4.7.7 - Apollo 15 Day 7 - On the ground

Day 7’s Earth image consists of one short sequence of live broadcast during EVA-2, listed at the ALSJ as being the first live TV broadcast of Earth from the moon.

The camera pans up as equipment is being transferred to the LM, and is then forcibly panned back down again as the camera gets stuck pointing at the high upward angle. The timing of the footage works out at 18:40 GMT on August 1st 1971, so we can get a good idea of where the Earth would be in the sky at that point.

As there is a substantial gap between when we see the Earth in the pan upwards and the last recognisable landmark of the LM, it’s difficult to work out exactly how far above the LM the Earth is in the footage. It’s easier to use the forced return to horizontal of the camera as this is much quicker and therefore occupies fewer frames of footage. If we assume a constant speed we can use the lens flares in the frame as markers and try and get an idea of where the Earth is in the lunar sky.

Figure 4.7.7.1 shows a Stellarium view of Earth at the time of the broadcast compared with a compilation of screenshots from the footage. The lunar background is from Apollo 11, and is there purely to provide a horizon.

Figure 4.7.7.1: Stellarium view from the Apollo 15 landing site of Earth during the end of the EVA-2 TV broadcast compared with a screenshot compilation from the LM to Earth. Source.

It’s clear from the Stellarium shot that Earth is well above the horizon (the crew consistently complained of the difficulty of angling the LRV antenna towards Earth because of both the angle and the sun being in view). Earth is at angle of 204 degrees from lunar north. Examination of the Earth in the screenshot compilation shows it to be above St George’s crater. Figure 4.7.7.2 shows the angle of the crater from the LM.

Figure 4.7.7.3: Angle of St George’s crater as calculated from the Apollo 15 LM

Pretty much bang on. It’s also worth pointing out that the angle of the lens flares is completely consistent with where the sun is relative to the camera and Earth.

We can also see (figure 4.7.7.4) that the Earth’s phase is completely consistent with what should be visible.

Figure 4.7.7.4: Stellarium view of Earth compared with TV screenshot

While it would not be reasonable to suggest we can make out any detail in the image of Earth (of which I have adjusted the contrast) we can certainly see that the phase is consistent with what we should be seeing.