Astronomy Picture of the Day
June 23, 2013

Nightfall on Dione...
Nightfall on Dione...

Credits: NASA/JPL/Space Science Institute - Credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/IPF

In this beautiful and recent view of the Saturnian moon Dione, we can just see a dimly illuminated (and therefore highly suggestive) slice of this Celestial Body; in fact, the picture was taken by the NASA - Cassini Spacecraft just when the Surface of Dione was slowly slipping from daytime into the night. Just out of curiosity, you have to know that any (obviously future) "resident" of Dione, would always have plenty of time to read a few bedtime stories, and that is why the moon's Rotation Period is considerably long (of course when compared to our Earthly standards): in this case, we are talking about something like 66 hours!

Dione, which is the fourth-largest moon of the Gas-Giant Planet Saturn, is approx. 700 miles (such as about 1126,53 Kms. The lit Terrain seen in this picture is located on the Anti-Saturn Side of Dione; North is up and rotated 10° to the left. The image was taken in Visible Light with the NASA - Cassini Spacecraft Narrow-Angle Camera on March 30, 2013. The view was acquired at a distance of approximately 684.000 miles (such as about 1.100.788,56 Million KiloMeters) from Dione and at a Sun-Dione-NASA - Cassini Spacecraft , or Phase, Angle of 108°. Image scale is roughly 4 miles (such as about 6,43 Km) per pixel.

This frame (which is an Original NASA - Cassini Spacecraft b/w frame published on the NASA - Planetary Photojournal with the ID n. PIA 14665) has been additionally processed, contrast enhanced, magnified to aid visibility of the Surface details and then colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Cassini Spacecraft and then looked outside, towards the Saturnian moon Dione), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Dione, each having a different Albedo (---> Reflectivity) and Chemical Composition.

Note: it is possible (but we, as IPF, have no way to be one-hundred-percent sure of such a circumstance), that the actual luminosity of Dione - as it is in this frame - would appear, to an average human eye, way lower than it has been shown (or, better yet: interpreted) here.

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