Starship Asterisk*

alter-ego wrote:The separations of multiple object references yield a pixel angular resolution of ≈ 12.4", exactly the WAC. Therefore the sun would illuminate 15.8 pixels.

Edit: Of course the Sun is not in only one spot. Wrt Saturn, it drifts about 1° per hour. That's about 18.5 solar diameters per hour.

Nitpicker wrote:

Chris Peterson wrote:

MarkBour wrote:Thanks to all of you for the answers to several of my questions.
Based on Chris Peterson's advice, I plotted a 166-pixel diameter white disk about where I'd guess the sun was.

That was based on the pixel scale of the narrow field camera. From the image description, it sounds as if this composite may be at the scale of the wide field camera, in which case the Sun would appear ten times smaller. Since this is a composite, some other scale may have been used, as well. To be sure, we'd need to calculate the actual scale from some physical reference, like the known angle between a pair of planets.

I estimate the diameter of the Sun should appear as about 0.5% (half of one percent) of the apparent distance between Mars and Earth. (Based on the fact that from Saturn, Mars and Earth were separated at the time by ~10.8° and the Sun has an apparent diameter of 3.25 minutes of arc. This neglects the relatively small distance between Cassini and Saturn, which was about 10 Saturn diameters, not including rings.)

Chris Peterson wrote:

MarkBour wrote:Thanks to all of you for the answers to several of my questions.
Based on Chris Peterson's advice, I plotted a 166-pixel diameter white disk about where I'd guess the sun was.

That was based on the pixel scale of the narrow field camera. From the image description, it sounds as if this composite may be at the scale of the wide field camera, in which case the Sun would appear ten times smaller. Since this is a composite, some other scale may have been used, as well. To be sure, we'd need to calculate the actual scale from some physical reference, like the known angle between a pair of planets.

MarkBour wrote:Thanks to all of you for the answers to several of my questions.
Based on Chris Peterson's advice, I plotted a 166-pixel diameter white disk about where I'd guess the sun was.

Ann wrote: ... But fascinatingly, right "below" (to the south of) SAO 110928 is a considerably brighter star, HD 18909 (HIP 14176), mag about +8.2! The eighth magnitude star is quite red, too, with a B-V index of about +1.42, very nearly as red as HIP 13295. Why don't we see it? The declination of faint SAO 110928 is +08 29' 38.8", while the declination of HD 18909 is +08 28' 18.9". The right ascensions of both stars are very similar, too, at 03h 02m 48.64s and 03h 02m 49.47s, respectively. Why do we see the "upper", neutral-colored, very faint one, but not the "lower", brighter, quite reddish one?

Another star that "should" show up, but doesn't, is HD 18262 (HIP 13679). This is a sixth magnitude star (mag around 6.0), spectral class F7IV, B-V index about +0.48. It is located "between" Lambda Ceti and red HIP 13495, but "below" them, at declination +08 22 54.4. Is it hidden behind something, perhaps one of Saturn's rings?

Ann wrote:But fascinatingly, right "below" (to the south of) SAO 110928 is a considerably brighter star, HD 18909 (HIP 14176), mag about +8.2! The eighth magnitude star is quite red, too, with a B-V index of about +1.42, very nearly as red as HIP 13295. Why don't we see it? The declination of faint SAO 110928 is +08 29' 38.8", while the declination of HD 18909 is +08 28' 18.9". The right ascensions of both stars are very similar, too, at 03h 02m 48.64s and 03h 02m 49.47s, respectively. Why do we see the "upper", neutral-colored, very faint one, but not the "lower", brighter, quite reddish one?

Another star that "should" show up, but doesn't, is HD 18262 (HIP 13679). This is a sixth magnitude star (mag around 6.0), spectral class F7IV, B-V index about +0.48. It is located "between" Lambda Ceti and red HIP 13495, but "below" them, at declination +08 22 54.4. Is it hidden behind something, perhaps one of Saturn's rings?

Nitpicker wrote:I think that if you were to fit a straight line on the image, between Earth, Venus and Mars, you'd have a pretty good approximation to the Ecliptic plane. Based on that and the date of the image, I estimate Jupiter would be out of frame, above the top edge, somewhat to the left hand side.

alter-ego wrote:Very good! We agree once again!
Last night I spent some time inspecting the star field across the image and was impressed with faintness reached. The limiting magnitude reached 10⁺ magnitude. It's odd to see such faint stars next to such a normally dominantly bright planet, but being on the back side and in the Sun's shadow permits longer exposures to pick up both planet details and fainter stars.

Nitpicker wrote:

Ann wrote:I note that some of the point sources that in most cases are background stars are quite differently colored. There is a very reddish point source to the left of "Jupiter" [Tethys], and a quite blue point source still further to the left.

I think the red and blue point sources are:

Red: HIP 13495, mag 6.5, class M3.

Blue: Lambda Ceti, mag 4.7, class B6III.

(It also looks like the stars far beyond the ring system, around the perimeter of the image, were not captured.)

Ann wrote:I note that Venus, Earth and Mars appear to be "perfectly colored". Venus is brilliantly white, Mars is faintly reddish, and the Earth-Moon system is slightly blue. "Jupiter" (or Titan?) is sand-colored, which seems like a reasonable integrated color for a white and brownish striped body at five astronomical units from the Sun. So this is a perfect color picture, then?

owlice wrote:

Anthony Barreiro wrote:

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.

But this image isn't solely a NASA image.

Ann wrote:I note that some of the point sources that in most cases are background stars are quite differently colored. There is a very reddish point source to the left of "Jupiter" [Tethys], and a quite blue point source still further to the left.

Ann wrote:

Patrick60 wrote:Is that Jupiter at the lower left, visible as a disc at about 8 o'clock?

No one has commented on Patrick60's question so far. I, too would like to know what it is. To me it really looks a bit like Jupiter. And if it isn't Jupiter, then what is it? Titan?

I note that Venus, Earth and Mars appear to be "perfectly colored". Venus is brilliantly white, Mars is faintly reddish, and the Earth-Moon system is slightly blue. "Jupiter" (or Titan?) is sand-colored, which seems like a reasonable integrated color for a white and brownish striped body at five astronomical units from the Sun. So this is a perfect color picture, then?

I note that some of the point sources that in most cases are background stars are quite differently colored. There is a very reddish point source to the left of "Jupiter", and a quite blue point source still further to the left.

Ann

Patrick60 wrote:Is that Jupiter at the lower left, visible as a disc at about 8 o'clock?

Anthony Barreiro wrote:

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.

Nitpicker wrote:

MTD wrote: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.

I must confess to not understanding how that is possible. Does this mean that wherever the rings are unilluminated by direct sunlight, we cannot see them, but can effectively see through them onto the planet, where we can see ringshine from the illuminated parts of the rings?

MarkBour wrote:...
[*] Following along with the previous question, how coordinated is all of this stuff in the Saturn system? It would be too simple if the equator of Saturn were aligned to the Sun, the rings were right over the equator, and everything rotated together. But perhaps some things are aligned.

MarkBour wrote:...
[*] If Earth, Venus, and Mars were visible as small light disks from this location, does that imply that they were all farther away from Saturn at the time than the Sun? So that light could travel to them and then reflect back to Saturn? Or is it possible to see a planet that is between the Sun and Saturn? Perhaps at a great enough angle, even an object that is closer to Saturn than the Sun would be able to reflect and scatter light, and so be visible against the darkness of space.