Tuesday December 29th Mercury, the innermost planet, will reach its orbital position known as greatest eastern elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
From our perspective Mercury, and Venus for that matter, appear to move out to the left (east) from the Sun for a period, then reverse and move westward between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
Mercury is currently visible as an ‘evening star’ over the western horizon at sunset. Further to the east and higher above the horizon is the dwarf planet Ceres and the outermost planet Neptune. Both are dim and are just beyond the light grasp of the naked eye but could be seen through binoculars as a star-like point of light.
If your viewing is done with a telescope then keep a close eye, or eyepiece, on Ceres as over a several day period, December 29th to January 2nd Ceres will be moving past M-30, a globular star cluster (fuzzy blur on left edge of field of view). This is a simulated view through a 25mm eyepiece on an 8″ Reflector.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.