Starship Asterisk*

stephinity wrote:
Fantastic APOD! I have a question though: I dont quite understand what's going on with the light of the rings in Saturn's shadow. If the backside of Saturn is being partially lit up by light reflected off the rings, why are the inner rings curved up so much, whereas the others seem aligned (with their rings light up directly by the Sun)? Any thoughts? Thanks!

Torillion wrote:
Thanks, neufer, for the explanation, but I'm afraid I still don't get it. Perhaps it's because I don't know what a night side equator is and can't find a good explanation. Any chance you could explain it?

• 1) the full set of back-lit rings on the left & right with
  2) the lit up backside of Saturn
  as obscured by just the A & B rings.

• 1) a dark obscuration due to the B ring and
  2) a fainter obscuration due to the A ring.

• 1) a bright Southern Hemisphere
  (due to backlighting from the rings)
  2) a fainter Northern Hemisphere
  (due to scattering from the rings) and
  3) a thin dark equatorial line
  (that receives no light at all from the thin rings).

APOD Robot wrote: in this exaggerated color image.

bystander wrote:

---

PIA08324: Pale Blue Orb

"The Earth-and-moon system is visible as a bright blue point on the right side of the image above center. Here, Cassini is looking down on the Atlantic Ocean and the western coast of north Africa. The phase angle of Earth, seen from Cassini is about 30 degrees."

Credit: NASA/JPL/SSI

APOD Robot wrote: in this exaggerated color image.

PIA08329: In Saturn's Shadow

[url=http://photojournal.jpl.nasa.gov/catalog/PIA08324][size=120][b][i]PIA08324: Pale Blue Orb[/i][/b][/size][/url]

---

---

Not since NASA's Voyager 1 spacecraft saw our home as a pale blue dot from beyond the orbit of Neptune has Earth been imaged in color from the outer solar system. Now, Cassini casts powerful eyes on our home planet, and captures Earth, a pale blue orb -- and a faint suggestion of our moon -- among the glories of the Saturn system.

Earth is captured here in a natural color portrait made possible by the passing of Saturn directly in front of the sun from Cassini's point of view. At the distance of Saturn's orbit, Earth is too narrowly separated from the sun for the spacecraft to safely point its cameras and other instruments toward its birthplace without protection from the sun's glare.

The Earth-and-moon system is visible as a bright blue point on the right side of the image above center. Here, Cassini is looking down on the Atlantic Ocean and the western coast of north Africa. The phase angle of Earth, seen from Cassini is about 30 degrees.

A magnified view of the image (inset) taken through the clear filter (monochrome) shows the moon as a dim protrusion to the upper left of Earth. Seen from the outer solar system through Cassini's cameras, the entire expanse of direct human experience, so far, is nothing more than a few pixels across.

Ann wrote:
The image you showed in your post is not the right side of the image above center. And the inset can't be from that image, since the inset is clearly in black and white.

By the way, I did notice that today's APOD was produced from ultraviolet, infrared and "clear" filters, which means two invisible filters and one that won't show color. There can be little doubt, however, that the Earth looks blue from space, and if possible it should be shown as such, I think.

neufer wrote:

---

Torillion wrote:
Thanks, neufer, for the explanation, but I'm afraid I still don't get it. Perhaps it's because I don't know what a night side equator is and can't find a good explanation. Any chance you could explain it?

You are confusing :

• 1) the full set of back-lit rings on the left & right with
  2) the lit up backside of Saturn
  as obscured by just the A & B rings.

While the two seem to have superficially similar structures they are actually quite distinct and they are clearly separated in the APOD near the outer edge of Saturn itself (as if someone had drawn a half circle in black marker around the bottom of Saturn).

On Saturn's surface all you can really see is two simple ring bands:

• 1) a dark obscuration due to the B ring and
  2) a fainter obscuration due to the A ring.

Ignore those two obscuring bands and what you see on Saturn is

• 1) a bright Southern Hemisphere
  (due to backlighting from the rings)
  2) a fainter Northern Hemisphere
  (due to scattering from the rings) and
  3) a thin dark equatorial line
  (that receives no light at all from the thin rings).