Starship Asterisk*

Pluto at Night

Explanation: The night side of Pluto spans this shadowy scene. The spacebased view with the Sun behind the distant world was captured by New Horizons last July. The spacecraft was at a range of over 21,000 kilometers, about 19 minutes after its closest approach. A denizen of the Kuiper Belt in dramatic silhouette, the image also reveals Pluto's tenuous, surprisingly complex layers of hazy atmosphere. The crescent twilight landscape near the top of the frame includes southern areas of nitrogen ice plains informally known as Sputnik Planum and rugged mountains of water-ice in the Norgay Montes.

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Once again, I am thrilled, and astounded, at how truly wonderful New Horizons has been: both incredible technically, and utterly fantastic in its target Pluto's cornucopia of wonders!

I did not appreciate sufficiently the view of Pluto from the rear when it was first released, probably because the sunlit images were so breathtaking. I now have the leisure to admire and wonder at the nightside image.

Excluding solar eclipse photos, which, as the name implies, we think of as images of the sun, not the moon, what bodies of the solar system have we photographed from the nightside? There can't be many, since most bodies would appear as black on black, nearly invisible, particularly if there is no atmosphere and lighting is dependent upon reflection from another body, an "earth" glow equivalent. The moons of Jupiter and Saturn seem like obvious candidates. Has Dawn attempted this with Vesta or Ceres?

Because some of Pluto's surface is visible in the thin crescent at the top, the geometry of this image did not have the sun directly behind Pluto, but somewhere obliquely off frame to the upper right? I know there was photography taken when Pluto occulted the sun, but they must have taken a series that lasted a few minutes as the spacecraft continued away and the sun emerged from eclipse. I'm going to have to search the image archive and find that sequence. That would make a mighty nice animation.

How long was the exposure? If you look closely, you'll notice short star trails.

Anobium wrote:
Excluding solar eclipse photos, which, as the name implies, we think of as images of the sun, not the moon, what bodies of the solar system have we photographed from the nightside? There can't be many, since most bodies would appear as black on black, nearly invisible, particularly if there is no atmosphere and lighting is dependent upon reflection from another body, an "earth" glow equivalent. The moons of Jupiter and Saturn seem like obvious candidates. Has Dawn attempted this with Vesta or Ceres?

• Many attempts...and a few successes:

darksky2500 wrote:Because some of Pluto's surface is visible in the thin crescent at the top, the geometry of this image did not have the sun directly behind Pluto, but somewhere obliquely off frame to the upper right? I know there was photography taken when Pluto occulted the sun, but they must have taken a series that lasted a few minutes as the spacecraft continued away and the sun emerged from eclipse. I'm going to have to search the image archive and find that sequence. That would make a mighty nice animation.

You are correct, the sun is not directly behind Pluto. If the atmosphere was thousands of times more dense, the sunlight might refract around to what would otherwise be in shadow, but Pluto's atmosphere is far too thin for significant refraction.

I did some quick math and when this image was taken, New Horizons was cruising past Pluto at a leisurely 18 kilometers per second...! I would suspect that with its camera trained on the ex-planet, any stars in the background would appear as short streaks.

It's an amazing little world, and even after seeing only one hemisphere it still had many surprises to behold.

Should be about as "dark as dark can get"....

Good-Niiiiiiiight, Plutoooooo.....
Nice Pic,

:---[===] *

Boomer12k wrote:
Should be about as "dark as dark can get"....

Good-Niiiiiiiight, Plutoooooo.....

Then this ebony bird beguiling my sad fancy into smiling,

By the grave and stern decorum of the countenance it wore,

"Though thy crest be shorn and shaven, thou," I said, "Art sure no craven,

Ghastly grim and ancient Raven wandering from the Nightly shore –

Tell me what thy lordly name is on the Night's Plutonian shore!"

Quoth the Raven "Nevermore."

Three words with so much more attached. Poe's death, like the passing of Pluto, left a few questions yet answered about mercury too.

To neufer..

My thanks for the nightside images… much appreciated!

[My computer "corrected" neufer to neuter. Wonderful things, computers.]

Anobium wrote:
My computer "corrected" neufer to neuter.

• What...me worry

neufer wrote:

Anobium wrote:
My computer "corrected" neufer to neuter.

• What...me worry

Art sure no craven! Neuter? Nevermore!

Bellerophon wrote:How long was the exposure? If you look closely, you'll notice short star trails.

This was a fun image to analyze - there's really more than one answer to your question.
The MVIC (Ralph) image was acquired by a time-delay integrated scanning technique using an array size = 5000 pixels x 32 pixels. Scanning was accomplished by a controlled (synchronized) rotation of the spacecraft along a direction perpendicular to the 5000-pixel row. Every 400ms the array was exposed to a new area. For this panchromatic image, the rate of craft rotation was 1600 microradians per second (each pixel = 19.77 microradians).
So all the star trails are the result of 0.4 second exposures, but the integrated 7295-pixel axis required 90 seconds of combined exposures.

Now the fun part: Over 90 seconds, the expected Pluto distortion is compression ≈ 2° (about 35% of its diameter!), and I was able to corroborate this by identifying the star field. In fact, I needed to compress the imaged star field along the scan axis (Right Ascension) by ~1.9° in order to match the correct star positions.

Thanks for the understanding