Astronomy Picture of the Day
February 18, 2014

On the Terminator (Part II)
On the Terminator (Part II)

Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington and Dr Paolo C. Fienga/LXTT/IPF for the additional process. and color.

This new (and, once again, really wonderful) image, taken by the NASA - MESSENGER Spacecraft still on December, 9, 2013 (just like yesterday's APOD), shpws us the Mercurian Terminator Line (such as the "Transition Area" between the Day-side of Mercury and its Night-side). An Astronaut which were standing on Kosho Crater's still illuminated Central Peak - at the time this image was taken - would see the Sun setting over an extremely dark and uneven Local Horizon.

As usual, and just out of curiosity, the frame featured in yesterday's APOD (which showed part of an area located just to the North of Kosho Crater - whose diameter is approx. 65 Km - such as about 40,365 miles - across), was taken immediately before this one. Last, but not least, and as we already mentioned yesterday, even the area that surrounds Kosho Crater, as well as its ancient and highly degraded Rim, as you can see, has been litterally "showered" (---> intensely covered) by Secondary Impact Craters (such as Rocky Debris, all belonging to the Mercurian Surface, after it was subject to a - probably very long - series of subsequent Impact Events).

Date acquired: December, 9th, 2012
Image Mission Elapsed Time (MET): 28935228
Image ID: 5350994
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 60,08° North
Center Longitude: 223,0° East
Solar Incidence Angle: 91,6° (meaning that the Sun, at the time that the picture was taken, was already set, by about 1,6°, below the Datum (Zero Altitude) of the imaged Local Mercurian Horizon - center of the frame)

Emission Angle: 50,4°
Sun-Mercury-Messenger (or "Phase") Angle: 142,0°

This picture (which is an Original NASA - MESSENGER Spacecraft's b/w and NON Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 16998) has been additionally processed, contrast enhanced, Gamma corrected, magnified to aid the visibility of the 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 - MESSENGER Spacecraft and then looked outside, towards the Limb of Mercury), 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 other things, the existence of different Elements (Minerals) present on the Surface of Mercury, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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