The Earth behind the Moon

[michel123456]

At first I thought it was fake but then I went to the Nasa site and saw this animation of the Moon passing in front of the Earth.

 

http://www.nasa.gov/feature/goddard/from-a-million-miles-away-nasa-camera-shows-moon-crossing-face-of-earth

 

 

And then i thought, if the satellite is always facing the daylight on Earth, it means the sun is behind. And if the sun is behind, doesn't that mean that this is actually a solar eclipse going on?

[swansont]

The three can be slightly misaligned (no eclipse) and still look like this.

[imatfaal]

Even if there were an eclipse it would be very unlikely to see it.

 

From the amount of turn we see (about a quarter) then I would estimate that was about 6 hours, in 20 frames, so a frame shot ever 18 minutes. The longest you can get totality is about 7 minutes.

 

The disc you can see of the earth is about 12500km - the size of the umbra is around 150-250 km wide.

And as the sun is almost directly behind us - then the eclipse would be covered from view by the moon anyway

 

BTW - great find; that really is an epic video

Edited July 28, 2016 by imatfaal

[swansont]

Even if there were an eclipse it would be very unlikely to see it.

 

From the amount of turn we see (about a quarter) then I would estimate that was about 6 hours, in 20 frames, so a frame shot ever 18 minutes. The longest you can get totality is about 7 minutes.

 

 

 

Excellent point. Plus, the darkened area would be behind the moon.

[Janus]

If you look closely at the video you will note that both the Moon and Earth are lit from an angle that is a bit to left of the camera view point. ( that thin black line on the right limb of the Moon is that part of the Moon unlit by sunlight.)

Also, it apparent from the relative apparent sizes of the Moon and Earth in this video that it was taken from a distance quite a bit further from the Earth than the Moon is from the Earth. ( the relative image sizes are very close to the actual relative sizes of the two, and this only happens if the picture is taken from far enough away.) This makes the moon and Earth look closer together than they would normally, just like a distances seem to be compressed by a telephoto lens. Thus that slight angle difference between camera and Sun would result in the Moon's shadow missing the Earth by quite a bit even though it doesn't look like it would in the video.

[michel123456]

Even if there were an eclipse it would be very unlikely to see it.

 

From the amount of turn we see (about a quarter) then I would estimate that was about 6 hours, in 20 frames, so a frame shot ever 18 minutes. The longest you can get totality is about 7 minutes.

 

The disc you can see of the earth is about 12500km - the size of the umbra is around 150-250 km wide.

And as the sun is almost directly behind us - then the eclipse would be covered from view by the moon anyway

 

BTW - great find; that really is an epic video

I thought the size of the umbra would be the same as the size of the Moon, taken that ray lights coming from the sun are parallel.

And there was no eclipse at this date

These images were taken between 3:50 p.m. and 8:45 p.m. EDT on July 16

 

[Janus]

For the umbra to be the same size as the Moon, the Sun would have to be the same size as the Moon like in the top image of the attachment below. (Image is not to scale, but the general argument still holds.)

Since the Sun is larger than the Moon, the Umbra tapers away as a cone. If you are further than the apex of the cone from the Moon, you are outside the Umbra, and at best you see a partial eclipse.

 

 

 

[swansont]

The result being that the umbra is at most 267 km wide (if the eclipse is at perigee)

http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/eclipses.html

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

[michel123456]

For the umbra to be the same size as the Moon, the Sun would have to be the same size as the Moon like in the top image of the attachment below. (Image is not to scale, but the general argument still holds.)

Since the Sun is larger than the Moon, the Umbra tapers away as a cone. If you are further than the apex of the cone from the Moon, you are outside the Umbra, and at best you see a partial eclipse.

 

 

 

umbra.jpg

I see.

 

So it must have been something like the below (I have stolen your diagram and add the Earth & the camera)

Where the path of the Moon is perpendicular to the diagram's sheet of paper in such a way that the umbra is constantly missing the Earth.

[imatfaal]

I see.

 

So it must have been something like the below (I have stolen your diagram and add the Earth & the camera)

Screen Shot 07-29-16 at 10.32 AM.JPG

Where the path of the Moon is perpendicular to the diagram's sheet of paper in such a way that the umbra is constantly missing the Earth.

 

Exactly - but to add the point that the separation distances are hugely under represented on that diagram; to the extent that I don't think the human eye could discern hit or miss. The sun is c.360 times further away than the moon and c.400 times larger - these almost balance so that apparent disc size from earth varies between 31-32 arc minutes for the sun and 29-33 arc minutes for the moon

[Janus]

More to scale, the Moon. umbra and Earth would look like this.

 

 

Just a 1 degree difference between Sun and view-line would result in the umbra missing the Earth.

[michel123456]

Doesn't that mean that the satellite (the camera) is not exactly in the line between Earth and Sun?

[swansont]

Doesn't that mean that the satellite (the camera) is not exactly in the line between Earth and Sun?

 

 

Yes. But that's been pointed out at least twice already.

[michel123456]

 

 

Yes. But that's been pointed out at least twice already.

I expected someone to give a reason for that.

The satellite is supposed to have reached its planned orbit at the first Lagrange point or L1, about one million miles from Earth toward the sun.

 

So the question goes, isn't L1 exactly on the line between Earth's center and Sun's center?

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

 

And also Nasa's statement

EPIC maintains a constant view of the fully illuminated Earth as it rotates

 

Is it accurate? Since the camera is not aligned upon the axis?

[Janus]

I expected someone to give a reason for that.

The satellite is supposed to have reached its planned orbit at the first Lagrange point or L1, about one million miles from Earth toward the sun.

 

So the question goes, isn't L1 exactly on the line between Earth's center and Sun's center?

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

It isn't exactly at a L1, it is in a halo orbit around L1, which means it is not perfectly in line between Earth and Sun.

And also Nasa's statement

Is it accurate? Since the camera is not aligned upon the axis?

Not perfectly, There are even visual clues to this in the video. The right limb of the Moon shows a dark line. We know this can't be the shadow of the Moon cast on the Earth, so it is that part of the Moon not being lit by the Sun. Also you will note that the right limb of the Earth looks different from the right limb. This is another indication that the sunlight is coming from a slightly different direction then that from which the image was taken.