Mercury's worsening apparition...or improving?

Event Date: March 16th

Time: 7:00 AM

Brief

   Today's subject header may seem misleading.  However, it depends from which latitude(s) in the world Mercury is being viewed from!

   Although it has separated quickly from our star, Mercury has also moved south of it very quickly.  Part of the reason of this is that the Sun is moving northbound at its fastest this week, nearly at the celestial equator, which it reaches on the 20th.  As for Mercury, it has also been a victim of the Sun's glare.  Taking a look below, is Mercury with its orbit and the celestial guidelines.  Notice how much more of the orbit's "loop" sticks above the horizon, compared to when it was at greatest elongation back in mid-February; a reminder of that can be found here.

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

Detailed

As it has separated from the Sun, Mercury has also moved closer to aphelion, which it will reach at the end of the month.  By then, the planet will be near greatest elongation and therefore, moving slightly away from us, while moving further from the Sun.  At that point, we will only see it at about dichotomy, Mercury will remain a dim magnitude for almost all of this time west of the Sun.

   As for this morning, Mercury rises 56 minutes before the Sun, and is already about 6 1/2º south of it.  That may not sound like much of a declination gap, yet it will grow quickly to almost double that during the few days of next month, during the week of aphelion.  The magnitude of Mercury will be almost opposite that of the greatest elongation in February: +0.3 instead of -0.3.  Once again, if that doesn't sound like a big difference, you are right.  However, considering that the February elongation had Mercury isolated in an astronomical-twilight sky about 4-6º above the horizon (exact mid-northern latitude depending), this time the planet will be nearly buried in the glare of a much more northern Sunrise in comparison.  If we combine the multiple factors of this worsening morning apparition of Mercury during March, one thing remains almost the same for about three weeks: the rise gap.  Considering that Mercury is separating from the Sun while becoming further south, that makes sense.

   In short, it is not a good showing of Mercury for much of the northern hemisphere.  For the southern hemisphere however, it is the best morning showing of Mercury this calendar year.  The planet rises over two hours before the Sun at and near the time of greatest elongation.