APOD: Earth and Moon from MESSENGER (2010 Sep 01)

[drollere]

i didn't vote for this image and regret that it was posted because it grossly misrepresents both the relative sizes of the earth and moon (because the moon has a higher albedo) and grossly misrepresents the earth/moon distance relative to size.

image size of earth = 11 pixels
image size of moon = 5 pixels
actual earth diameter = 7926 miles
therefore, actual moon diameter = 7926 * 5/11 = 3600 miles OH SO WRONG!

earth based pixel scale = 7926/11 = 720 miles
image separation earth/moon = 12 pixels
therefore, earth/moon orbital distance = 720*12 = 8647 miles OH SO WRONG!

i've attached an image below that shows the correct proportions without image flare and/or the conjectural, post hoc suggestion of orbital foreshortening.

when you have viewers who dwell on the flattening of the earth on one side, without noticing that all the star images are elongated vertically, you realize the importance of posting astronomical images that do not invite gross misinterpretation, especially when the picture commentary makes no attempt to correct them.

[Tinak]

This picture would have been really cool if amateurs like me could have put their cursor on the screen to see the constellations. We always see the view looking from earth, not looking at earth. It just would have given a better bearing. Still a very cool pic!

[Ann]

drollere wrote:

i didn't vote for this image and regret that it was posted because it grossly misrepresents both the relative sizes of the earth and moon (because the moon has a higher albedo) and grossly misrepresents the earth/moon distance relative to size.

As for the relative albedo of the Earth and the Moon, it is actually the other way around. The Earth is much, much more reflective than the Moon. The Moon's surface consists entirely of dark rocks and dark dust, whereas the atmosphere of the Earth is highly reflective due to all the white clouds there. The Earth's albedo is about 42% whereas the albedo of the Moon is only about 7%.

So not only does the Earth reflect more Sunlight than the Moon because the Earth is bigger than the Moon, but the Earth also reflects about six times as much Sunlight than the Moon for each square unit of its visible "face".

Ann

[owlice]

i didn't vote for this image and regret that it was posted because it grossly misrepresents both the relative sizes of the earth and moon (because the moon has a higher albedo) and grossly misrepresents the earth/moon distance relative to size.

image size of earth = 11 pixels
image size of moon = 5 pixels
actual earth diameter = 7926 miles
therefore, actual moon diameter = 7926 * 5/11 = 3600 miles OH SO WRONG!

earth based pixel scale = 7926/11 = 720 miles
image separation earth/moon = 12 pixels
therefore, earth/moon orbital distance = 720*12 = 8647 miles OH SO WRONG!

i've attached an image below that shows the correct proportions without image flare and/or the conjectural, post hoc suggestion of orbital foreshortening.

when you have viewers who dwell on the flattening of the earth on one side, without noticing that all the star images are elongated vertically, you realize the importance of posting astronomical images that do not invite gross misinterpretation, especially when the picture commentary makes no attempt to correct them.

My interpretation of the image is that space is large, and Earth so very small. Our beautiful planet is significant only to us, only to the life teeming on it. Our small home is alone; we have nowhere else to go. As small as the Earth is in space, we are smaller still, as irrelevant to Earth over time as Earth is to the universe.

That is some of what I get out of the image. It is a beautiful photograph, stark, awe-inspiring, thought-provoking.

Keep your pixel counts; I take instead the grandeur of space, the fragility of our little island home, the beauty of our even smaller companion. Such riches in a photograph! How fortunate I am to see it!

[BMAONE23]

i didn't vote for this image and regret that it was posted because it grossly misrepresents both the relative sizes of the earth and moon (because the moon has a higher albedo) and grossly misrepresents the earth/moon distance relative to size.

image size of earth = 11 pixels
image size of moon = 5 pixels
actual earth diameter = 7926 miles
therefore, actual moon diameter = 7926 * 5/11 = 3600 miles OH SO WRONG!

earth based pixel scale = 7926/11 = 720 miles
image separation earth/moon = 12 pixels
therefore, earth/moon orbital distance = 720*12 = 8647 miles OH SO WRONG!

i've attached an image below that shows the correct proportions without image flare and/or the conjectural, post hoc suggestion of orbital foreshortening.

when you have viewers who dwell on the flattening of the earth on one side, without noticing that all the star images are elongated vertically, you realize the importance of posting astronomical images that do not invite gross misinterpretation, especially when the picture commentary makes no attempt to correct them.

What it shows is their relative brightness at the distance specified. As for the separation problem, the Moon was more than likely not at its maximum apparent distance from the Earth. It could have been in front of the Earth relative to the camera position thereby making it appear both too close and too bright.
I have to agree with Owlice's comments about our respective size and living options. We do have only 1 planet we can thrive on in our entire solar system, only 1 that is still hospitable to our form of life, and the next closest star system is much too far away to travel to given our current transportation limitations and understanding of physics.

[Ann]

That was a lovely post, Owlice.

Ann

[Billie]

RE: the appearance of the Moon so close to Earth
I was disappointed that APOD didn't explain that the proximity of the Moon only appeared so close because of its placement in its orbit. The actual distance of 30 Earth Diameters between us and our satellite is one of the biggest misconceptions I deal with in public outreach programs. Then here comes this photo with the Dynamic Duo "confirming" that misconception that it is snuggled up close to us.

[biddie67]

owlice - I agree with Ann - wonderfully stated .....

[emc]

At least I have my wheelbarrow… (Thanks Orin!)

Ed; you remember that?

Easy to recall… your wheelbarrow adventures reminded me how much fun it is to be a kid. I very much enjoyed you sharing that.

BTW - I think your “Resident Geezer” nickname chould change to “Hyperteria Monokyklou Star Pilot”… or perhaps “Envisage Astroventurer” if they are trying to keep the nicknames short.

[emc]

Right after I posted my comment I went, duh!

I know the feeling! Been there, done that.

I prepared this response and although others beat me to the punch, I decided to post it anyway, in case it helps and to find out if I’m correct… (I hope someone will post a correction if this is wrong)

The Moon’s Earth orbit is nearly on plane with Earth’s solar orbit… (The Moon orbit is inclined by 5.1 degrees to the ecliptic.) Today’s APOD Messenger photograph is taken from what you could call a side view near the ecliptic. Therefore, the Moon orbit from the camera’s perspective travels across the Earth left to right in front and right to left behind our planet (if my bearings are correct...). This picture just happens to catch the Moon “appearing” to be closer to the Earth than actuality.

[emc]

My interpretation of the image is that space is large, and Earth so very small. Our beautiful planet is significant only to us, only to the life teeming on it. Our small home is alone; we have nowhere else to go. As small as the Earth is in space, we are smaller still, as irrelevant to Earth over time as Earth is to the universe.

That is some of what I get out of the image. It is a beautiful photograph, stark, awe-inspiring, thought-provoking.

Keep your pixel counts; I take instead the grandeur of space, the fragility of our little island home, the beauty of our even smaller companion. Such riches in a photograph! How fortunate I am to see it!

Owlice, I enjoyed your post very much. You eloquently put into words what I felt when I first saw the image.

[Coincidence?]

Earth appears a little flattened on the left (non-Moon) side, as though it were a small ball of clay that had been made, put down on a table, and then picked up and positioned for this family portrait, table-side to the left. !

I noticed that, and then the proportions nagged at me. It looks surprisingly similar to a fuzzy view of a plot of the Mandelbrot set.

[Chris Peterson]

Would the earth / moon pair be visible to the naked eye from this position? Or would one need binoculars or telescope?

No, if you were seeing this with your unaided eye, you would not be able to resolve the pair. Earth in this image is only 14.3 arcseconds across, and the Earth-Moon outer separation is only 24 arcseconds. That is less than the resolving power of your eye (which is about 60 arcseconds). You could easily see the pair in binoculars, however. In this image, the Earth and Moon are in conjunction; at other points of the Moon's orbit you would easily be able to see the Earth and Moon as separate points of light. Neither would be big enough to resolve as a disc, however.

[Chris Peterson]

Earth appears a little flattened on the left (non-Moon) side, as though it were a small ball of clay that had been made, put down on a table, and then picked up and positioned for this family portrait, table-side to the left.

Although the image caption suggests otherwise, the Earth does show phases as viewed from Mercury- just as all the outer planets show phases as seen from Earth. While superior (outer) planets will never show the full range of phases, and therefore will never appear as true crescents, they certainly show enough phase to appear out-of-round. When this image was made, the Earth as seen from MESSENGER had an 11.2° phase. So the slight flattening (I measure about 7%) is to be expected. Good eye.

[Chris Peterson]

Earth in Cancer. I think the bright star to the right is Aldebaran.

If Earth was in Cancer from the viewpoint of MESSENGER, there's no way Aldebaran (in Taurus) could possibly be in the same image. It would be far out of the field of view.

Getting the scale from this image is difficult. The MESSENGER site claims the image was produced with the wide angle camera, which is 1024x1024 pixels and has a 10.5° FOV. That translates to a scale of 37 arcsec/pixel. At this scale, the Earth would be smaller than a pixel. If the image was actually made with the narrow angle camera, the scale would be 5.3"/pixel, which still seems quite far off. Judging by the size of the Earth, the scale seems to be around 1"/pixel. So it is very unclear to me just what we are seeing here.

[Chris Peterson]

I would've thought that the blue planet would appear a bit blue?

It might if this weren't a black and white image <g>.

[mexhunter]

Hello Owlice:
Your words leave a good taste of inspiration.

If Earth was in Cancer from the viewpoint of MESSENGER, there's no way Aldebaran (in Taurus) could possibly be in the same image. It would be far out of the field of view.

Getting the scale from this image is difficult. The MESSENGER site claims the image was produced with the wide angle camera, which is 1024x1024 pixels and has a 10.5° FOV. That translates to a scale of 37 arcsec/pixel. At this scale, the Earth would be smaller than a pixel. If the image was actually made with the narrow angle camera, the scale would be 5.3"/pixel, which still seems quite far off. Judging by the size of the Earth, the scale seems to be around 1"/pixel. So it is very unclear to me just what we are seeing here.

Chris:
Very good information and data about the camera's Messenger.
Regards
César

[neufer]

Earth in Cancer. I think the bright star to the right is Aldebaran.

If Earth was in Cancer from the viewpoint of MESSENGER, there's no way Aldebaran (in Taurus) could possibly be in the same image. It would be far out of the field of view... it is very unclear to me just what we are seeing here.

May 6, 2010: MESSENGER from the viewpoint of Earth using [url=http://space.jpl.nasa.gov/][b]NASA's Solar System Simulator[/b][/url]

---

In fact, on May 6, 2010 it was MESSENGER that was in Taurus (below & to the right of the Pleiades) from the viewpoint of Earth according to NASA's Solar System Simulator =>

So the Earth (from MESSENGER's viewpoint) should really be near the ecliptic to the right in Scorpius (6 months away from Taurus).

At first I thought that it was Beta Scorpii, a.k.a. Graffias but that doesn't seem quite right. In any event, it can't be a planet.

[JAW]

i didn't vote for this image and regret that it was posted because it grossly misrepresents both the relative sizes of the earth and moon (because the moon has a higher albedo) and grossly misrepresents the earth/moon distance relative to size.

Long time viewer first time poster, but yes, either the commentary should have mentioned the moon was close to being in front of the earth (ie the relative sizes and distances) or this image should not have been posted for general consumption. I had to think about what that picture meant for quite a while before I got it - and I consider myself the next step up from "mostly harmless" when it comes to stuff like this.

Enough to drive me to post about it! Which is a sad endictment on society; because I have enjoyed my daily dose of APOD for many years, and always look forward to it - and I've never said anything until I didn't like one! So sorry fellas, I love what you do, but this one is along the path of the Mars hoax!

(I'll be more positive next time )

[phumphreys]

Randy and Ann,

I had the same question and I don't think it's a bad one. At 1/4 phase (half illumination) we should see a separation of about 30 Earth diameters. I'd like to know the actual date of the photo to check this - as shown this would have to be just a day from full phase or new phase for the scale to be right.

Paul

[Chris Peterson]

If Earth was in Cancer from the viewpoint of MESSENGER, there's no way Aldebaran (in Taurus) could possibly be in the same image. It would be far out of the field of view... it is very unclear to me just what we are seeing here.

May 6, 2010: MESSENGER from the viewpoint of Earth using [url=http://space.jpl.nasa.gov/][b]NASA's Solar System Simulator[/b][/url]

---

In fact, on May 6, 2010 it was MESSENGER that was in Taurus (below & to the right of the Pleiades) from the viewpoint of Earth according to NASA's Solar System Simulator =>

So the Earth (from MESSENGER's viewpoint) should really be near the ecliptic to the right in Scorpius (6 months away from Taurus)...

It looks like the angle between the Earth, Sun, and MESSENGER is about 12°, so that is almost one full month of difference, or one zodiacal constellation.

When I said I didn't know what I was seeing here, I wasn't referring to the sky itself (although I don't, in fact, recognize the background), but to the nature of the image itself, which seems to show a scale that is not consistent with the instrument that is reported to have produced it.

[orin stepanek]

BTW - I think your “Resident Geezer” nickname chould change to “Hyperteria Monokyklou Star Pilot”… or perhaps “Envisage Astroventurer” if they are trying to keep the nicknames short.

I've gotten fond of Resident Geezer; it seems to fit.
I really like today's picture! It's a photograph taken from Messenger; so it has to be; (in my humble opinion;) accurate. I applaud APOD for posting it.

[Ann]

Chris wrote:

When I said I didn't know what I was seeing here, I wasn't referring to the sky itself (although I don't, in fact, recognize the background), but to the nature of the image itself, which seems to show a scale that is not consistent with the instrument that is reported to have produced it.

Ah, I smell a rat here! I smell a Pulitzer! The revelation of the big Space Scam! Messengergate!

Ann

[Chakolate]

I hope this isn't too stupid a question, but why are there never phases of Earth from Mercury? It is because Mercury's orbit is so close to the sun? I tried figuring it out with a light bulb and a couple of balls, and got nowhere.

Thanks,
Chak

[bystander]

I had the same question and I don't think it's a bad one. At 1/4 phase (half illumination) we should see a separation of about 30 Earth diameters. I'd like to know the actual date of the photo to check this - as shown this would have to be just a day from full phase or new phase for the scale to be right.

According to the MESSENGER web site, the image was acquired on 06 May 2010. It also states the field of view is 10.5°.

Your estimate of 30 Earth diameters assumes the Moon is directly out to the side and not approaching the front or back of the Earth. It also does not allow for the brightness of the objects which would cause them to appear larger than actual size.