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Comment by danso | Hacker News Reader

I hope people don't flag this because of its admittedly millennial-sounding headline...I'm not a huge astronomy geek but was surprised at this particular juxtaposition of two familiar entities. It almost looked Photoshopped. I was also surprised that this kind of visual arrangement is unusual enough to warrant an article, but that's because I'm clueless to where our satellites are usually positioned in relation to the Earth and moon.

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I believe the photo shopped look is due to the visual artifacts caused by the delay between light frequency shots mentioned in the article

Yep, three colors, 30 seconds apart.

Each exposure is 40 ms. The EPIC camera images at 317, 325, 340, 388, 443, 552, 680, 688, 764, and 779 nm. It transmits one photo of each spectral slice every hour.

I would guess that channels used for a composite color photo for human-eye viewing would be 443nm (blue), 552nm (green), and 688nm (red), but 680nm is also a visible color (red). The NASA article also implies that one red or the other is imaged first, and green is last, so they are not taken in ascending or descending wavelength order. It is also ambiguous as to whether each spectral slice is 30s apart, or whether it is 30s total timespan between the red and green slices.

Basically the only way to get a view like this is to be in a lissajous orbit at the Earth-Sun L1 point and happen to get a lucky alignment between the satellite, earth, and Moon sometime near a full moon.

If the moon is on the sunny side of the earth, it's going to be a new moon (as viewed from Earth), not a full moon.

Of course you're right.

Earth sees the other side, so it's a new moon from earth and a full Moon from the satiate. However, due to location closer to the sun (L1) the satellite always sees the sunny side of the Moon.

What I can't understand in this animation is how come the clouds does not change during the 4 hours span?

Just a guess but I suspect it's because the clouds are in fact moving, just not quickly enough to be noticeable from that distance.

I agree. I'm not a crazy conspiracy theorist, but this looks photoshopped. The clouds are not moving and the moon is not rotating at all :

http://imgur.com/prywsJq

The Moon won't appear to rotate because this is only covering a very short arc of its total orbit. Despite appearances here, the Moon is a long way away. The Earth's diameter is about 13 mega-metres, but the Moon is about 400 mega-metres away. So here the Moon is moving through a tiny proportion of its orbit.

So just as when you look at a very small section of a circle it appears more-or-less to be a straight line, so when the Moon moves through a tiny portion of its orbit it doesn't appear to rotate.

The clouds are moving. But you have to remember HUGE cloud formations move fairly slowly. Consider this shot is only about four hours. If you don't believe me, look at the clouds about 1/3 of the way down, over Mongolia I believe, they finish up near the center... As they move across the screen they get thinner. As far as the moon rotating, it takes about 28 days for it to rotate, this was 4 hours. So it will rotate about 2 degrees?

The clouds absolutely are moving.

Yes maybe and the distance between the Earth and the Moon could explain why we don't see the Moon rotation :

https://en.wikipedia.org/wiki/Lunar_distance_(astronomy)#/me...

Clouds don't move very much on a planetary scale over a single day: http://himawari8-dl.nict.go.jp/himawari8/movie/720/coastline...

The Earth's rotation in the original gif makes it more difficult to see the cloud movement, but it's certainly present.

Surface points on the equator rotate at about 1000 mph, while, relative to the surface, clouds move at a few percent of that; at a global scale, the clouds aren't going to move that much over the course of three and a half hours.

The moon is tidally locked to the earth and thus only rotates at about one revolution per month (about 27.3 days relative to the stars and about 29.5 days relative to the sun and to the DSCOVR satellite at the Earth-Sun L1 point which took these pictures);

Again, rotation that slow isn't going to be obvious in a time lapse covering only three and a half hours (if I'm doing the math correctly I'd expect under 2 degrees of rotation during the period covered by this timelapse)

How come the moon does not rotate?

The moon is tidally locked to the Earth. It does rotate, in the same amount of time that it orbits the Earth.

https://en.wikipedia.org/wiki/Tidal_locking

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