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Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Sat Aug 08, 2015 10:49 pm
by alter-ego
Remo wrote:Almost, but not quite. Indeed, the Moon's right edge is green and the left edge is purple because of the time delay in between camera exposures; however, the Earth's right edge is blue because we are looking at the edge of the atmosphere (
http://www.spaceflight.nasa.gov/gallery ... 20073.html ). The Earth's right side edge would be blue too, except for the fact that it is in darkness.
The thing is that the Moon is moving with respect to the camera, but the Earth is fixed (it does rotate slightly, however). This is because the Deep Space Climate Observatory satellite orbits at the L1 Lagrange Point: Basically a stable orbit directly between the Earth at the sun. Because the camera is fixed with respect to the Earth, you get the same big ball in the same place each time. Thank you (almost) President Al Gore.
As an aside, I find it interesting that the satellite's position on July 16th was not quite in perfect alignment. This is evidence by both the Moon and the Earth having a dark edge on the right side. Also interesting is that only this slight misalignment/dark edge allowed the green edge artifact to show up. The green filter was shot first. By the time the blue and red filters were shot, the Moon had moved towards the right and those images just recorded black thus allowing the green tint image of the earth below to be superimposed on top of the black Moon edge creating the green edge effect.
Both the Earth and Moon are 99% illuminated .
DSCOVR is not at the exactly at L1 - it is "orbiting" nominally about it in a
halo /
Lissajou orbit. If we define the L1 point to be exactly on a line connecting the Earth and Sun, then the DSCOVER-Earth line is off by ≈ 11.5°. This puts the craft about 200,000 miles (325,000km) from an ideal single-point L1 location. Also, in the time-lapse video, the Moon was directly between DSCOVR and Earth at about 22:00UT, Jul 16. New Moon was 1:24UT the same day, so the Moon was already 20½ hours old. These related factors are what's behind the 99% illumination fraction, thus the darker limb edge(s).
In fact the red filter was used first, and the green filter last. The green edge logically follows from the direction the moon is traveling (to the right). This is also described
here.
I recreated this event using Stellarium. It took a little time because I had to create DSCOVR's orbital location (but not the actual orbit as there are no elements available and the halo orbit is complicated). Anyway, from this simulation I determined where the craft was wrt the L1 point location.
![Stellarium Simulation - DSCOVR, Jul 16, 19:50UT + 5 Hrs](./download/file.php?id=19306&sid=7f6167ba787d12df02b119c8c3e6e0d1)
- Stellarium Simulation - DSCOVR, Jul 16, 19:50UT + 5 Hrs
- DSCOVR Moon-Earth View from L1_2.gif (3.11 MiB) Viewed 11970 times
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Sat Aug 08, 2015 10:56 pm
by alter-ego
owlice wrote:alter-ego, the "Discuss" link on the APOD page points to the wrong discussion, is all; for today's APOD, it points to yesterday's discussion.
I didn't see that, but I noticed that on the Curiosity main page, if you back-arrow to get to Earth, you go to Pluto instead (skips a day).
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Sat Aug 08, 2015 11:32 pm
by hoohaw
alter-ego wrote:jambo wrote:I thought some one would have corrected the discussion by now--it's the repeat of Friday's APOD, rather than Saturday's view of Mars...
I'm not sure what your saying. Friday's and Saturday's APODs are distinct; Earth and Mars respectively. Having issues with links maybe?
I have looked repeatedly all day and found NO Mars page, just repeat of previous day's comments. Weird! And I wanted to make a brilliant Mars comment, too!
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Sun Aug 09, 2015 1:57 am
by Chris Peterson
hoohaw wrote:alter-ego wrote:jambo wrote:I thought some one would have corrected the discussion by now--it's the repeat of Friday's APOD, rather than Saturday's view of Mars...
I'm not sure what your saying. Friday's and Saturday's APODs are distinct; Earth and Mars respectively. Having issues with links maybe?
I have looked repeatedly all day and found NO Mars page, just repeat of previous day's comments. Weird! And I wanted to make a brilliant Mars comment, too!
Yeah, the "Discuss" link on the Saturday APOD points to the wrong discussion (this one). But it shouldn't be too hard to find the Mars image discussion by looking at the parent forum for this one. If you need help, look
here.
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Mon Aug 10, 2015 5:07 pm
by Lometron
There is something I don't understand:
The picture was taken from a craft placed on the L1 Lagrange point. So the earth, the craft and the sun are on the same line.
We can see the moon on the earth. So the earth, the moon and the craft are on the same line.
So the earth, the moon and the sun are aligned.
The NASA says that the moon was new on the 16th July. But it's not enough: During a new moon, the moon should appear under or above the earth.
If the moon is in front of the earth, it means there is a solar eclipse. But there was no solar eclipse on the 16th of July. ( the last solar eclipse was on the 20th of March and the next one will be on the 13th of September)
Is this picture real?
Did I write something wrong above?
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Mon Aug 10, 2015 5:40 pm
by neufer
Lometron wrote:
There is something I don't understand
See above :
http://asterisk.apod.com/viewtopic.php? ... 50#p246790
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Mon Aug 10, 2015 8:55 pm
by pferkul
Since people so "enjoyed" the cross-eyed 3-D image of Pluto from yesterday, here is a 3-D movie I made from the images taken by NASA's Deep Space Climate Observatory.
https://www.youtube.com/watch?v=v3KJI1HVx_k
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Tue Aug 11, 2015 3:23 am
by alter-ego
Lometron wrote:
...
The NASA says that the moon was new on the 16th July. But it's not enough: During a new moon, the moon should appear under or above the earth.
If the moon is in front of the earth, it means there is a solar eclipse. But there was no solar eclipse on the 16th of July. ( the last solar eclipse was on the 20th of March and the next one will be on the 13th of September)
Is this picture real?
Did I write something wrong above?
The Moon and DSCOVR are indeed south of the ecliptic plane (geocentric ecliptic coordinates) by almost ~4.5°. So, assuming orbital symmetry, DSCOVR's halo orbit takes the craft north and south of the ecliptic by at least this much. It may be similar to SOHO's "orbital" motion - highly elliptical in two projected planes: the ecliptic (XY) plane and the plane perpendicular to it (YZ).
![halo_orbit.gif (59.23 KiB) Viewed 11881 times SOHO orbital insertion & halo orbit](./download/file.php?id=19311&t=1&sid=7f6167ba787d12df02b119c8c3e6e0d1)
- SOHO orbital insertion & halo orbit
BTW Art, thanks for your helpful timely response.
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Tue Aug 11, 2015 6:24 pm
by MrMak
Second, I wonder about that curious break in the cloud pattern in the Pacific positioned above the moon. I’ve been looking at satellite photos for decades and I don’t think I’ve ever seen a cloud break that was so artificial looking, made up of right angles and rectangles.
I presumed that this shadow, cast on (Earth) clouds above the Moon was from the Space Station.
Re: APOD: Full Moon, Full Earth (2015 Aug 07)
Posted: Tue Aug 11, 2015 6:34 pm
by Chris Peterson
MrMak wrote:Second, I wonder about that curious break in the cloud pattern in the Pacific positioned above the moon. I’ve been looking at satellite photos for decades and I don’t think I’ve ever seen a cloud break that was so artificial looking, made up of right angles and rectangles.
I presumed that this shadow, cast on (Earth) clouds above the Moon was from the Space Station.
The ISS isn't large enough to cast an umbral shadow. It's just a cloud pattern, albeit a rather odd one.