Shouldn't there be an eclipse if the moon goes between L1 and Earth?
The next eclipse is due in mid September.
A million miles out in deep space far beyond the Moon's orbit, closer in to the Sun, lies the L-1 Lagrange point. Here sits the DSCOVR spacecraft with its EPIC instrument pointed back at Earth. NASA has just released some EPIC images, showing the moon zipping past in front of Earth. Here they are: Moon transit of Earth. …
Indeed, and considering the side shown in the image is actuallz the brighter one - less basalt - it's really surprising how grey the old Moon really is.
Makes me wonder how things would have gone if we had something like ol' Enchiladas for a satellite, throwing shadows at night and all that.
How does that craft maintain its velocity around the sun to keep it close to the earth? There is so much that can go wrong but still it works and send pictures back. I just can't begin to think about what it takes to put something like that out there. The skills and tech blows me away.
"How does that craft maintain its velocity around the sun to keep it close to the earth?"
Gravity. It's at the Lagrange L1 point where the Earth's and Sun's gravity are about equal. They both help tug DSCOVR along. "Goresat's" orbit is similar to SOHO's (click de image links inside this one), but the cameras face toward Earth rather than the sun.
Well, not exactly. In that case neither the Sun nor the Earth would "pull" on DSCOVR and it would fly straight off tangentially. The actual L1 point is not where the two gravitational forces are equal, but as Wikipedia puts it "The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required to orbit with them". Not quite the same thing (incidentally, also explains why there are not one but five of them - the rest are definitely not anywhere gravitational forces alone could be "equal and opposite")... :)
"Seriously, that shadow on the right hand side of the moon? Photoshopped? Let the conspiracy theories commence!"
Note the specs on the camera.
DSCOVR's "EPIC" camera doesn't have a single color imaging mode. Instead, EPIC - like a lot of cameras on space probes - takes monochromatic images at different wavelengths. To get a color image, you combine those. EPIC works across 10 bands from near IR to UV and - important to your point about a "shadow" - takes only 10 shots an hour the bands being scanned in sequential intervals.
In short, you see a "shadow" because the moon is moving between the 10 different scans that make up one image. Notice how in enlarged views the "shadow" is actually green-ish?
Mega-close-up for the green "shadow":
Ah, here's some more accurate details about the green shadow and imaging process:
DSCOVR "snapped the photos that make up the new time-lapse video over a 5-hour span on July 16. Each image combines three single-color snapshots. That origin can be spotted in the photos, which show a faint green outline on the right side of the moon's disk due to the system's movement during the photographing process..."
A key point: this occurred about half a day after new moon. As seen from earth, both the moon and the spacecraft were about ten degrees from the sun. So the sunlight is coming in from behind the spacecraft and a little to its left (in the north-up frame of this image). Thus, the shadowing on the right limb of both the earth and moon.
Dunno much about the color part of this puzzle, but could easily imagine it being due to the earth being kept steady in the center of the picture while the moon was gradually moving.
I suspect that the NASA boffin didn't mean that he personally didn't know the Moon's albedo, more that most people find it surprising that it is so low because the only time they see the moon is against the background of space (albedo = 0.0000...). Compared to pure black, the moon looks white, so the natural assumption is that it has a fairly high albedo. I introduce the concept of albedo in a basic meteorology lecture, explain that the Earth's albedo is about 0.3 and ask the students to guess the albedo of the moon. Most of them go for values that are far too high. (The actual value is not all that well defined because it is strongly angle-dependent, as well as varying from place to place on the moon. But it is a lot lower than 0.3)
This animation is goddamned EPIC! hope the person who concocted that backcronym for the camera array got at least a pat in the back.
Of all the amazing space photos, from the pale blue dot to the Earth rise to Pluto's heart, this gif is got to be my new favorite.
I have to concur with an Anonymous Coward up there: it looks fake. I know it is not fake, but it is surreal seeing something as common as the Moon over the Earth, from "behind". It makes me think of that Victorian engraving of an alchemist sticking his head outside of the Fixed Stars Dome, and looking for the first time at the "hidden machinery" that makes the Universe work (Wikipedia tells me it's the Flammarion Engraving)... Breathtaking stuff
At any given time, 50% of the Moon is visible from Earth, and being tidally locked it is (nominally) the same 50%. When libration (correct word?) is taken into account, we can see about 59% of the lunar surface. DSCOVR will have perfect views (in many wavelength bands) many times, and could build up views of the Moon in each of those bands. As DSCOVR orbits L1 (and the Moon wobbles, and has tilt), how much of the lunar surface can eventually be seen by DSCOVR?
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