Mercury joins Venus and Jupiter in east

Event Date: August 3rd
Time: 6:00 AM


Brief

   Shortly before Mercury reached inferior conjunction in late July, it reached perihelion.  Unfortunately, its retrograde motion had brought it too close to the Sun to see.  Even if it was far enough from the Sun to try to view, it would have been very dim, and the geometry of the western evening sky was becoming worse each day.  Now, as we start August looking towards the east in the morning, the geometry is improving at that azimuth.  Here is the elusive planet shown in orbit for this morning.  Notice that we are looking far from edge-on to the plane, north of it.  Therefore, Mercury's ecliptic latitude of (-)4.3º south, coupled with moving a bit further from the Sun towards aphelion over the next month, will slightly slow down its rate of brightening.

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

Detailed

   Mercury's current retrograde motion is pulling it quickly from the Sun, and will gradually brighten, to become more visible.  By the middle and end of August, we will have Mercury at its best apparition since that bright greatest-elongation sighting in March.  At that time, it was far enough north of the Sun looking west.  Approximately half a year later, as hinted above, the geometry quality reverses for the time of day.  As a result, Mercury will become more and more north of the Sun, until it speeds up enough in prograde motion to fall back into the glare of the Sun.  Since our star is now rising later, faster, than it was during mid-June and July, that will give us a darker sky each week while Mercury brightens.
   Mercury is only magnitude +3.3 this morning and not visible with the Sun rising shortly after.  In about three weeks, after greatest elongation, Mercury improves in apparition for one more week before the declination gap between it and the Sun starts to shrink.  By then, it will be an easy target to view, below (unlabeled) Venus and Jupiter higher in the southeast.  Because the greatest elongation will be less than 19º, as opposed to 28º at best for some times of the year, the maximum gap between Sunrises will only reach 90 minutes.  Still, this will be enough time to easily see Mercury...especially as it brightens after that.  Look forward to a good pairing with the waning crescent Moon by mid-August, and I will talk more about that when we reach those dates.