Mercury and 136199 Eris will share the same right ascension, with Mercury passing 6°26' to the north of 136199 Eris.
From South El Monte however, the pair will not be readily observable since they will be very close to the Sun, at a separation of only 17° from it.
Mercury will be at mag -0.9, and 136199 Eris at mag 18.6, both in the constellation Pisces.
A graph of the angular separation between Mercury and 136199 Eris 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 |
| Mercury | 01h54m50s | 9°54'N | Pisces | -0.9 | 5"3 |
| 136199 Eris | 01h54m50s | 3°28'N | Pisces | 18.6 | 0"0 |
The coordinates above are given in J2000.0. The pair will be at an angular separation of 13° from the Sun, which is in Aries at this time of year.
The sky on 21 Dec 2025
| The sky on 21 December 2025 | ||||||||||||||||||||||||||||||||||
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5% 2 days old |
All times shown in PST.
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Warning
Never attempt to point a pair of binoculars or a telescope at an object close to the Sun. Doing so may result in immediate and permanent blindness.
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.