From a million miles away, NASA camera shows moon crossing face of Earth | Hacker News Reader

From a million miles away, NASA camera shows moon crossing face of Earth

nasa.gov

437 pointsdnetesn153 comments

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Here's what one million miles looks like side on...(whipped up in Photoshop)

Best viewed at 100%. The image is more or less to scale. Scroll a million miles to the right to find moon and camera.

(don't worry it's only a 300K jpeg)

http://ozimg.s3.amazonaws.com/earth-moon-from-million-miles....

Nice. Also THEMIS took a shot in 2001 as it was headed to Mars that captured this distance.

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00559

Dang.. it never occurred to me how big the moon is.

Looking at this picture, it's hard for me to comprehend why the moon would orbit the earth and not fall into the sun.

If you take the earth away the moon would still be orbiting the sun.

So sure, the moon is far from the earth, but that just means it takes ~28 days to orbit the earth.

PS: The moons orbit is actually 29.5 or 27.3 days depending on how you count it.

The gravitational influence of the Sun on the Moon is greater than the gravitational influence of the Earth. In a very real way, the moon is orbiting the Sun.

However, the orbit it flies around the Earth only very slightly modifies it's orbit around the Sun. The lunar orbital speed around the earth is ~1km/s, while the orbital speed around the sun is ~30km/s. That is, it never loops backwards on it's path around the sun, it's orbital velocity is at most only reduced by about 3%.

Picture from wikipedia: https://en.wikipedia.org/wiki/File:Moon_trajectory1.svg

Nice illustration in wikipedia. I first learned about this feature of the moon's orbit from one of Isaac Asimov's science essays. In many ways, the Earth and Moon are like a double planet, though not so much as Pluto and Charon.

Is this also true of Jupiter's moons?

No. Europa and all the moons closer to Jupiter than it do in fact occasionally travel backwards in relation to their orbit around the Sun. This is also true of Dione and all the moons of Saturn lower than it, all the inner moons of Uranus, and all the regular moons of Neptune.

The gas giants are much more massive than earth, while also being much further away, and many of their moons orbit closer to them. This all combined makes some of their moons pulled more strongly by them than they are pulled by the sun.

Dude this is amazing. I did not know this. TIL.

TunaFish and Retric gave great explanations, but I want to add a quick conceptual point: the moon (and the Earth) is falling into the sun. Constantly. It's just that the moon (and the Earth, and the other planets) have so much velocity tangential to the direction of the sun that instead of falling into the sun, they fall around the sun. That's what an orbit is.

The moon is falling into the sun, just like the earth.

Falling but missing the ground.

RIP D.A.

Really nice! Are the stars from an existing picture, or did you generate them somehow?

Google images copy and paste the same image a few times, then rotate/flip each instance to avoid the tile effect.

Earth and Moon from NASA.

BTW, 80 pixels in the image is approx 7917 miles (diameter of Earth). Width of image is 10,080 pixels, pretty much 1 million miles. Moon is 238,855 miles from Earth or about 2400 pixels in.

Very cool, thanks for the info.

It is really cool how the NASA gives us a better understanding of the universe and our place in it by publishing all these nice pictures.

However, I would like to have one easy accessible source for all the nice pictures that is daily updated and could be synchronized to a local school server e.g. with rsync. Is there one "ḧere-are-all-the-pics"-ftp server anywhere? It is quite time consuming to browse the hundreds of NASA sites and download pictures manually - instead I would like to spend that time browsing a local incoming folder to select the best pictures.

Would be a great service to the world to have easier access to these pictures.

Not quite what you requested, but NASA's Astronomy Picture of the Day[1] is very cool. It has an archive dating back to the 1995!

[1] - http://apod.nasa.gov/apod/

Thanks for sharing. I think I will spend next several hours digging through.

Completely unnecessary side note: It's run by one of my old professors[1]! The whole physics department at Michigan Tech is a cool little diamond in the middle of the Upper Peninsula rough.

1: http://www.phy.mtu.edu/faculty/Nemiroff.html

(Totally off-topic, but that's not a very apt usage of "diamond in the rough": https://en.wiktionary.org/wiki/diamond_in_the_rough )

The UP is sparsely populated and not nationally known for high-tech industries or science, but rather wilderness, logging, mining, hunting, and general backwoods-ish-ness.

Houghton is the exception; hidden under that rough-and-wild exterior are some rather outstanding minds, particularly in physics and atmospheric sciences.

I think it works, but to each their own :)

That does sound like a great thing to have. Maybe this is something Code for America http://www.codeforamerica.org/about/ can do?

It's not quite what you're asking for (though I haven't looked around for alternate interfaces), but the NASA Photojournal site is really nice: http://photojournal.jpl.nasa.gov/index.html

The image, without the Javascript:

http://www.nasa.gov/sites/default/files/thumbnails/image/dsc...

Interesting note (from NASA?) to visitors embedded in the page:

    <script>  (function($) {
    $.reject({
    display: ["msie", "firefox", "safari", "opera", "chrome",   "gcf"],
      reject: { 
          msie5: true, msie6: true, msie7: true, msie8: true, msie9: true, firefox2: true, firefox3: true, firefox4: true, firefox5: true, firefox6: true, firefox7: true, firefox8: true, firefox9: true, safari1: true, safari2: true, safari3: true, safari4: true, opera1: true, opera2: true, opera3: true, opera4: true, opera5: true, opera6: true, opera7: true, opera8: true, opera9: true
      },
      imagePath: '/sites/all/modules/contributed/jreject/jReject/images/',
      enable: true, header: "Did you know that your Internet Browser is out of date?", paragraph1: "To ensure that all features of NASA.gov work effectively, please upgrade to the latest version of one of these web browsers. <br /><br />For Internet Explorer users: The site will only be fully functional on version 11 with compatibility mode turned off. If you're using version 11 and you're seeing this message, compatibility mode is turned on in your browser. If you need compatibility mode turned on to use other sites or applications, you'll need to use another browser to see the full NASA site.", paragraph2: "Just click on the icons to get to the download page:", closeMessage: "By closing this window you acknowledge that your experience on this website may be degraded.", closeLink: "Close This Window", closeURL: "#", close: true, closeESC: true, closeCookie: true, overlayBgColor: "#000", overlayOpacity: 0.8, fadeInTime: "fast", fadeOutTime: "fast"
    });
  })(jQuery);</script>

Fyi this is almost verbatim from what I've seen on several other sites. I'm assuming they just grabbed a browser identifying script from somewhere.

That popup is incredibly annoying on mobile and the close link doesn't work in the Android browser.

I'm a NASA engineer, and I think one of the problems that we recognize is just how much fragmentation there is between org units, projects, programs, and centers (each of which can be surprisingly autonomous). A single mission may have several "official" websites, depending on how the work is distributed across the agency.

Your wish for a single-accessible source for images would be great. For that to happen, we would need to have someone dedicated to curating it from so many possible sources, under mandate from HQ.

For general raw data (not necessarily images), an effort like that does exist, though it isn't yet supported by every program: https://data.nasa.gov/

I agree with the bunker mentality of the NASA centers. That said, the PDS (https://pds.nasa.gov/) is the closest thing to a central source for planetary data and imagery. And they run the photo journal (http://photojournal.jpl.nasa.gov/index.html)

I agree. Presentation is everything and images from the Voyager, Cassini, Hubble, the Mars landers, New Horizons, have done so much to inspire writers, artists, and has gotten kids interested in Science.

A repository of images would be amazing and provide a terrific return on investment intellectually, artistically, and even monetarily if a small fee was charged to maintain it.

Those pictures have already been paid for by taxes. We should not have to pay for them again.

you wouldn't be paying for the images, you'd be paying to have somebody do the grunt work of organizing them, presenting them, etc

I want to emphasize that organizing these images would be a non-trivial amount of work. More worthwhile than bombing a bunch of sand people somewhere, certainly, but still non-trivial.

I think the same could be said for all public domain images published by the government. There must be a tremendous wealth of high quality photos that are hidden away on various agency websites. I've been thinking about creating an aggregation service for this similar to unsplash.com.

What would be really cool too, is something like http://himawari8.nict.go.jp/ with the (more-or-less) real-time pictures from DSCOVR.

Maybe as interesting is where this satellite is: The Lagrange L1 point. The 5 Lagrange points in essence allow orbiting bodies to break Kepler's laws. A satellite a million miles closer to the Sun shouldn't have the same orbital period as the Earth... but it does.

That's because Kepler only assumes 1-body interaction! With 2-body, or N-body, then you get lagrange points. It doesn't "break" Kepler's law, it is just that Kepler law doesn't apply in 3-body interactions.

This might just be semantics, but you get Lagrange points with the simplest Kepler example, 1 body around the sun, or in other words, a 2 body interaction.

So the satellite is not orbiting Earth? What is the advantage of putting the satellite there, as opposed to a regular orbit?

The satellite, like everything in our solar system, is orbiting the sun.

The sun-earth L1 lagrange point is between the sun and the earth (in every two-body gravitational system there are 5 lagrange points, so there are earth-moon lagrange points etc)

These points are interesting because the orbit behaviour of items in them is weird! Specifically, the gravitational effects of the two bodies involved work in tandem to produce interesting effects.

Any bodies positioned at the L1 lagrange point of a two-body system will stay in the same position relative to both the larger bodies. Normally, the closer you get to the thing you are orbiting the faster you orbit. If you are appropriately near another large body (like the earth) that second body "pulls" back on you [edit: as long as you are on the inside of it - if you're on the outside it pulls you forward, and you get the L2 point], causing your orbit to slow down. At L1, those forces are balanced, and the third, smaller body has the exact same orbital period as the second body.

That is, the satellite is always on a straight line drawn between the earth and the sun.

The main reason for it to be there is to measure the solar wind, an early detection system.

It also happens to be in a great position to take pictures of the sunlit side of the earth.

Interesting, thanks. I understand that the satellite needs to have some form of propulsion to keep it at L1 (it is unstable), so it must have a limited life. How long?

From a Q&A session https://www.nasa.gov/content/goddard/qa-on-noaas-dscovr-miss...

The mission is slated for 2 years, and they have fuel for 5. I also happen to know that they reached L1 faster than anticipated thanks to a really nice insertion from the SpaceX Falcon 9 launch vehicle.

This means that the operational life might be even longer, but I haven't found any sources for what that might be.

It's nost just with Lagrange points. Actually, most of the satellites need to carry some fuel for station-keeping - the combined effects of non-uniform mass distribution in the orbited body, solar radiation, gravitational pull of other bodies and even air drag will slowly alter, or even completely degrade your orbit.

See [0] for more: https://en.wikipedia.org/wiki/Orbital_station-keeping

Every satellite needs to use propulsion for station keeping, satellites at LaGrange points included. Orbits aren't as stable in real life as they are in math.

L1 in particular is perfect for measuring the solar wind and Coronal Mass Ejections as an early warning system [0]. DSCOVR (the probe that took this photo) is the successor to ACE which is used to predict Auroras amongst other things [1]. This data is released by NOAA as a forecast [2]. I built an Aurora simulator with a similar API [3], but I think that mainly uses magnetometers.

[0] https://en.wikipedia.org/wiki/Lagrangian_point#Spacecraft_at...

[1] http://www.nesdis.noaa.gov/DSCOVR

[2] http://www.swpc.noaa.gov/products/aurora-30-minute-forecast

[3] https://unop.uk/dev/led-strip-aurora-alerts

Actually DSCOVR is a satellite that was supposed to be used for climate change research, but then Bush was elected... Though, this whole Sun monotoring thing is something that was added twelve years after the sattelite was done, an apparetly what got it flying

Unmanned NASA probes are Earth's selfie stick.

The probe that took this photo is the Deep Space Climate Observatory (DSCOVR) and it "was the first time a SpaceX rocket launched an object into deep space".

http://spaceprob.es/dscovr/

Why don't we see the Moon's shadow projected over the Earth in the pic? I guess it has to do with the relative distances of the 2 bodies to the Sun and the Moon's penumbra or something. Can someone make a digital image simulation of this to verify?

I thought the dark edge at the top-left of the moon was a shadow, but there was no solar eclipse in the time-frame reported for these pictures.

So, even though a perfect alignment of DSCOVR (at L1), the moon, and Earth would mean a shadow and thus eclipse, the moon must be a little off that alignment on this pass, throwing its shadow into dark space, even though it looks very nearly aligned in the photos.

That dark edge is an artefact of the delay in capturing the three monochrome pictures through the different RGB filters.

The article says : "Combining three images taken about 30 seconds apart as the moon moves produces a slight but noticeable camera artifact on the right side of the moon. Because the moon has moved in relation to the Earth between the time the first (red) and last (green) exposures were made, a thin green offset appears on the right side of the moon when the three exposures are combined. This natural lunar movement also produces a slight red and blue offset on the left side of the moon in these unaltered images."

It also says "A thin sliver of shadowed area of moon is visible on its right side." which is a better explanation. It's not a shadow on the Earth, it's the dark part of the moon.

The lunar orbit is inclined to Earth's ecliptic plane by 5.1°. That is enough to throw the shadow of the Moon outside the Earth most of the time (expect in cases of solar eclipses, which are rare)

When the moon casts a shadow on the earth we (on the surface) experience it as a solar eclipse.

For these images, the moon is not directly between the sun and the earth, so it cannot block sunlight from hitting the earth. So, no shadow.

But the satellite is at the L1 Lagrange point which is between the earth and the sun. So if you see the moon pass in front of the earth from L1 shouldn't the moon then also be directly between the earth and the sun? And as someone in another post noted: you can see the suns reflection in the ocean. And the moon passes directly over this spot.

All you can take away from the moon passing over the sun's reflection is this. The moon crossed over the sunlight reflected from the earth. To create a shadow, the moon must cross through the light emitted from the sun.

This image might better help explain. Since the earth's orbital plane is in a different xy plane than the moon's, the moon crossing over the reflection guarantees nothing about whether it crossed the sun's emitted light.

http://www.cnyo.org/wp-content/uploads/2014/04/2014april10_e...

Ah, yes of course. And as cyanoacry noted in another comment, the satellite isn't actually in the Lagrange point - it is orbiting it. Thanks for clearing that up.

Oh nice, ya, I didn't address the Lagrange point because I didn't have any knowledge of it.

One rarely sees earth and moon to scale at the correct distance. I think this leads many of us to often have a broken intuition about these things. And while these new images are spectacular, the distance between moon and earth is not obvious here. Look at e.g. [1]. It becomes immediately obvious why the shadow of the moon will only hit the earth rarely (during an eclipse). If it's not obvious, try holding two real objects at the correct scale / distance in your hands and make one throw a shadow on the other.

At scale, if the earth was the size of a basketball and the moon the size of a baseball, they would be about 7.5m apart.

[1] http://i.imgur.com/LbFGl96.jpg

What shadow? When is the last time you walked out the door in the daytime and it was dark because the the moon was casting a shadow? That only happens during eclipses.

DSCOVR actually is in a "halo orbit" around L1, which means it's not sitting in the plane of the Earth-Sun orbit. From the DSCOVR site[1]: "The spacecraft will be orbiting [L1] in a six-month orbit with a spacecraft-Earth-sun angle varying between 4 and 15 degrees."

As some other folks have mentioned, the Moon's orbit is tilted a total of 5.2 degrees[2] relative to the Earth-Sun plane, so DSCOVR will see quite a number of DSCOVR-Moon-Earth alignments, but never a Sun-DSCOVR-Moon-Earth alignment.

[1] http://www.nesdis.noaa.gov/DSCOVR/

[2] http://hyperphysics.phy-astr.gsu.edu/hbase/solar/solecl.html

Cool that California is so clearly visible.

Too bad you can see the multiple exposures, one for each of red, green, and blue, on the hi-res image. Otherwise it is quite the perfect picture.

What struck me about this was how huge the moon looks compared to the earth. We are used to seeing this as a small object in the sky (after all, it's 2000 miles across and 200000 miles away).

But when viewed from afar...you're seeing an object with an 8K mi diameter and another with a 2K mi diameter, not that different in size at all.

Which, I guess is another way to say: the earth just ain't that big.

These pictures were taken "only" 1,000,000 miles away, so the Moon is significantly closer to the camera than Earth was, which makes it appear larger compared to Earth than it really is. The true size comparison is more like [0]. The effect is also more because the

[0] http://qph.is.quoracdn.net/main-qimg-5bff56bc0b31f8b7395bdbe...

The relative sizes of objects in a photo like this will vary depending on whether you're close up and using a wider angle lens, compared to being far away with a very zoomy telephoto.

It approaches an "apples to apples" size comparison asymptotically as you move infinitely far away with an infinitely zoomed lens.

For a quick illustration: http://i.imgur.com/zME26IW.png

When you're up close, the moon obscures a much larger portion of the Earth, even though they're not changing size.

Honest question: Why don't the clouds seen on Earth show any activity or movement over the course of this time lapse?

It's only about 20 pictures at 30 second intervals each, which is only 10 minutes. From a million miles away, you wouldn't see noticeable changes in ten minutes. Much like when you are flying in a plane over the ocean and the waves look still.

The pictures were taken over 5 hours. You can see that the satellite is in a stationary position over the day side of earth.

There definitely is some movement:

Look at the fine features of the northern arm of the vortex in the South, they change quite a bit. Also, there are some clouds growing just east of the Gulf of California.

[EDIT] As it's arguably hard to spot with the low frame rate and movement I uploaded a stabilized and sped up version. It's centered on a cloud patch in the Pacific. You can now clearly see a cloud west of it disappear as well as a lot of movement in that jet stream(?) next to it.

http://i.imgur.com/Sg28xqu.gifv (legacy GIF 8MB: http://i.imgur.com/Sg28xqu.gif)

Closeup: http://i.imgur.com/wYfbnoU.gifv

If at all possible, please link to .gifv versions of imgur links; the .gif is a whopping 4.4 MB (compressed, 8.8 MB uncompressed), vs 737 KB as .webm in the gifv version.

TL;DR: do not use .gif as a video format.

CC: NASA

Wow that looks much better than the original.

Is this the real reflectance of the moon? Seems so dark.

Usually we see the moon at night surrounded by night sky, which probably skews our perception of the real color of the surface material.

According to TFA the earth is just so much brighter.

Yes, indeed. The eposure of the photo must have been set to make earth look as bright as we expect, and leaving the moon darker.

Yes, Earth's average albedo is around 0.3 while the Moon's is only around 0.12.

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

Probably because that's the Dark Side of the Moon?

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

Is that a joke? The dark side of the moon is not more often dark than the visible side. It is just never visible from Earth.

I'd suggest following the link that was posted.

"There's no dark side of the moon, really. Matter o' fact, it's all dark."

Thank you thank you thank you. I couldn't stop chuckling for at least five minutes.

I waited 24+ hours to respond because I didn't want to call undue attention to your comment. I didn't want anyone to downvote you for violating HN's unwritten proscript about humor.

The moon has approximately the same color as fresh asphalt, so it’s expected. It only looks bright on the night sky because everything else (including the stars) is just far darker.

Conversely, what I thought was pretty cool is seeing the reflection of the sun off the oceans, roughly in the middle of the earth 'disc'. You can see a fuzzy bright spot that stays in the middle of the disc as the earth spins.

Yes. I remember reading somewhere (Wikipedia probably) the moon is only about as reflective as asphalt, believe it or not. Imagine how much brighter moonlight would be if it were painted brilliant white (e.g. titanium dioxide pigment). I'd love to see a simulation. Would it be bright enough so we could see enough scattering that the sky would appear blue, I wonder.

Someone tweeted this yesterday and some of the replies were really disheartening.

Several people were calling it fake, with varying explanations of either "The earth is flat" or "Everybody knows the whole space program is fake".

I knew people out there actually believe this, but damn...

I find Twitter to be second only to YouTube in comment trolls.

I have to say that the images look like badly photoshopped fakes to me as well. If they weren't on a NASA page, I wouldn't believe them to be real.

Sometimes, reality is quite different from what we expect it to be.

Don't consider all comments to be honest, there are tons of bored trolls.

But also don't underestimate the stupidity, ignorance and/or anti-intellectualism of the general American (as well as other countries) population. Remember that 1/3 of Americans do not believe in evolution...

Why do you automatically think all or even most Twitter comments are from Americans?

Not all, just the dumb ones!

Also, two-thirds of native English speakers are in the US.

Nativity does not matter. Did you think I was a native speaker? I am not.

That was why I put "(as well as other countries)" on the comment; but I probably wasn't as clear as I could have been.

I specifically mentioned America because that's what I had the statistics around belief in evolution for. Also, I feel more qualified to comment on the "stupidity, ignorance and/or anti-intellectualism" of American's because I see/hear it every day.

I don't find these kind of replies disheartening. I think scepticism of NASA is a good thing. Because some of that scepticism might translate into new research, new developments, new experiments, and maybe even new entrepreneurial efforts in space.

Tobold is not describing rational skepticism of NASA's ability to fulfill its mission. Tobold is describing conspiracy theories and people who have fundamental misunderstandings of science.

Maybe if we discredit the last thousand-odd of years of scientific progress and history and start over from scratch, someone will discover magic and we can all fly to the moon on the back of aether turtles.

Moon is tidally locked to Earth, which is interesting. How long will this last? How long has this been going on? Does this happen to all satellites in all planets?

Another question: is the Moon orbiting plane aligned with the Earth rotation axis? Why or why not?

You can get the answer to all these questions by reading:

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

and:

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

The magic of reading!

Reading is the old-school local processing. Asking people is cloud computing, which is hot so it must obviously be better!

HN is becoming a free mechanical turk for reading.

So, the Moon orbiting plane is close to the ecliptic, and the satellite is in the ecliptic (L1 is in the ecliptic). I do not get this:

> About twice a year the camera will capture the moon and Earth together as the orbit of DSCOVR crosses the orbital plane of the moon.

(nitpick: the DSCOVR has no "orbit" around the Earth, since it is in the L1 point)

Since the Moon's orbit and the ecliptic are so close, I would expect this crossing to happen more often (on every turn of the Moon around the Earth)

DSCOVR is orbiting the sun and the earth at the same rate. In one year it will go once around the sun and once around the earth.

Interestingly, the moon's tidal lock is not perfect, resulting in a wobble that can be seen in time lapses: http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4236

I used to work in the SVS and Ernie, who made those images, got to be a real expert on the complexities of the moon's orbit. He did some really great work. Check out the SVS website for more.

What is the green "shadow" on the right of the moon? I'm not saying this is fake, but it looks like what I see in some greenscreen videos. I am really curious.

"EPIC’s “natural color” images of Earth are generated by combining three separate monochrome exposures taken by the camera in quick succession. EPIC takes a series of 10 images using different narrowband spectral filters -- from ultraviolet to near infrared -- to produce a variety of science products. The red, green and blue channel images are used in these color images.

Combining three images taken about 30 seconds apart as the moon moves produces a slight but noticeable camera artifact on the right side of the moon. Because the moon has moved in relation to the Earth between the time the first (red) and last (green) exposures were made, a thin green offset appears on the right side of the moon when the three exposures are combined. This natural lunar movement also produces a slight red and blue offset on the left side of the moon in these unaltered images."

You'd think they could be smarter about combining the R,G,B images. E.g., allow for the thing under each pixel to have moved a little from one image to the next, look at all their narrowband images (which will typically be strongly correlated, especially for nearby wavelengths) to estimate how fast each part of the image is moving, and then to get a pixel in the final image combine its G with slightly offset (maybe interpolated) R and B.

Fiddly but hardly, er, rocket science.

(Of course for some purposes you really need the unaltered R,G,B images. But if you're producing a single RGB JPEG image for public consumption, that's not one of those purposes.)

[EDITED to add:] More difficult, I guess, is dealing with things that appear in only some of the planes. E.g., if G is taken last then there will be bits of Earth at the trailing edge of the moon in the G frame that have no counterparts in the R,B frames because the moon occluded them in those frames. So there will still be artefacts in the image. But I'd have thought they'd be less objectionable than the ones you get from just naively stacking the R, G, and B.

It seems like you have re-discovered why segmenting the lunar image and shifting it backwards in time, to align the three color planes, was not done. They don't have the information to fill in the resulting gap, because it was occluded. In a very real sense, they have nothing to put in those pixels.

If they had wanted to do it, they could have. The ephemeris (i.e., basic imaging geometry relating to the location of Earth, Moon, and camera) will be very well-known. That bread-and-butter image processing is no problem.

The historical context here is that NASA centers, prominently JPL, were among the inventors of what became digital image processing (https://en.wikipedia.org/wiki/Digital_image_processing#Histo...).

Probably artifacts from the rgb channels not taken simultaneously.

I think it's chromatic aberration[1], it's an artefact of the lens. I'd be interested to know why this lens seems to suffer so much from it.

[1] https://en.wikipedia.org/wiki/Chromatic_aberration

Edit: apparently not based on other comments; will leave this here anyway.

Ha! Love the image file name "epicearthmoonstill"!

http://www.nasa.gov/sites/default/files/thumbnails/image/epi...

This is exactly the shot I've been hoping for since we got that first image of the Earth from DSCOVR. I tried to make an educated guess of how large the moon would appear from a million miles away, and I have to admit I far underestimated how large it would appear.

Everyone gets excited about a journey to Mars (and other manned spaceflight ventures), but NASA's unmanned probes are far and and way the best science its done.

What strikes me is the vastness of the oceans from above.

These pictures, at this angle, imply that the Earth regions under the moon were experiencing a solar eclipse, right? (Odd that the NASA article doesn't mention this.)

EDIT: There was no solar eclipse at the "last month" time-frame these pictures were taken. So that isn't a real earth-shadow under the leading edge of the moon, and as close as the moon seems to pass over the perspective-center of Earth, it must have actually been off somewhat, casting its shadow into space.

see discussion on this topic at https://news.ycombinator.com/item?id=10015354

Why aren't the stars more visible in the background? Does it have to do with the camera's exposure?

Earth is a sunlit object in this picture, the luminosity is the same level as during the day on earth - would you see stars in your photos if you took a correctly exposed photo of something during daylight on earth? I don't think this would happen :) The dynamic range difference between day light objects on earth and the stars on the sky is huge.

The satellite is 1 million miles away from Earth at the L1 Lagrange point. What is it about optics that allows us to compare a photo of the stars taken at such a distance with one taken from the surface of the earth? [Edit: "compare", in the sense of understanding whether or not the stars will or won't show up in each case. I get that the laws of optics are the same throughout the universe.]

> The dynamic range difference between day light objects on earth and the stars on the sky is huge.

I agree, but would a person sitting in the satellite see stars if they looked in that direction? If so, do our eyes just have better dynamic range than the camera used by the satellite?

Yes, our eyes just do have a fantastic dynamic range.

Having said that, if you were sitting on the satellite, you would see even more stars if you blinkered out the brightness of the sun, moon, and earth.

Don't cameras have much better dynamic range, but we just limit it in software by reducing everything into 8-12bit/color images? After all, the hardware is just a bunch of sensors counting photons.

Go here and see for yourself, for example: http://www.dxomark.com/Cameras/Nikon/D810---Measurements

ISO50, 14ev, ISO 12800 8ev. Then read here:

http://photo.stackexchange.com/questions/21579/how-does-the-...

We as humans can probably obtain 24 stops when our body uses all the tricks it has, not only optics of our "hardware".

Thanks for links here and under another comment, I learned something new today :).

>The satellite is 1 million miles away from Earth at the L1 Lagrange point. What is it about optics that allows us to compare a photo of the stars taken at such a distance with one taken from the surface of the earth?

The fact that the earth in the picture is lit by the sun and has similar luminocity levels to looking at the sky from the surface during the day.

The background of the picture (the stars) on the other hand, have the same meagre light they always have.

Eyes have about 24 stops dynamic range, there are sensors that have over 20 stops dynamic range with a single exposure, with multiple exposures (HDR) you can of course get way more than that.

The problem is that our monitors have very limited dynamic range - so even if the original had very high dynamic range, it would not show up properly on a current monitor.

There are HDR panels coming to the market this year which have more dynamic range.

And of course it's possible to tonemap HDR images for viewing on normal screens - there are various algorithms for that - https://en.wikipedia.org/wiki/Tone_mapping

Note that the Moon is fully lit by the Sun (it's a "full Moon" from the perspective of the satellite). And it's gray on the picture, as the Earth is significantly brighter.

Now, you can check it yourself, take the best camera you can have, go one night when the Moon is full somewhere outside of the city where you see the stars and then try to make a photo where on the photo both the stars and the Moon surface are visible at the same time. It simply can't work, the light of the stars is very faint, as soon as you see any details of the surface on the photo you take the stars will surely be invisible. Our eyes are still much better than any camera we can produce.

Isn't this just because of the processing? I imagine if you took additional logarithm of the values returned by the sensor, you could have both starts and the bright moon visible at the same time.

No, our bodies can simply do more, see:

http://photo.stackexchange.com/questions/21579/how-does-the-...

We could use additional "tricks" with cameras too (e.g. physically obscuring the moon and earth for one frame to shoot the stars then mixing it with the next photo) and with the additional post-processing (which would certainly include reducing the dynamic range to be able to show the photo on the screen) get something that some skeptics would think is "normal" but it's not what was being done on the photos presented, as nobody designs that much for features that actually don't bring anything: It would be easier to shoot just the sky in the same direction (the stars would look effectively the same, they are that far -- the satellite is just one hundredth of one AU away from the Earth and Alpha Centauri is some 271 thousands AU away) and photoshop it.

That's basically the idea behind HDR (High Dynamic Range) imagery in photography/photo processing. (And my understanding is that it's hard to figure out exactly what the best scaling function is in order to mimic typical human perception: it's not just a simple log.)

actual image http://cdn.phys.org/newman/gfx/news/2015/fromamillion.png

nasa website used up 20MB of mobile data then crashed my browser (stock android)

The image NASA links is actually a 3MB GIF

http://www.nasa.gov/sites/default/files/styles/full_width/pu...

My iDevices accidentally work with the NASA page. If your device crashes it's because of the other unfortunate "modern" web development practices that are really too resource heavy. Somebody inclined to analyze more can certainly find a lot of problems with their presentation (I see a lot of articles are on the same page, for example).

A lot of cool stuff on that site but annoying that they hijack the "back" button.

Should I be able to see Earth orbiting satellites in this picture?

How close are satellites to the spacecraft that took these photos? Well, it's about a million miles from Earth, generally the farthest satellites away from Earth are at about 40,000km altitude in geostationary orbit, which would put them maybe 4% closer to the spacecraft than Earth, so it wouldn't affect perspective hardly at all.

So that leaves resolution and physical size.

How big are satellites? About the size of cars or maybe a bus?

Can you see cars in this picture?

> it's about a million miles from Earth, generally the farthest satellites away from Earth are at about 40,000km altitude in geostationary orbit, which would put them maybe 4% closer to the spacecraft than Earth

No, that puts satellites in geostationary orbit 2.5% as close to Earth as the satellite that took this picture (in other words, it is 40 times as far away from Earth).

No more than you'd expect to be able to see a car, I don't think.

You mean like the moon? Yes.

You mean like meteosat? No. A 4 metre wide object is going to be such a small proportion of the size of a single pixel that it will be completely invisible.

Ok thanks.

Does anyone know why they decided to go with just a 4 megapixel camera?

I guess they could settle for taking more narrow images and recombining later but it seems better to take one image and crop if they are just interested in small parts.

Plus you have the option for digital zoom.

>Does anyone know why they decided to go with just a 4 megapixel camera?

I'd say because they have several other constraints the necessitate that, not because a 50MP wouldn't do. E.g. resistant to cosmic radiation, able to cope with the light extremes it needs to, etc.

Here they have some other factors I didn't consider: http://www.extremetech.com/extreme/134239-why-does-the-2-5-b...

Those are not iphone cameras, they need to work under extreme conditions and for a very long time. The camera must also have been chosen years ago.

It's also worth noting that the camera is quite old. The satellite was built in the late 90s, and was flown more-or-less unchanged when it eventually took to the sky.

So not only do you need to account for the space hardening that has gone into the technology (it was designed to keep working through the middle of a solar storm), you also have to take into account the state of the art over 15 years ago.

They are not even using the 4MB as it is. It takes time to download an image, and apparently they are more interested in what they call 'downlink cadence' - number of images per hour. I don't know enough about the science to say what the desired resolution would be - meaning, would a 50MB sensor actually produce better science for the mission of the DSCOVR (clearly it could be used for other science once you get the resolution good enough).

The specifics are here: http://www.nesdis.noaa.gov/DSCOVR/pdf/DSCOVR%20-%20EPIC%20In...

Also, DSCOVR was initially built for the Triana mission in the late 90s, and it's main purpose was just to serve live-ish images on the internet. (https://en.wikipedia.org/wiki/Deep_Space_Climate_Observatory)

It can take a decade to build a satellite. And you have to fix the design before you build it. And you don't usually fly the absolute latest toy; you fly something that's proven reliable. So by the time it's on station, a satellite might be flying 10-20 year old tech.

Oh good, there isn't a hidden civilization there. Whew.

The only thing I could think about was Iron Sky busted :D

This looks unreal.

Take an orange and a lemon and separate them two yards away.

That's how they'd look from space.

I always heard a basketball and a tennis ball 24ft apart.

"This is no moon!"

For anyone looking for the original link: http://www.nasa.gov/feature/goddard/from-a-million-miles-awa...

It seems it would have sense to change the link to point to the NASA's article. Moderators?

At your service.

URL changed from http://phys.org/news/2015-08-million-miles-nasa-camera-moon.....

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