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A R C H I V E S

Today's APOD is (once again) an image of the Jovian moon Europa that was taken by the NASA - Galileo Spacecraft under the so-called "Low-Sun Conditions" (meaning that the picture was taken in such a way and manner that the Illumination Geometry of the photographed portion of the Surface was fit to show, in an enhanced and emphasized way, the exact Topography of the Terrain that was being pictured; this result can only be obtained when each and every Surface Relief is projecting, at the time that the picture is taken, its longest shadow and this means that the very best moment to do so is when the Spacecraft is flying over a Region where either the Sunrise, or the Sunset are occurring). However, we have to duly note and underline that, in this specific image, the Topography of the Terrain has been digitally emphasized.

In fact, Planetary Geologists can use the information obtained from images acquired under a variety of Illumination's Geometries (---> Lighting Conditions) not only to identify different types of Surface Features, but also to interpret the way that they could have formed and, last but not least, to measure their heights (remember, for example, that the length of the shadow cast by any given Surface Feature, like a Ridge or a Knob, once the Solar Incidence Angle (S.I.A.) is known, can be used to calculate the height of the Feature itself). The measurements - obtained from shadow lengths - relevant to the Surface Features visible in this frame, indicate that they range from an height of only a few tens (such as 20/25), up to - approximately - 100 meters. The NASA - Galileo Spacecraft acquired this image of the Surface of Europa during its 3rd (third) orbit around Jupiter. The whole image, which is centered at about 10° South Lat. and 190° West Long., covers an area of approx. 75 by 40 Km (such as about 45 by 25 miles).

This frame has been colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Galileo Spacecraft and then looked down, towards the Surface of the Jovian moon Europa), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.