Mars and Neptune will share the same right ascension, with Mars passing 2°38' to the south of Neptune.
From South El Monte however, the pair will not be observable – they will reach their highest point in the sky during daytime and will be no higher than 20° above the horizon at dusk.
Mars will be at mag 1.0, and Neptune at mag 8.0, both in the constellation Ophiuchus.
The pair will be too widely separated to fit within the field of view of a telescope, but will be visible through a pair of binoculars.
A graph of the angular separation between Mars and Neptune 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 |
| Mars | 17h39m00s | 24°45'S | Ophiuchus | 1.0 | 5"3 |
| Neptune | 17h39m00s | 22°07'S | Ophiuchus | 8.0 | 2"2 |
The coordinates above are given in J2000.0. The pair will be at an angular separation of 53° from the Sun, which is in Virgo at this time of year.
The sky on 12 Sep 2025
| The sky on 12 September 2025 | ||||||||||||||||||||||||||||||||||
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67% 20 days old |
All times shown in PDT.
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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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| 05 Sep 1982 | – Neptune ends retrograde motion |
| 31 Mar 1983 | – Neptune enters retrograde motion |
| 19 Jun 1983 | – Neptune at opposition |
| 08 Sep 1983 | – Neptune ends retrograde motion |
Image credit
The Moon in conjunction with Venus and Jupiter, with the Very Large Telescope in the foreground. Image © Y. Beletsky, ESO, 2009.