© NASA/JPL/MESSENGER

Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Mercury
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Mercury will reach half phase in its Nov 2025–Jan 2026 morning apparition. It will be shining brightly at mag -0.4.

From San Diego , this apparition will be well placed but tricky to observe, reaching a peak altitude of 18° above the horizon at sunrise on 7 Dec 2025.

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Nov 2025–Jan 2026 morning apparition of Mercury

20 Nov 2025 – Mercury at inferior solar conjunction
04 Dec 2025 – Mercury at dichotomy
05 Dec 2025 – Mercury at highest altitude in morning sky
07 Dec 2025 – Mercury at greatest elongation west

The table below lists the altitude of Mercury at sunrise over the course of the apparition. All times are given in San Diego local time.

Date Sun
rises at
Mercury
rises at
Altitude
at sunrise
Direction
at sunrise
Mag Phase
24 Nov 202506:2405:39south-east2.87%
27 Nov 202506:2705:1613°south-east1.119%
30 Nov 202506:2905:0116°south-east0.133%
03 Dec 202506:3204:5418°south-east-0.346%
06 Dec 202506:3404:5318°south-east-0.557%
09 Dec 202506:3704:5618°south-east-0.567%
12 Dec 202506:3905:0117°south-east-0.574%
15 Dec 202506:4105:0816°south-east-0.579%
18 Dec 202506:4305:1715°south-east-0.584%
21 Dec 202506:4405:2613°south-east-0.587%
24 Dec 202506:4605:3512°south-east-0.590%
27 Dec 202506:4705:4510°south-east-0.592%
30 Dec 202506:4805:54south-east-0.594%
02 Jan 202606:4806:04south-east-0.696%
05 Jan 202606:4906:13south-east-0.797%

Mercury will brighten rapidly at the start of its morning apparition as it emerges from inferior conjunction. Prior to its apparition, it passed between the Earth and Sun, at which time it had its unilluminated side turned towards the Earth and so appeared as a thin, barely illuminated crescent. As the apparition proceeds, this crescent waxes and becomes gibbous.

Since Mercury can only ever be observed in twilight, it is particularly difficult to find when it is in a thin crescent phase. Thus, it will be significantly easier to see in the days after it reaches its highest point in the sky – when it will show a gibbous phase – than in the days beforehand.

Altitude of Mercury at sunrise

A graph of the phase of Mercury is available here.

Apparitions of Mercury

03 Jul 2025 – Evening apparition
19 Aug 2025 – Morning apparition
29 Oct 2025 – Evening apparition
07 Dec 2025 – Morning apparition
19 Feb 2026 – Evening apparition
03 Apr 2026 – Morning apparition
15 Jun 2026 – Evening apparition

Observing Mercury

Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is lost in the Sun's glare much of the time.

It is observable for only a few weeks each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions repeat roughly once every 3–4 months.

Mercury's phase

Mercury's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon.

Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times.

Mercury shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few days, only because Mercury's orbit is not quite perfectly aligned with the ecliptic.

Mercury's position

The coordinates of Mercury when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Mercury 15h21m10s 15°47'S Libra 7.3"
Sun 16h42m 22°13'S Ophiuchus 32'27"

The coordinates above are given in J2000.0.

The sky on 4 Dec 2025

The sky on 4 December 2025
Sunrise
06:33
Sunset
16:41
Twilight ends
18:09
Twilight begins
05:05

14-day old moon
Waxing Gibbous

99%

14 days old

Planets
Rise Culm. Set
Mercury 04:55 10:15 15:36
Venus 05:57 11:04 16:11
Moon 16:19 23:57 07:39
Mars 07:20 12:17 17:14
Jupiter 19:36 02:37 09:39
Saturn 12:44 18:36 00:28
All times shown in PST.

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.

Related news

31 Oct 2025  –  Mercury at highest altitude in evening sky
06 Dec 2025  –  Mercury at highest altitude in morning sky
07 Dec 2025  –  Mercury at greatest elongation west
19 Feb 2026  –  Mercury at greatest elongation east

Image credit

© NASA/JPL/MESSENGER

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