Event Date: October 25th
Time: 6:30 PM
Brief
Mercury is almost at greatest elongation, setting a maximum 57 minutes after the Sun for the next few days. It is still a decent apparition for being so far along in this swing east of the Sun, at -0.1. To put this in perspective, the star Vega is just slightly dimmer, at magnitude 0.0. Of course, Vega is high and far out of the glare of the Sun right now, making it easier to see first before Mercury. Also, Mercury is buried in atmospheric pollution once finally visible with the eye alone. At a separation of 24º, Mercury is just short of 7º in altitude at the time above, being the middle of civil twilight.
The image shows Mercury and its orbit, along with the celestial guidelines, looking west-southwest.
Detailed
Although Mercury is still south of the ecliptic and seen low, it will very slightly improve in apparition over the next few days. The geometry of the western evening sky also has improved since late August. Unfortunately, we lose Mercury to the glare of the Sun and then inferior conjunction, yet will have it for a much better apparition during the last month of the season. Until then, the Sun continues to move south and therefore, darkness comes quickly with a shorter twilight time than we have on average at about the time of the equinoxes.
This second image shows the elusive planet at more than half-illuminated (dichotomy), yet nearing it, which is often the case before time of greatest elongation. The planet will wane faster between dichotomy and old-crescent fast, although through a powerful enough telescope with a small field, we will see the angular size of the planet grow. Although low to the horizon, I will magnify the planet to about 200x. The current percentage illuminated is 64%. Look very closely, and even if looking small (6.5 arc-seconds), you may notice that slight gibbous curve.
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click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.
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