shaped system stretching from the central Pacific to the Alaska. Another feature of note is the thin band of cloud off the California coast that stretches out into the Pacific. In the south Pacific there is a long band of cloud stretching from the Antarctic towards the tropics. Both ESSA & NIMBUS images show the 'S' system and the south Pacific arc of cloud, but loss of orbital information along the California coast means only ESSA shows detail there.

The NIMBUS-3 infra-red data (figures 4.2.7.11) again show excellent correspondence with the Apollo image, and as we get closer to Earth the details become even more impressive.

Figure 4.2.7.11: NIMBUS-3 infra-red orbits 536 and 538 . Colours used are those in figure 4.2.7.10, with a section of NIMBUS-3 orbit 536 compared with the same area on AS10-35-5258.

Orbit 536 was commenced at 06:19, less than 7 hours before the Apollo photograph was taken, which I’ve put at 14:00. The close-up shot shown in figure 4.2.7.11 above shows again that despite this time gap it is still possible to identify broad climatic patterns. In this case we can pick out the cloud that runs to the north of both the Caspian and Aral Seas before heading north to join a larger cloud mass. The western end of the Himalayas is also identifiable in both.

The next image, as will be evident from the position of the terminator, was taken 24 hours after the first of the Earthrise sequences examined above.  There are two variants of the same image here, as AS10-27-3952 (also the first image of Earth to be seen after photographs of a retreating Moon in that magazine) is very similar to AS10-35-5262 (amongst others in a short sequence of identical images). By way of variety, the one from magazine 27 will be examined here, and it is shown below in figure 4.2.7.12. The one from magazine 35 can be found here: Source. Comparison with satellite images is undertaken in figure 4.2.7.13.

Figure 4.2.7.12: AS10-27-3952. Source

Figure 4.2.7.13: ESSA 9 (left upper & lower and NIMBUS-3 IDCS (left) compared with AS10-27-3952 and SkySafari time estimate. Below this are 3D reconstructions from digitally restored ESSA (left) and NIMBUS data (centre).

At first glance the large weather system identified by the green arrow is the same as in the one shown for the 23rd (it is obviously the same cloud mass, but it now has a different shape). Features of the other systems on the satellite photographs mark the Apollo image as having been taken on the 24th, not the 23rd.

The distinctive fishtail has been lost, and it now extends a further 10 degrees of longitude over towards north Africa than on the day before. The curved cloud mass picked out by the magenta arrow runs more or less along latitude 30 degrees North on the 23rd, and the cloud bank to the east of the one identified by the blue arrow and north of the one marked by the green was not there at all. The red arrow points to a continuation of a system visible in the southern Hemisphere on the previous day in figure 4.2.6.7 (identified by a yellow arrow).

As with the previous day's image, there is much less available from NIMBUS, but there are still identifiable weather patterns. This becomes more obvious in the resolution infra-red images, as shown in figures 4.2.7.14 below.

Figure 4.2.7.14: Left - NIMBUS-3 infra-red orbits 540 & 542. Colours used match those in figure 4.2.7.12. Above - Section of NIMBUS-3 infra-red orbit 540 compared with the same area of AS10-27-3952

How many times can we say it? The Apollo and satellite record correspond just as they should - even when zooming into small areas, like the one off North-Africa shown in figure 4.2.7.14 (above right).

As far as timings go, SkySafari suggests a time of 18:45 on the 24th, which would have been shortly before the start of another of their TV transmissions. ESSA's orbit for the Atlantic on this date is number 1091 (track 2), which started at 16:08. NIMBUS' equivalent (of the ones available) orbit is 540, which started at 13:47.

A couple of hours after these photographs were taken the crew made yet another of their regular TV broadcasts, and again Earth was featured as part of it. The broadcast took place between 20:12 and 20:23 on the 24th, and a still from it is examined in figure 4.2.7.15.

Figure 4.2.7.15: Still from TV broadcast compared with ESSA image dated 24/05/69. Below this are 3D reconstructions from digitally restored ESSA (left) and NIMBUS data (centre) and SkySafari time estimate.

The long arc of cloud in the Atlantic (blue arrow) is very easy to make out on the TV image, and once you have that located it’s a pretty straightforward job to pinpoint the west coast of South America and the stream of cloud just off it (green arrow).

As ever the crew give us a description:

147:23:08 Young: Houston, this is Apollo 10, 184,000 miles [34,750 km] out. This is the Earth, half-Earth. It's about - the Moon right now. We have practically a full Moon. The Earth, as you can see it right now, is - The terminator is going right across the middle or the Atlantic. You see that big circular weather belt that goes up across the United - up across the east coast of the United States, covers up Florida, and it appears that some sort or point is in the Gulf of Mexico between Florida and Texas. It's difficult to make out any land masses and I doubt that you could see any, but with the monocular, I can see Cuba, Haiti, and the Indies, and most of South America which is cloud cover. The central United States appears to be open, as well as the western United States, as far as I can see.

147:33:52 Young: Roger. There's a great big - a great big swirl right over the - light over the point south of Florida, goes up through the eastern states. That was clearly visible on the - at least through the - in the monitor up here. So, you'll probably be able to see it down there, and, also, another swirl; it looked like it was up north, somewhere, possibly as far north as the Canadian border there, coming down to sort of join them together. Couple of very interesting weather pattern.

147:34:25 McCandless: Roger. We were able to see the cloud patterns, very clearly here, on the black and white monitor; and I understand, from people who were watching the smaller color monitors, that the color was excellent. Over.

147:34:40 Young: Roger. Well, or course. I didn't expect you were seeing any more than we were on our monitor; and you couldn't - couldn't recognize any land masses to speak of or any - possibly you could see South America, down there in the south, under that big bank of cloud cover, because that's the only thing that I could really pick out with my naked eye.

And as ever the descriptions are uncannily accurate. We have an even clearer view taken a short while later on magazine W (figure 4.2.7.16).

Figure 4.2.7.16: Apollo 10 video still compared with ESSA satellite images from 24/05/12 and SkySafari time estimate. Below this are 3D reconstructions from digitally restored ESSA (left) and NIMBUS data (centre).

While they two scenes look very similar, close examination shows that the Atlantic cloud front is much nearer the terminator and an additional weather system is now visible on the western limb.

There are no ATS images available for this date, and the Nimbus record is so patchy it was not worth including for this comparison. ESSA’s best track for the terminator line is track 3 (orbit 1082) was commenced at 18:02 on the 24th. SkySafari’s estimate of the time at 21:45 is mainly based on the visibility of most of Chile on the west coast of South America. There’s no record of any filming at this time in the transcript, but it’s likely that John Young was filming as Cernan and Stafford were giving a lengthy debrief to Houston at this time.

That’s it for day 7. Click the link for Earth images taken on day 8.

The pre-mission time is given as 137:29:32, which compares witth the actual time recorded as 137:45:47, which is pretty accurate. The view is obviously correct, which is to be expected given that the view is easily predictable. Did the crew enjoy it?

137:45:34 Young (onboard): Do you see the world?

137:45:35 Stafford (onboard): …no

Ah well!

One of the first images of the Earth on the way home (and the first of Earth after those of a full disk and obviously shrinking moon, is AS10-35-5258 (figure 4.2.7.9).

Figure 4.2.7.8: Comparison of pre-mission document and SkySafari views of Earth at AOS after TEI.