Mercury emerging west of Sun: dim and low

Event Date: March 8th

Time: 6:00 AM

Brief

   We just saw Mercury have its best evening apparition of the year, regarding declination difference with the Sun.  Mercury was a wonderful sight to see the few days before both greatest elongation and perihelion.  Now, as it slows down in retrograde on the west side of the Sun, Mercury is starting its poorest morning apparition of the year.  It only gets worse as the planet stays on this side of the Sun, between now and the days after greatest elongation.  I will explain more about that in the detailed section, following this image of Mercury with the celestial equator, ecliptic, and its orbit.

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

Detailed

   The first thing to take note of is Mercury's ecliptic latitude: we are viewing its plane from an angle, which lets us see it over 3º north.  It was because of this good latitude, that during its previous apparition in the evening, the ecliptic didn't have to have the best angle with the horizon.  Now, as Mercury swings back towards the other side of the Sun, it will stay there--from our perspective--for a little over the course of a little over two months.  The planet reaches aphelion in a little over a month from now, which is about the time of its next greatest elongation.  As it approaches that point, retrograde has already ended, yet not before the planet falls far enough south of the Sun to be in the glare of it for most of this apparition.  

   Of course, most southern hemisphere viewers will love this apparition.  For them, Mercury will not only be about as far separated as it will be all year; with favorable geometry, certain latitudes there see the planet set a little over 2 hours after Sunset, and well out of the atmospheric pollution.  As for us, with unfavorable geometry and a Sun rising over a minute earlier each morning between now and about late April, we are best off seeing Mercury for its next morning apparition, when the declination is about the same during the days sandwiching that of greatest elongation.  Until that time, try to find Mercury in a few weeks with optical aid, and with the eye a couple weeks after that.