Astronomy Picture of the Day
April 29, 2013

High Latitude, Low Sun
High Latitude, Low Sun

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.

Today's APOD shows you the first set of Absolute Natural Color images taken from a new Imaging Campaign: the so-called "Minimum-Phase-Angle Color". In fact, near the North Polar Regions of Mercury, the Solar Incidence Angle is always quite high because the Sun is always very low on the imaged Local Horizon. The Minimum-Phase-Angle Color Campaign acquires images from as close to the direction of Solar Illumination as possible: a circumstance, this one, which minimizes the Phase Angle and therefore also the Shadows that are present in a certain, given area. The images are acquired through 5 (five) of the WAC's Narrow-Band Color Filters, for those Mercurian Regions whose Latitude is equal or higher than 60° North, at an average Resolution of 500 meters/pixel. 

With this Minimum-Phase-Angle Color Campaign, the MESSENGER Team will be searching for Spectral Differences among Mercury's Northern Smooth Plains and the Ejecta Blankets of the Impact Craters located inside them. Remember that the existence of a Spectral Difference indicates the presence of a Mineralogical (---> Compositional) difference in the Material/s forming the aforementioned Plains and Ejecta Blankets. In this image-mosaic you can see a portion of Botticelli Crater (approx. 120 Km - or 74,52 miles - in diameter), which does not appear to have a strong color contrast from its surroundings.

Date acquired: March, 21st, 2013
Images Mission Elapsed Time (MET): 6148727, 6148718, 6148724
Images ID: 3731063, 3731060, 3731062
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 62,14° North
Center Longitude: 248,10° East
Resolution: 316 meters/pixel
Solar Incidence Angle: 77,3° (meaning that the Sun, at the time that the picture was taken, was about 12,7° above the imaged Local Mercurian Horizon)
Emission Angle: 49,2°
Sun-Mercury-Messenger (or "Phase") Angle: 28,0°

This image (which is an Original NASA - MESSENGER Spacecraft Map Projected false color image-mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 16906) has been additionally processed 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 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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