Mercury Setting
Taken by Helio C. Vital on April 17, 2016 @
Rio de Janeiro, Brazil
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Details:
Mercury will reach its greatest eastern elongation tomorrow. However, observers in mid-southern latitudes are still having a tough time trying to spot it in the evening twilight as the planet is barely reaching naked-eye visibility. The reason for that is the current shallow angle between the ecliptic and the horizon at the sunset point (some 45°) that has kept Mercury very low in the west, where the contrast between its image (dimmed by severe atmospheric extinction - over 10 air masses) and the bright sky background is quite poor. Let us consider the circumstances for tomorrow as an example. When the Sun sets, the elusive little planet will be only 11.1° above Rio`s west-northwestern horizon in spite of its considerable 19.9° elongation. However, the use of a high zoom camera can help in the case. See the animation I made this evening. It includes a total of 24 photos, taken about 38 minutes after sunset (21:14 - 21:19 UT) and shows Mercury setting behind a hill 5 km away. The photos were taken with a Sony Cyber-Shot HX300 camera. The corresponding ranges for the elevation and azimuth of the planet along its recorded path were 3.7° - 2.7° and 293.6° - 291.7°, respectively, while the Sun was roughly 10° below the horizon.
Photographer's website:
http://https://www.flickr.com/photos/98669508@N03/
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