Jupiter and Mercury will share the same right ascension, with Jupiter passing 52' to the south of Mercury.
From Cambridge , the pair will be difficult to observe as they will appear no higher than 9° above the horizon. They will be visible in the dawn sky, rising at 05:34 (EDT) – 1 hour and 34 minutes before the Sun – and reaching an altitude of 9° above the south-eastern horizon before fading from view as dawn breaks at around 06:42.
Jupiter will be at mag -1.8, and Mercury at mag -0.5, both in the constellation Ophiuchus.
The pair will be a little too widely separated to fit comfortably within the field of view of a telescope, but will be visible to the naked eye or through a pair of binoculars.
A graph of the angular separation between Jupiter and Mercury around the time of closest approach is available here.
The positions of the two objects at the moment of conjunction will be as follows:
| Object | Right Ascension | Declination | Constellation | Magnitude | Angular Size |
| Jupiter | 16h30m40s | 21°12'S | Ophiuchus | -1.8 | 30"7 |
| Mercury | 16h30m40s | 20°20'S | Ophiuchus | -0.5 | 5"9 |
The coordinates above are given in J2000.0. The pair will be at an angular separation of 20° from the Sun, which is in Sagittarius at this time of year.
The sky on 21 Dec 2018
| The sky on 21 December 2018 | ||||||||||||||||||||||||||||||||||
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99% 14 days old |
All times shown in EST.
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Source
The circumstances of this event were computed using the DE430 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.
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Image credit
The Moon in conjunction with Venus and Jupiter, with the Very Large Telescope in the foreground. Image © Y. Beletsky, ESO, 2009.