Starship Asterisk*

In the Shadow of Saturn

Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn drifted in giant planet's shadow earlier this year and looked back toward the eclipsed Sun. Cassini saw a unique and celebrated view. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, Saturn's expansive ring system appears as majestic as always even from this odd angle. Ring particles, many glowing only as irregular crescents, slightly scatter sunlight toward Cassini in this natural color image. Several moons and ring features are also discernible. Appearing quite prominently is Saturn's E ring, the ring created by the unusual ice-fountains of the moon Enceladus and the outermost ring visible above. To the upper left, far in the distance, are the planets Mars and Venus. To the lower right, however, is perhaps the most wondrous spectacle of all: the almost invisible, nearly ignorable, pale blue dot of Earth.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

Highest resolution version without annotation here:
http://photojournal.jpl.nasa.gov/figure ... 2_fig1.jpg

Highest resolution version with more detailed annotation here:
http://photojournal.jpl.nasa.gov/figure ... 2_fig3.jpg

They're in the description links but just in case you missed them.

With a father like Ouranos, I always knew Saturn would have a beautiful backside. Thank you again, APOD, Asterisk, Cassini Imaging Team and everyone else involved in making it possible to behold this incredible image.

Naturally, I have a question, but I wouldn't call it a nitpick this time, and most certainly not a criticism. It is just a bona fide question from a curious admirer. I have just read a more detailed description of this image here:
http://www.ciclops.org/view/7699/The-Da ... miled?js=1

But I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

An amazing image. Simply amazing!

The annotation says "Earth and Moon" and points to a white dot.

To me, that says that they both are where pointed, but I can't seem to find the Moon near the Earth. Maybe it's behind the Earth? But that is unlikely.

Therefore, I'd prefer the annotation to only mention the Earth. If somebody doesn't understand that this implies the Moon is "somewhere in the vicinity", then that's outside the scope of annotations for this picture.

Nitpicker wrote: ... But I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

It is not an instantaneous effect. It's as you said, due to combination of hundreds (141 of 323) images taken over 4 hours.

gwrede wrote:The annotation says "Earth and Moon" and points to a white dot.

To me, that says that they both are where pointed, but I can't seem to find the Moon near the Earth. Maybe it's behind the Earth? But that is unlikely.

Therefore, I'd prefer the annotation to only mention the Earth. If somebody doesn't understand that this implies the Moon is "somewhere in the vicinity", then that's outside the scope of annotations for this picture.

Both the Earth and Moon are visible in the highest resolution (not annotated) picture:

Always an awesome sight...the beauty of the Solar System...and the concept of looking back at us is just amazing!!!

:---[===] *

alter-ego wrote:

Nitpicker wrote: ... But I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

It is not an instantaneous effect. It's as you said, due to combination of hundreds (141 of 323) images taken over 4 hours.

Thank you alter-ego. That's good enough for me. I've noticed that every time we've attempted to correct each other previously, I was wrong and you were right.

Is that Jupiter at the lower left, visible as a disc at about 8 o'clock?

I saw this in the email announcement from ciclops.org and I am in absolutely gobsmacked at the resolution and clarity. This image is my favorite: Saturn 38754, but only because it's got everything labeled.
(The unlabeled images are uber-fabulous too.)

Two thumbs way up for the Cassini Team!

Patrick60, according to the image in this link, I believe what you're asking about is one of Saturn's moons, Tethys.

Nitpicker wrote:But I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

I figured it's the shadow of the planet, projected onto the ring particles. Since Cassini was inside the umbra, the shadow projection would appear larger than the planet itself. Of course, I can count on someone to teach me something new if I'm wrong.

Cousin Ricky wrote:

Nitpicker wrote:
I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

I figured it's the shadow of the planet, projected onto the ring particles. Since Cassini was inside the umbra, the shadow projection would appear larger than the planet itself. Of course, I can count on someone to teach me something new if I'm wrong.

It is certainly the shadow but it shows up only above Saturn because the Sun is slightly below the point directly behind Saturn.

The Sun is almost a point source at this distance and will not produce a noticeable penumbra at this resolution.

A serious contender for my all-time favourite solar system image. Wow !!

Nitpicker wrote: ... I've noticed that every time we've attempted to correct each other previously, I was wrong and you were right.

Well, in this example I thought I was just agreeing with you

The moon can be seen by most PC users by maximizing the image and then magnifying the image further by using key strokes of "control +". Use your slide bars on the side and bottom to locate Earth. Try it, you'll like it.

alter-ego wrote:Both the Earth and Moon are visible in the highest resolution (not annotated) picture:

Note, however, that neither object is resolved. Both are optical point sources, and the apparent sizes are purely a function of diffraction and their relative brightnesses. The NAC camera used has a pixel scale of 1.2 arcseconds; on the date this image was made, the Earth subtended 1.8 arcsec, and the Moon subtended 0.5 arcsec.

neufer wrote:

Cousin Ricky wrote:

Nitpicker wrote:
I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

I figured it's the shadow of the planet, projected onto the ring particles. Since Cassini was inside the umbra, the shadow projection would appear larger than the planet itself. Of course, I can count on someone to teach me something new if I'm wrong.

It is certainly the shadow but it shows up only above Saturn because the Sun is slightly below the point directly behind Saturn.

The Sun is almost a point source at this distance and will not produce a noticeable penumbra at this resolution.

The black crescent is Saturn's shadow on the half of the rings closest to Cassini. The shadow shows up only above Saturn because the rings below Saturn are on the other side of Saturn from Cassini's point of view, closer to the Sun, where Saturn can't cast a shadow.

The thin white ring that encircles Saturn is sunlight shining through Saturn's upper atmosphere. The black crescent shadow appears on the outside of the thin ring of atmosphere because the crescent shadow is the shadow of Saturn on the rings closest to Cassini. Parts of the thin ring are less bright because it's blocked by shadows cast by the rings, on the lower half of Saturn, or by the rings themselves, on the upper half.

Nitpicker wrote:
I still cannot figure out the narrow black crescent which outlines the top of the planet, and how it appears on the outside of the thin white ring of light which virtually encircles the planet. Is this an instantaneous effect, or the consequence of combining hundreds of component images taken over a period of four hours?

MTD wrote:

neufer wrote:

Cousin Ricky wrote: I figured it's the shadow of the planet, projected onto the ring particles. Since Cassini was inside the umbra, the shadow projection would appear larger than the planet itself. Of course, I can count on someone to teach me something new if I'm wrong.

It is certainly the shadow but it shows up only above Saturn because the Sun is slightly below the point directly behind Saturn.

The Sun is almost a point source at this distance and will not produce a noticeable penumbra at this resolution.

The black crescent is Saturn's shadow on the half of the rings closest to Cassini. The shadow shows up only above Saturn because the rings below Saturn are on the other side of Saturn from Cassini's point of view, closer to the Sun, where Saturn can't cast a shadow.

The thin white ring that encircles Saturn is sunlight shining through Saturn's upper atmosphere. The black crescent shadow appears on the outside of the thin ring of atmosphere because the crescent shadow is the shadow of Saturn on the rings closest to Cassini. Parts of the thin ring are less bright because it's blocked by shadows cast by the rings, on the lower half of Saturn, or by the rings themselves, on the upper half.

Okily Dokily.

Absolutely amazing image, and in natural colors. Is there a way to get a print of it, preferably in its highest resolution? I'd love to have it up on my office wall to stare and marvel at.

quigley wrote:Absolutely amazing image, and in natural colors. Is there a way to get a print of it, preferably in its highest resolution? I'd love to have it up on my office wall to stare and marvel at.

It would be a simple matter to download the high resolution TIFF file provided and get it printed using any of a number of online print services. You could also save it to a CD or a flash drive and take it to your local print shop.

quigley wrote:Absolutely amazing image, and in natural colors. Is there a way to get a print of it, preferably in its highest resolution? I'd love to have it up on my office wall to stare and marvel at.

All NASA images are in the public domain. You could download a high resolution image and take it to your local print shop or use an online printing service to make yourself a poster-sized print. You could even add an inspiring quote, and sell prints online. I might buy one.

Just don't say... The Uranus side of Saturn, or something similar.

Every time I look at this image, I'm intrigued by the fact that some of the rings seen against the dark face of Saturn do not line up with the rings as seen against the background of space. I understand that the rings between Cassini and Saturn are being illuminated by light reflected and perhaps refracted from the rings that are in direct sunlight. But it tickles my mind to notice that I automatically try to decide where the rings "really" are.