Mercury sinking towards Sun; Venus not far behind

Event Date: December 28th

Time: 7:00 AM

Brief

  As Mercury has started to move faster in prograde motion over the last few weeks since shortly before greatest elongation, it has started to catch up with the Sun faster.  As a result, despite still a good magnitude of -0.6, we are losing it quickly to morning twilight.  As for its planetary neighbor Venus, it has also increased in prograde motion.  However, with a much larger orbit than Mercury, being further from the Sun, the two have become more separated every day since their closest encounter earlier this month.  Here they are, pictured with orbits, ecliptic, and celestial equator.

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

Detailed

   While still visible to the eye alone through atmospheric pollution, Mercury is shortly lost in the Sun's glare by early into the new [calendar] year.  We are just days away from losing it entirely until late January, when it begins a very good evening apparition, once again going north of the Sun.  We will show that enough when the time comes.  

   As the ecliptic shows above, the two planets are about the same ecliptic latitude, yet more importantly, about the same declination as the Sun.  As the next few weeks pass, the geometry of this [east] side of the morning sky worsens more and more quickly.  Therefore, along with the Sun moving towards the celestial equator again, they will be seen for less time in dark-enough sky after rising.  Of course, approaching superior conjunction will also lead to them quickly disappearing in the Sun's glare.  Mercury rises 48 minutes before the Sun this morning, yet only 44 minutes before it tomorrow.  Venus rises 98 minutes before the Sun this morning, and this decreases by two minutes tomorrow.  I am including tomorrow's intervals just to show how quickly each are shrinking with change in declination.