4.5.5 - Day 5: Homeward Bound

Technically the next image in the sequence is AS13-61-8826, which is preceded by a series of lunar far side photographs, and therefore must have been taken after they successfully completed their TEI slingshot burn at 02:45. It’s shown in figure, but the analysis has been saved for the much better quality version of the next in the series, AS13-60-8716 (figure, Source). The next sequence of images from Magazine 61 (eg AS13-61-8842) have views that mach the magazine 60 image, but aren’t as clear.

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Figure AS13-61-6826. Source given in text, with SkySafari terminator depiction

The time for this photograph has been fixed largely by referring to the analysis in the next photograph, where there is a clear view of Australia, but we can also look at the satellite image to show that the large swirl of cloud in the North Pacific, which nestles snugly in the Gulf of Alaska. IT even seems to get a reference in the transcripts, where at about 04:55 we have this:

081:35:32 Haise: Man, that's a wicked low pressure down there.

The analysis in figure, and makes this clearer.

Figure AS13-60-8716. Source given in text

Figure AS13-60-8716 compared with ESSA satellite (top left) and NIMBUS IR view (above). Above right is another NIMBUS IR image compared with a smaller section of the image (right). Below the main image are a SkySafari depiction of time at terminator and 3D reconstructions using ESSA (centre) and NIMBUS (right) images.

The dominant weather system (blue arrow and shown in 4.5.15b) on the map is a development of the one identified by the blue arrow in figure 4.5.6, and its centre is still located roughly over Alaska & Kamchatka. Close inspection of the south-west horizon shows that Australia is just visible, and this helps to pinpoint the time as being roughly 05:00 on the 15th.  As far as ESSA's timings concerned, the image used is dated the 14th, but the most relevant orbital pass for this part of the globe is orbit 5155 (track 6), which was commenced at 01:04 on the 15th, again just a few hours before the Apollo image was taken.

It’s worth pointing out that the 3D reconstructions show more of Australia than is actually visible. It’s a fiddly process getting those views right, but the position of the terminator is correct.

The next image in the sequence is AS13-61-8864 (source: AIA). This photograph occurs at the end of a sequence of images showing an ever decreasing Moon. Towards the end of the magazine, there are a couple of photographs of the adapted lithium hydroxide canisters used to scrub the cabin air clean of surplus carbon dioxide. The procedure to adapt these canisters began at around 90 hours in, or around 13:30 on the 15th, so the images of the Earth must have been taken before then. We also have confirmation that they have been taking Earth images:

082:57:30 Haise: Okay. Jack's got the one with the 250-millimeters lens on it. That's the standard EL. And I have a surface camera out that I've been shooting hundreds of Earth/Moon pictures with, camera 1.

That transcript time equates to around 06:15

Figure shows the original Apollo image, and figure has the same image compared with satellite photographs.

Figure AS13-61-8864 – source given in text

Figure AS13-61-8864 compared with ESSA (top left), 3D reconstructions of digitally restored satellite ESSA (centre middle) and NIMBUS (centre right), NIMBUS satellite IR data (left) and SkySafari estimate of time at terminator (left). Cyan, green and red arrows as figure

What the image shows is that weather patterns that were towards the west of the globe have moved much closer towards the terminator, and systems identified in figure 4.5.15 can also be identified in figure 4.5.17. Australia's position on the terminator allows a relatively precise estimate of the time the image was taken: 08:15. As the satellite photograph is dated the 14th this gives the appropriate orbital pass as number 5158 (track 9), commenced at 07:01 on the 15th. A few hours after the Australias enter darkness, ESSA starts a new collection of orbits that will have the next day's date on them.

Two images later in this magazine we have a similar view in AS13-61-8867, again with the Earth framed by the LM quad thrusters. As with other Apollo images that are ostensibly identical, close examination reveals that there are differences along the terminator that show that it was taken a short while after AS13-61-8864, rather than at the same time.

AS13-61-8867 is shown in figure below together with a zoomed and cropped Earth.

Figure AS13-61-8887 with SkySafari time estimate

There isn’t much point in repeating the analysis, but close examination of the cloud systems along the terminator show that there has been definite rotation. The clouds over western Australia identified by the yellow arrow in figure, for example, are now almost on the terminator, as is the system picked out by the green arrow.

There are no firm hints in the transcript specifically about these last two photographs, but capcom is informed regularly at around this time of the angle at which Earth appears on the LPD (Landing Point Designator - marks on the LM window designed to aid distance gauging),as they make sure they’re still pointing at home.

The next Apollo image to be looked at is AS13-60-8720 (Source: AIA). There are no real clues in the remainder of this magazine as to when it might have been taken, other than it is after images previously examined from this film, so we are reliant in what we can see in it (figure Figures show the satellite images as a comparison.

Figure AS13-60-8720. Source given in text.

Figure S13-60-8720 compared with ESSA (top left), NIMBUS (centre right) and ATS (centre left) satellite images, with SkySafari estimate of time at terminator centre left. 3D reconstructions of digitally restored ESSA (centr emiddle) and NIMBUS IR (centre right) satellite data. Zoomed and cropped and compared with NIMBUS IR image are bottom row.

It doesn't take much zooming in on this image to see that the terminator line crosses north Africa somewhere along the coast of Tunisia/Algeria, which gives a time of the photograph as around 18:00.The main weather system visible over the Atlantic is the same one observed in figure, but it has changed in the couple of days since it was first photographed, separating itself from the other clouds in the mid-Atlantic and rotating so that the south-western tip is closer to Africa than it was previously. The close-up NIMBUS image nicely shows the swirl of cloud in the Atlantic.

The movement of the Earth has also brought the ATS satellite back into play when confirming the timing of the Apollo image. ATS' image is time stamped at 15:59 on the 15th. ESSA's most representative orbit is pass 5161 (track 12), which commenced at 13:06 – not long before the ATS image, and within a few hours of the Apollo photograph.

The next picture to be analysed in full is the final image in magazine 60: AS13-60-8726. Between the preceding image and this one there are only a few pictures of a now very small Moon. Before doing that, we need to look at a sequence of images contained in magazine 62 again has a very similar image in AS13-62-8947 and AS13-62-8954, but there are few clues there as to when precisely this image could have been taken (other than it being after the lithium hydroxide conversion), so we are reliant again on the position of the terminator and satellite analyses. Figure shows these.

a) AS13-62-8947

b) AS13-62-8954

Figure AS13-62-8947 and AS13-62-8954 with SkySafari time estimates. Left is an ESSA satellite image from April 14th showing the USA, as published in the Sarasota Herald Tribune on April 15th.

The key to timing these two images is the position of the large weather system across the centre of the USA, and the smaller system over New England shown in the ESSA view. The central system is very close to the western limb. There’s enough of the southern Pacific off the coast of Chile to also allow a reasonable time estimate. There is obvious movement between the two, and I’d suggest no more than 30 minutes have elapsed between them.

It becomes much easier to tell the time when we look at the more detailed view shown in AS13-60-8726 (figure, and the analysis in figure

Figure AS13-60-8726

Figure AS13-60-8276 compared with ESSA (top left), ATS (second row left) and NIMBUS IR (second rowright) satellite images, thir d row: 3D reconstructions using digitally restored ESSA (centre) and NIMBUS IR (right) satellite data. SkySafari estimate of time at terminator above. Green arrow as in figure Bottom row zoomed and cropped part to compare with NIMBUS IR image over Canada.

At the risk of pointing out the obvious (again), there is a degree of overlap between this image and the previous one. The 'speech bubble' cloud identified by the green arrow in figure 4.5.22 has now been split by the terminator line, and the north American mainland can be made out to the west of it. The more detailed NIMBUS IR image shows excellent correspondence with the Apollo photo over Canada.

Using this terminator line SkySafari times this image as roughly 22:30. The ATS image is till the 15th, and the ESSA image is also dated that day. The ESSA pass covering the Atlantic seaboard is track 2, which translates to orbit number 5163, commenced at 16:07. By this time in the journey the CSM and its attendant LM had just passed into the Earth's gravitational sphere of influence and were beginning to accelerate. The crew were also preparing for a mid-course correction burn.

There’s one more image in this sequence of Earth photos, all timed around the crucial correction burn that ensures their safe arrival back home, and that can be seen in figure

Figure AS13-62-8960 and SkySafari time estimate

The storm over New England has now completely disappeared into darkness, as has South America.

Having  survived another 24 hours, we move on to day 6 of the mission - click the link below.