Starship Asterisk*

This may be just a very simple answer but I have always wondered one thing: this picture and the previous one which exists of the earth from the moon, why are there no stars in the background?

http://antwrp.gsfc.nasa.gov/apod/image/ ... ga_big.jpg
I'm not positive but the amount of light from the moon and the Earth probably overwhelms the amount of light coming from the stars. It does make a beautiful background for my computer screen though.
Orin

In the description accompanying the APOD for 2007-11-20, the statement is made that "An astronaut standing on the lunar surface would never actually see the Earth rise..." Due to libration, this statement is not quite accurate. An astronaut in a region near the "edge" of the Moon as seen from Earth would, in fact, see the Earth rise briefly for a few days each month. Rather than moving across the sky to set at the opposite horizon as celestial objects are observed to do from Earth, however, the Earth would be seen to rise only a few degrees above the horizon (at most), then sink back toward it.

Perhaps someday that sequence of images will be featured as a animation on the APOD.

I noticed the nickname of the lunar satellite (Kaguya) is misspelled in the the title of the blurb. Must have been written by a Twilight Zone fan. Referring to Cayuga Productions.
--Randy

Does the earth-rise picture not look a little odd? The foreground shadows indicate a light source on the left, bit the indistinct limb on the earth in the background indicates the light source is on the right.

Also it looks like north is "up" on the earth although it is difficult to tell for sure because of the size of the image. That would mean that the space craft was orbiting over the moon's poles. I suppose there is no scientific reason for this to not be the case... but the shadows still seem suspicious to me.

kmh

kptnfmrs wrote:Does the earth-rise picture not look a little odd? The foreground shadows indicate a light source on the left, bit the indistinct limb on the earth in the background indicates the light source is on the right...

In both the foreground and background, it appears to me the light source is behind and a little to the right of the observer.

http://antwrp.gsfc.nasa.gov/apod/ap071120.html

SELENe is indeed orbiting over the poles (90 degrees inclination). The polar orbit gives complete coverage of the moon as it slowly rotates beneath the orbiter.

MCinAZ, that would be a pretty sequence of images to see. Or perhaps a composite image showing the earth's analemma as viewed from the moon.

I got curious about the spectacular crater in the foreground. I turned up a list of lunar craters over 50 km diameter and sorted it for latitude. After poking around for a few minutes, I'm pretty well convinced it is Plaskett Crater.

http://the-moon.wikispaces.com/Plaskett#tocPlaskett1



The central mountains and other features all appear to be a match.

I had a friend look at the photo and his opinion was that it was the earth's reflection as the light source and thus the shadows seem to be cast by an object in the distance.

It all makes sense, now.

kmh

I've posted a simulation:

http://www.aslc-nm.org/EarthRise.mov (15.0 Mb)

or

http://www.aslc-nm.org/EarthRiseMed.mov (3.1 Mb)

It's 'taken' from near the Demonax Crater

Enjoy!

rr

MCinAZ wrote:In the description accompanying the APOD for 2007-11-20, the statement is made that "An astronaut standing on the lunar surface would never actually see the Earth rise..." Due to libration, this statement is not quite accurate. An astronaut in a region near the "edge" of the Moon as seen from Earth would, in fact, see the Earth rise briefly for a few days each month. Rather than moving across the sky to set at the opposite horizon as celestial objects are observed to do from Earth, however, the Earth would be seen to rise only a few degrees above the horizon (at most), then sink back toward it.

Perhaps someday that sequence of images will be featured as a animation on the APOD.

badsocref, the simulation is amazing. I really appreciated it. Although, my question has not been explained, can anyone? Do the publishers of APOD just take the stars out?

Jdempse6 wrote:badsocref, the simulation is amazing. I really appreciated it. Although, my question has not been explained, can anyone? Do the publishers of APOD just take the stars out?

No. The image is exposed to show the Earth and the lunar surface, which are many, many times brighter than the stars. The stars are simply so underexposed that they are invisible. Go out some night when there is a full Moon and take a picture of it. You won't see any stars in the image.

If they set the gain on the camera high enough to show stars, the Moon and Earth would both be completely blown out.

Looks like someone corrected the spelling of Kaguya in the title of the blurb. But they still missed a typo: "starting" should be "started" near the middle of the blurb.

Jdempse6 wrote:badsocref, the simulation is amazing. I really appreciated it. Although, my question has not been explained, can anyone? Do the publishers of APOD just take the stars out?

I do a fair amount of astrophotography. When photographing the moon, most cameras do not have the dynamic range to capture both the moon and stars. The Earth should be many times brighter than the Moon, so the lack of stars would be natural. The human eye has a much higher dynamic range than CCD (or CMOS) cameras, so we can see both the moon and surrounding stars, but to do this with a camera requires multiple exposures and a fair amount of playing with the images.

Hope this helps.

btw - I re-'shot' the simulation and will post it later today (same link). I dimmed the stars significantly to make it look more realistic, and added some clouds to the Earth's surface.

rr

Here's a way to think about it...

The moon is in the sun. What I mean is that the moon is bathed in sunlight, as though it were a ball you might hold in your hand in the middle of the day. Even though it's rather a dull gray color that doesn't reflect much light (they say it's about like an asphalt road surface), the light level reflected off it is simply brilliant as compared to the light from the stars.

Your eyes have immense dynamic range. Much larger than even the best cameras. Thus you can perceive both detail in the moon and see the stars while looking up at the sky.

However, chances are you can't easily see stars right next to the moon, as even your eyes are subject to flare and a reduction of light input when looking at bright objects (contraction of the iris).

Photographers know that photos of the moon are like photos in the day time - shutter times are usually a small fraction of a second. Shutter times for photos of the stars, on the other hand, are usually measured in minutes.

-Noel

OK perhaps I'm just a moron... wouldn't the "earthrise" once a month due to the phases of the moon?

mr_halstead wrote:OK perhaps I'm just a moron... wouldn't the "earthrise" once a month due to the phases of the moon?

I think that would be sunrise. My understanding is that since the same face of the moon is always facing earth, the earth would always appear at the same location in the moon's sky.

Bystander is correct. You would notice Earth Phasing during the month, and a slight placement shift over the month much like the moon experiences over the course of a month like the lunation APOD shows. But the earth would remain in the same area of the sky when viewed from the moon. Earth Rise is only accomplished from orbit.

A few weeks ago I didn't have a clear understanding of the moon's orbit. Now that I do, I am curious… Does anybody know why the moon is situated the way it is? By that I mean that its orbit is tilted about 5 degrees from the ecliptic with the earth tilted roughly 23 degrees in its rotation to the ecliptic. I know it provides a good angular size for eclipses and I expect this position has bearing on how the tides work. But would life on earth be different if the moon’s orbit angle was different… say the moon's orbit was also tilted in line with earth's rotational tilt at roughly 23 degrees to the ecliptic for example?

I understand why the earth is positioned where it is but how critical is it that the moon be positioned and moving about in its present orbit?

CuriousEd

emc wrote:I am curious… Does anybody know why the moon is situated the way it is? By that I mean that its orbit is tilted about 5 degrees from the ecliptic with the earth tilted roughly 23 degrees in its rotation to the ecliptic.

Everything in the Solar System (inside the Oort Cloud) is largely on the plane of the ecliptic, but tweaked out of that plane a bit by billions of years of chance events- collisions, near misses, and gravitational perturbations. The Moon is no different. There are any number of ways it could have gotten where it is, and probably being the product of a massive collision itself, it's hardly surprising to find some inclination from the ecliptic.

I understand why the earth is positioned where it is but how critical is it that the moon be positioned and moving about in its present orbit?

Not at all critical, I think. There are good reasons to think that the Moon played a key role in the development or the evolution of life on Earth, because of the tidal zones it produces at land-sea boundaries. But the Moon used to be closer; it's getting farther away and slowing down the Earth's rotation. These effects have apparently been minor in the grand scheme of either geology or biology. The Moon could be in a wide range of inclinations, both nearer and farther from the Earth, and still produce tides substantially similar to what we have had in the past, and continue to have today.

Thanks for responding Chris. You are good at explaining things.

I was not aware of the Oort cloud, so thanks for that too!

You have helped me toward my objective which was to learn if anyone in the scientific community sees the moon’s positioning as evolved by design. In other words, is there any evidence of a designed cosmic system from the scientific point of view?

Besides the moon, earth and sun, system can also be the solar system or the galaxy and so on.

Best regards,
Ed