Astronomy Picture of the Day
November 6, 2013

On the Limb (Part II)
On the Limb (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.

What a difference a simple and plane week can make on Mercury! In fact, the frame that we decided to feature in today's APOD, was acquired - always by the NASA - MESSENGER Spacecraft - on October, 9, 2013, which means just 1 (one) week after the picture that we showed you in yesterday's APOD (and titled "On the Limb" - Part I).


Today's frame, however, shows us how the so-called "Lighting Conditions" on Mercury can dramatically change in just one Earthly week (which, remember, is only about 4% - four-per-cent - of a full Mercurian Day). If you click on the image, so that you can bring it to its full dimension, and then watch VERY carefully the Mercurian Landscape, you will (should...) still be able to spot the Unnamed Impact Crater with its (at least) four "controversial" (as far as their nature is concerned) Crater Chains that we watched and discussed yesterday.


Now, with the Sun quite a bit higher above the Horizon where the aforementioned Unnamed Impact Crater is located (and that, anyway, you can find at about a quarter of the way up from the bottom of the frame), you may be able to notice that its Floor appears kind of smooth, while its Crater Chains can still be seen to stretch from it, far away, from its Outer Rim.


Date acquired: October, 9th, 2013
Image Mission Elapsed Time (MET): 23629938
Image ID: 4974132
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 43,49° South
Center Longitude: 150,40° East
Solar Incidence Angle: 77,7° (meaning that the Sun, at the time that the picture was taken, was about 12,3° above the imaged Local Mercurian Horizon)
Emission Angle: 57,7°
Sun-Mercury-Messenger (or "Phase") Angle: 132,9°


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 17621) 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 down, 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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