Neptune and 136199 Eris will share the same right ascension, with Neptune passing 6°43' to the north of 136199 Eris.
From South El Monte , the pair will be visible in the dawn sky, rising at 01:57 (PST) – 3 hours and 44 minutes before the Sun – and reaching an altitude of 30° above the eastern horizon before fading from view as dawn breaks at around 04:29.
Neptune will be at mag 7.9, and 136199 Eris at mag 18.6, both in the constellation Pisces.
A graph of the angular separation between Neptune 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 |
| Neptune | 01h56m00s | 10°03'N | Pisces | 7.9 | 2"2 |
| 136199 Eris | 01h56m00s | 3°20'N | Pisces | 18.6 | 0"0 |
The coordinates above are given in J2000.0. The pair will be at an angular separation of 68° from the Sun, which is in Gemini at this time of year.
The sky on 20 Dec 2025
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All times shown in PST.
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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.