Event Date: February 21st
Time: 6:15 PM
Brief
Although Mercury maintains a good apparition during this week past greatest eastern elongation, (g.e.e.), it is already dimming quickly. Take a look below, as I show it with orbit, as well as the celestial equator and ecliptic. Mars, which Mercury has been in binocular view with over the last couple of weeks, is labeled too, yet getting much harder to see each day even through a telescope; it sinks gradually towards the Sun. The second image shows Mercury magnified and showing the crescent shape. The field of view for that one is 1/10º and therefore, a magnification of about 500x. I do this to make Mercury more visible, yet realistically with atmospheric pollution, 200-250x is more ideal.
 |
click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.
|
Detailed
At magnitude +0.6, Mercury is starting to catch up with Mars (+1.2) in magnitude, a little over 5º away from it. The main reason for Mercury dimming quickly is simple: it it is waning quickly, and much moreso than it is increasing in lit surface area. At 26% illuminated, that is about half of what Mercury was was at g.e.e. Since then, it as only increased in angular size by a little more than one arc-second. When looking at it through optical aid this evening and over the next few, wanes further to a sliver, starts retrograde motion, and disappears into the glare of the Sun quickly. Therefore, try to catch it tonight-- especially since it is still a good altitude. It takes about 30=40 minutes to see it easily with the eye, yet it can be picked up with a telescope shortly after Sunset if you know where to look. As Mercury's ecliptic latitude increases while the geometry of this part of this sky also improves, it is far enough north of the Sun that it is almost directly above it azimuth-wise. Four evenings from now on the 25th, as a very thin crescent, it will be the same azimuth as the Sun, yet very dim and hard to find by then.
No comments:
Post a Comment