NASA Camera Shows Moon Crossing Face of Earth for 2nd Time in a Year | Hacker News Reader

NASA Camera Shows Moon Crossing Face of Earth for 2nd Time in a Year

nasa.gov

199 pointsdnetesn65 comments

Awesome shots! Because of the particular angles & distances, it looks like the moon is almost grinding against us! Of course, that's just an optical illusion; the actual distance & proportions are more like https://en.wikipedia.org/wiki/Lunar_distance_(astronomy)#/me...

The moon is about 1/4 as far away from earth as the camera is. The camera always sees the sunny side of the earth - neat trick! http://epic.gsfc.nasa.gov/

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.

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.

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 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...

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?

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

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.

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)

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.

Now it's official: no evil cooperation operates on the backside of the moon.

Not so fast, what's that dark patch in the upper left?

TMA-1, duh.

Not on the surface, obviously. That would be silly.

Although how awesome would that have been.

"Ok, the photos are coming through now. Which, lol, should provide conclusive proof that no one is operating on the dark side of the.... what the hell is that?"

I'm sure Amazon are already planning a warehouse there..

Don't be silly! Evil corporations don't have farside moon bases!

No, this proves that there aren't any space nazis on the far side of the moon.

FALSE: Everyone knows that the Nazi's aren't on the moon that was just a diversion, they are in the hollow earth...

Just a quick dumb question : where are the satellites and the stars ?

Too dim to show up in an exposure calibrated for a nearby sunlit Earth.

Same with the Apollo photographs taken on the Moon – the surface is just too bright.

"Since Earth is extremely bright in the darkness of space, EPIC has to take very short exposure images (20-100 milliseconds). The much fainter stars are not visible in the background as a result of the short exposure times." - http://www.nesdis.noaa.gov/DSCOVR/

Thanks ! It makes sense. :-)

There's another cool one here showing a solar eclipse.

http://earthobservatory.nasa.gov/IOTD/view.php?id=87675&eocn...

It's called "mooning", not "photobombing"

The history of the DSCOVR satellite is pretty interesting. Was pushed for by Al Gore in the 90's -- unofficially known at the time as GoreSat -- but was ultimately killed by the Bush administration. Obama's administration resurrected the project, and now we have an amazing view of earth for science, discovery, and some pretty neat pictures.

https://en.m.wikipedia.org/wiki/Deep_Space_Climate_Observato...

A few days ago, in a moment of 6-degrees of youtube, I came across a flat earth video. Out of curisoity to see what their beef was, I watched one. It was interesting. One of the claims was that all of the earth images we have are not actual photos or pictures per se, but rather, artists renditions (I think they used a different term which I don't recall at the moment). Apparently, this point was admitted to by NASA too. And they had pictures of earth from space (taken and distributed by NASA) over the years where continent sizes change drastically on the same circle. One of them even had "sex" spelled in the clouds.

Watching this, it too looks like an artist rendition. Notice how the moon moves in a straight line. And while the earth rotates around, the moon doesn't. That is fine as we see only the same side/face of the moon but remember: this is taken from far far away so, at that distance and angle, you should be able to pick up a change in the moon's rotation as well. Here, we don't.

Interesting indeed.

I know the moon has a low albedo (reflectivity) but it's easy to forget until you see it compared to the earth like this.

Are there full size static images somewhere? I want to look at the photos but the gif isn't doing it for me

http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11971

This link is actually the first time this happened last August, not the second event referred to in the subject article.

This page has static images of the current event: http://epic.gsfc.nasa.gov/galleries/lunar_transit_2016/

I've never given it much thought but the first thing that hit me is that the moon really is just a big 'ol rock up in the sky. These images have changed the way I view the moon. Pretty neat.

Looks like the NASA satellite got mooned

aaghhhhh

Really, -4? Man, HN sucks

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Yeeeeeessss thank you hahah the collective groan is deafening!

Edit: man some of y'all need a sense of humor.

Right? Stiffest forum on the internet right here

If I understand correctly, satellite is directly between sun and earth (at lagrange point L1?), and somewhere at the time of the shooting there was an solar eclipse seen somewhere in Australia

Edit: nevermind, "The satellite is orbiting the Sun-Earth L1 point in a six-month period, with a spacecraft-Earth-Sun angle varying from 4 to 15 degrees", so it's not directly between.

Yes, it's at the L1 point: https://upload.wikimedia.org/wikipedia/commons/a/a5/Lagrange...

No idea about the eclipse, though. There is none listed in NASA's eclipse portal for July: http://eclipse.gsfc.nasa.gov/OH/OH2016.html

Objects at Lagrange points L1 (between), L2 (small-body side), and L3 (large-body side), either have to continually spend propellant to keep station or use a Lissajous halo orbit around the point.

In space, the choice to use more fuel or less fuel requires little consideration. So this satellite essentially scribes an elliptical ring around the sun as viewed from Earth. If the Moon passed between the satellite and the Earth, the Moon would appear from Earth to be 4-15 degrees away from the Sun, which would just be an ordinary new moon, not an eclipsing new moon.

Slightly related, here is an L1 satellite's view of a solar eclipse that I stitched together from Japan's Himawari-8: http://earth.apawl.com/eclipse/

What is that black triangle in the lower right of the image? And why is it moving?

EDIT: Okay, never mind, I just realized these images were taken over the course of several hours, so the triangle must be a movie-composition artifact, caused by the camera not being fixed.

Yeah, well - I think the moon is pretty good natured after astronauts walked on its face.

Proof: https://m.youtube.com/watch?v=eM1hv9ileaA

wow, I didn't realize we had satellites up that high.

It's actually orbiting the Earth and the Sun at the same angular rate. It will make one orbit around the Earth per year. Normally, things that have smaller orbits around the Sun move faster than the Earth. But if you start the satellite's orbit near the Earth, the Earth's gravity will pull it back and slow it down a bit. If you're very careful, you can get them to balance out so the satellite orbits the Sun in one year instead of going faster.

How far away from earth is this satellite? Further away from the moon?

Yes. In the article, it states the satelite is 1 million miles from Earth. That's a bit more than 4 times the distance Earth-moon.

Original source at NASA (which, as usual, phys.org does not link to, they even ripped the short movie from youtube)

http://www.nasa.gov/feature/goddard/2016/nasa-camera-shows-m...

yeah, phys.org as a source always make me slightly suspicious, clocking in at about the level of a university press release in terms of trustworthyness.

NASA's own press release at least specifies how unusual this event is, and the answer is "a bit less unusual than new years"

Thanks, we updated the link from http://phys.org/news/2016-07-nasa-camera-moon-photobombing-e... to this.

That's no moon!

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