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    Re: Sunrise on the Moon?
    From: Frank Reed
    Date: 2021 Feb 21, 08:06 -0800

    Note: first three paragraphs of this post are off-topic. There's some more-or-less on-topic astronomy after that...

    I'm so glad you brought this up! Did you watch season one of "For All Mankind" yet? I enjoyed it enough that I re-watched almost all of it last week before season two began (s2's first episode with the sunrise that Bob is describing was released two days ago while s1 originally aired in late 2019). 

    Alternate histories are an amusing form of science fiction, albeit slightly sleazy (and therefore in the guilty pleasure category). In this case the setup for the whole series is that the US and NASA lose the Moon race. In a surprise success, right at the beginning of the first episode of the first season, the Soviets manage to launch their N1 rocket and their lunar spacecraft and Alexei Leonov becomes the first man to land on the Moon. Apollo 11, a few weeks later, is no longer a triumph but instead a desperate attempt to catch up and "save face". Within a few months the Soviets also land a woman on the Moon.

    The alt history premise here is that the continuing competition between the superpowers is actually "good" for space flight (if you're a "space cadet" who thinks that all human space flight is essential and "super cool"). So the Apollo missions to the Moon continue for many years, and a base, called Jamestown, is built near Shackleton Crater at the Moon's south pole. Other history also changes in trivial ways and in major ways. An example of a trivial change with major consequences: because the landing of Apollo 11 is no long a celebration and becomes a desperate attempt to recover from the shock of the Soviet surprise landing, there is no party the night before Apollo 11's landing on Martha's Vineyard so there is no Chappaquidick and Ted Kennedy's political career is not damaged. He becomes President of the US, the second Kennedy, in the early 1970s. It's worth watching if you like this type of historical science fiction, and as I say, it certainly has a "guilty pleasure" aspect. If you want a single episode of season one for flavor, try "Hi Bob" (the reference in the title is very clever) and if you want some good space drama with lots of good geeky spacecraft detail, try the last two episodes of season one.

    By and large the science in "For All Mankind" is good and not far from reality. The creators of the series are mostly veterans from other great recent science fiction work, and they care about "hard sci-fi" as well as the details of space flight. The sunrise in this first episode of season two was an exception. I feel that it simply sounded too good in "story-boarding" as the episode was planned, and they set aside the science problems for artistic license. The show uses nostalgic music to good effect, and this was an interesting opportunity to bring in a little Bob Marley, which I thought worked well. 

    A few problems with the depiction of sunrise:

    • As Bob has noted, given the low inclination and the location near the south pole, this would be a gradual thing lasting weeks with no sudden "sunrise" moment.
    • The Sun would not rise vertically as it would near the lunar equator. Near a lunar pole, it would travel around the horizon once a month, peaking out occasionally through valleys and dips in the terrain.
    • Even at the Moon's equator, a lunar sunrise would be nearly 30 times slower than a terrestrial sunrise --not very dramatic and you wouldn't stand around watching.
    • The corona of the Sun would precede the disk and offer the "beautiful" phenomenon that they were aiming for in the episode.
    • Observers at different altitudes above the lunar surface would see the Sun at different times. Dip on a different scale.
    • The sunlight would be blinding (in the literal sense), and this is the biggest problem (more below).
    • Moments of "deep" night as portrayed in the episode would be rare since the two-degree-wide Earth would nearly always be visible.

    Here on Earth, during a total solar eclipse, the Moon blocks the Sun's disk completely. In the moments just before and after totality, small slivers and points of the brilliant disk are still visible. Their total luminosity is insufficient to generate our "blink" reflex to convince observers to look away, but those little slivers of the Sun's disk have exactly the same brightness per unit area as the normal Sun so they can burn and permanently damage the retina. That's the major risk during a total solar eclipse: we don't look away by natural reflex when 99.9% of the Sun is obscured. It's beautiful and difficult to look away. Note that we don't face this problem at sunrise/sunset on the Earth. Even though these events begin/end with a small sliver of the Sun appearing above the horizon, the Sun is radically reduced in brightness by absorption in the atmosphere.

    On the Moon, a sunrise would be comparable to a solar eclipse. In fact, it is a solar eclipse: the body of the Moon is blocking the Sun. Portions of the corona would appear above the horizon before sunrise, followed by the slow emergence of the solar disk (talking now about a solar sunrise somewhere else on the Moon, for example near the equator). As on Earth, those first small slivers of the Sun appearing above the horizon would be dangerous. They would be dazzling, but they would not generate the usual reflex to look away. And the Sun's light at sunrise/sunset on the Moon is not diminished in any way. It is every bit as bright as the Sun at the zenith on the Moon, which is also about 30% brighter than the Sun at the zenith here on Earth. Watching a sunrise or sunset could easily cause permanent damage to an astronaut's eyes, whether in this history or an alternate history!

    I did not scream at the screen during this sunrise scene. I understand that they couldn't resist the artistic impact of the scene, and it advanced the plot rather than damaging it. But I did grumble at the screen (more than once!). There were details of a solar storm in this episode that were also significantly modified for artistic effect, but that bothered me less since an invisible storm is problematic for video.

    Frank Reed

    The image below shows a "bunch" of astronauts watching the spectacular, dramatic sunrise (well, no, and since they don't have their visors down, they all now have severe retina damage).

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