APOD: The Moon's Saturn (2013 Apr 07)

[APOD Robot]

The Moon's Saturn

Explanation: Just days after sharing the western evening sky with Venus in 2007, the Moon moved on to Saturn - actually passing in front of the ringed planet Saturn when viewed in skies over Europe, northern Africa, and western Asia. Because the Moon and bright planets wander through the sky near the ecliptic plane, such occultation events are not uncommon, but they are dramatic, especially in telescopic views. For example, in this sharp image Saturn is captured emerging from behind the Moon, giving the illusion that it lies just beyond the Moon's bright edge. Of course, the Moon is a mere 400 thousand kilometers away, compared to Saturn's distance of 1.4 billion kilometers. Taken with a digital camera and 20 inch diameter telescope at the Weikersheim Observatory in southern Germany, the picture is a single exposure adjusted to reduce the difference in brightness between Saturn and the cratered lunar surface.

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[Boomer12k]

Neat looking...

:---[===] *

[MargaritaMc]

I liked today's Apod very much - not only the unusual images of the Moon and Saturn but also the links in the text. Especially the one linked to the words 'billion'. I thought that these two images were especially helpful.

First - the distance to the Moon

One million - roughly twice the distance in kilometres to the Moon

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Then, the distance to Saturn

One billion - one thousand million - roughly two thirds of the distance in kilometres to Saturn

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http://kokogiak.com/megapenny/nine.asp

Margarita

[fausto.lubatti]

Nice picture: Saturn looks so tiny compared to the Moon!

[cbergcberg]

Is Saturn actually where it appears? Would the moon have enough mass to gravitational lens the image in any way?

[moonstruck]

MargaratiMC's links made my head spin. At first I couldn't make heads or tails out of them, but then they started making a lot of cents .

[neufer]

Is Saturn actually where it appears? Would the moon have enough mass to gravitational lens the image in any way?

Saturn is slightly closer to the moon than it appears.

The Sun bends the light of stars by up to ~1.75 arcseconds.

However, the Moon bends the light
by only ~ 26 µas (microarcsecond).

Nevertheless, this will be within the power of Gaia to measure:

<<Gaia is a space observatory to be launched by the European Space Agency (ESA) in October 2013. The mission aims to compile a 3D space catalogue of approximately 1 billion stars, or roughly 1% of stars in the Milky Way. Successor to the Hipparcos mission, it is part of ESA's Horizon 2000 Plus long-term scientific program. Gaia will monitor each of its target stars about 70 times to a magnitude 20 over a period of 5 years. Its objectives comprise:

• determining the positions, distances, and annual proper motions of 1 billion stars with an accuracy of about 20 µas (microarcsecond) at 15 mag, and 200 µas at 20 mag
  
  more accurate tests of Albert Einstein’s general relativity theory
  
  detection of tens of thousands of extra-solar planetary systems
  
  capacity to discover Apohele asteroids with orbits that lie between Earth and the Sun, a region that is difficult for Earth-based telescopes to monitor since this region is only in the sky during or near the daytime
  
  detection of up to 500,000 distant quasars>>

[Chris Peterson]

Is Saturn actually where it appears? Would the moon have enough mass to gravitational lens the image in any way?

Any mass at all will alter the path of light around it. But the Moon has nowhere near enough mass to shift the apparent position of Saturn measurably. The deviation is only the tiniest fraction of a single pixel. So practically, yes, Saturn is where it appears. Except... it isn't. That's because Saturn is more than a light-hour away, so it is actually in a different spot than where we observe it. This is called the aberration of light, and has to be compensated for when determining where in the sky we will actually observe a Solar System body (and under certain conditions, stellar objects as well).

[Spoonbender]

This might be a stupid question, but, would Saturn be visible in a similar way from the moon?

[neufer]

This might be a stupid question, but, would Saturn be visible in a similar way from the moon?

Elaborate. ("a similar way" ?)

[LocalColor]

This might be a stupid question, but, would Saturn be visible in a similar way from the moon?

Don't pay attention to my answer, as we are not experts, but if you had a 20" telescope on the moon with no atmosphere, I would think Saturn would look about the same size but much sharper?

Love this photo - thank you Jens Hackmann.

[Chris Peterson]

Don't pay attention to my answer, as we are not experts, but if you had a 20" telescope on the moon with no atmosphere, I would think Saturn would look about the same size but much sharper?

Exactly. Optically, Saturn can be treated as being the same distance from both the Earth and the Moon.

[Spoonbender]

This might be a stupid question, but, would Saturn be visible in a similar way from the moon?

Elaborate. ("a similar way" ?)

I mean, would it be recognizable as Saturn with the naked eye?

[neufer]

I mean, would it be recognizable as Saturn with the naked eye?

Why would you think that it might not?

[Chris Peterson]

I mean, would it be recognizable as Saturn with the naked eye?

Without a telescope, it would look just the same to you as it would here on Earth. Some people with good vision are able to see Saturn as slightly out-of-round with their eyes alone, but most people simply see it as a bright star.

[MadisonMiss]

I don't get this "old photos" and repeats constantly showing up on APOD. You would think that they would want new submissions. I submitted a picture a while back (wasn't accepted). Probably would have, if it were not for all the repeats.

[Chris Peterson]

I don't get this "old photos" and repeats constantly showing up on APOD. You would think that they would want new submissions. I submitted a picture a while back (wasn't accepted). Probably would have, if it were not for all the repeats.

Sunday APODs are repeats, giving the editors a day off. It's a pretty simple system.

[ta152h0]

so Sundays are like " teacher is not in the classroom " day ?

[Beyond]

so Sundays are like " teacher is not in the classroom " day ?

haha, you could say that. However, if you were to start flying APOD paper planes around the room, or something else to upset the Asterisk* atmosphere, one of the Admins just may womp you aside the head head with a pan and you'd see stars.

[Vince S]

Wonderful....I'll never forget the first time I ever saw Saturn, through an 8" Celestron Telescope. I remember thinking, "Hey, it really does look like all the pictures!" It's so beautiful on it's edge like that...just how I saw it. The wonders of God's creations never cease to amaze me...

[owlice]

I don't get this "old photos" and repeats constantly showing up on APOD. You would think that they would want new submissions. I submitted a picture a while back (wasn't accepted). Probably would have, if it were not for all the repeats.

APOD receives ~ 10 images for every submission that is shown. Even if previous APODs were not shown, there still would not be enough room for every image submitted.

From the APOD FAQ:

Q4: Have some APOD pictures been run more than once?
A4: Yes. Many of our readers have been with us less than a year and are unaware of some really spectacular or important astronomy pictures. New information about old pictures is becoming available over the WWW. The text and links for rerun pictures will make use of this newly available information. So although the picture might be old, some of the text and links of each APOD will be new. Also, more web surfers have larger bandwidth connections, which allows us to post higher-resolution image files that can be transferred conveniently. Software to handle more sophisticated image file formats has also become more common, so the picture's size and/or format might be new. Lastly, rerunning APODs saves us time and helps us update our archive. In general, our rerun policy currently is to only rerun APODs more than one year old to keep the pictures relatively "new" to new APOD viewers. We will almost never rerun more than two pictures in any given week. So when you load the current APOD,it is still, most probably, a new picture.

Also from that page:

NASA has archived literally hundreds of thousands of space and astronomy related pictures

[neufer]

NASA has archived literally hundreds of thousands of space and astronomy related pictures

Having enough pictures is easy.

'Tweeting' an accurate yet understandable "Explanation" is hard: http://asterisk.apod.com/viewtopic.php? ... 14#p196681

[owlice]

NASA has archived literally hundreds of thousands of space and astronomy related pictures

Having enough pictures is easy.

'Tweeting' an accurate yet understandable "Explanation" is hard: http://asterisk.apod.com/viewtopic.php? ... 14#p196681

Pitching about others' writing is easy.

Writing for public consumption day in and day out for nearly 18 years is harder: http://apod.nasa.gov/apod/calendar/allyears.html

[BMAONE23]

Today's image is very similar to what I used to create my avatar

[StarCuriousAero]

I absolutely love this image! Quite happy that this one ended up as a repeat.