Mercury approaches perihelion, north of Sun

Event Date: January 27th

Time: 5:30 PM

Brief

   We previewed Mercury's trek east of the Sun last week, while it was still a couple of degrees south of our star as a result, setting first, among the two.  Now, Mercury still isn't separated enough from the Sun to be unaided-eye visible, yet by next week, that could change.  If you are viewing with an unobstructed horizon, preferably high enough up to see over most or all obstructions such as tall trees and buildings, try to find it.  Mercury sets 28 minutes after the Sun this evening.  Here it is with the setting Sun below, with Mercury's orbit showing.  Note where it is related to the ecliptic, in latitude.

click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

   Look where the ecliptic crosses the celestial equator, not far east of Mercury.  Because of this, where the next several degrees that Mercury will move in longitude will have it increase in declination.  As it does, approaching perihelion in mid-February and separating from the Sun, the few days before greatest elongation will have Mercury displayed as easiest to see with the eyes.  After all, with the Sun moving a little further north each day and Mercury slowly dimming as it wanes, we want to get the best view of it displayed in a dark enough skies.  The combination of it bright and twilight ending soon enough, will give us the chance to see it with the eye early.  As a good test, try timing how long you need to wait between official Sunset time and when you first see the planet with the eye...even as a very faint dot in challenging twilight.  Right now at magnitude -1.2, this doesn't seem like the most spectacular magnitude for Mercury, yet just wait: as it approaches perihelion, the dimming will once again, be slow.  Combining that with an improving emergence from the Sun over the next two weeks, we are in for an elusive planet treat.