Astronomy Picture of the Day
October 11, 2014

Delacroix and Shelley
Delacroix and Shelley

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.

Two large and highly degraded Impact Craters dominate this view of the Southern Hemisphere of Mercury (the scene is approx. 230 Km - such as about 142,83 miles - across), obtained by the NASA - MESSENGER Spacecraft on October, 17, 2011. The top one is Delacroix Crater. As you can see, the Southern Rim of Delacroix Crater cuts the Northern Rim of Shelley Crater, thus indicating that Shelley Crater is older. Both Impact Craters are, however, very ancient, with battered Rims and interiors (---> Floors) that have suffered countless impacts and got infilled with (probably) Volcanic and/or Ejecta Material.

Shelley Crater has been named after Percy Bysshe Shelley (who was born in Horsham - UK -, on August, 4, 1792 and died in Lerici - Italy - on July, 8, 1822), an important English Romantic poet. His poem "Ozymandias" speaks of a ruined monument in the desert: "Round the decay/Of that colossal wreck, boundless and bare/The lone and level sands stretch far away". In fact, and just out of curosity, such a fascinating description fits very well the appearence of the Merurian Impact Crater named after him.

Date acquired: October, 17th, 2011
Image Mission Elapsed Time (MET): 227297821
Image ID: 894498
InstrumentNarrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 47,00° South
Center Longitude: 231,70° East
Solar Incidence Angle (at center frame): 67,6° (meaning that the Sun, at the time that the pictures were taken, was about 22,4° above the imaged Local Mercurian Horizon)
Emission Angle (at center frame): 25,9° (meaning that the Spacecraft was far away from being perpendicular to the imaged Surface at the time when the picture was taken)
Sun-Mercury-Messenger (or "Phase") Angle (at center frame): 73,2°

This picture (which is an Original NASA - MESSENGER Spacecraft's b/w and Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 18734) has been additionally processed, contrast enhanced, Gamma corrected, magnified to aid the visibility of the details and then re-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 Surface 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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