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Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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Mercury will reach half phase in its 2025 morning apparition. It will be shining brightly at mag -0.4.

From Fairfield , this apparition will be well placed but tricky to observe, reaching a peak altitude of 16° above the horizon at sunrise on 20 Aug 2025.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

The table below lists how high Mercury will appear at sunrise over the course of the apparition. All times are given in Fairfield local time.

Date Sun
sets at
rises at
at sunrise
at sunrise
08 Aug 202505:5705:06north-west
11 Aug 202506:0004:5012°north-west
14 Aug 202506:0304:3914°north-west
17 Aug 202506:0604:3415°north-west
20 Aug 202506:0904:3416°north-west
23 Aug 202506:1204:3916°north-west
26 Aug 202506:1504:4914°north-west
29 Aug 202506:1805:0312°north-west
01 Sep 202506:2105:1910°west
04 Sep 202506:2405:36west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2025 morning apparition of Mercury
31 Jul 2025 – Mercury at inferior solar conjunction
19 Aug 2025 – Mercury reaches highest point in morning sky
19 Aug 2025 – Mercury at greatest elongation west
21 Aug 2025 – Mercury at dichotomy

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 days 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 hours, 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 08h48m50s +17°26' Cancer 7.0"
Sun 10h01m +12°04' Leo 31'37"

The coordinates above are given in J2000.0.

The sky on 21 August 2025
Twilight ends
Twilight begins

28-day old moon
Waning Crescent


28 days old

Rise Culm. Set
Mercury 04:35 11:42 18:49
Venus 03:18 10:38 17:59
Moon 04:17 11:40 19:04
Mars 09:33 15:25 21:17
Jupiter 02:31 10:00 17:28
Saturn 20:59 02:58 08:54
All times shown in EDT.


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.


The circumstances of this event were computed using the DE405 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

19 Aug 2025  –  Mercury reaches highest point in morning sky
29 Oct 2025  –  Mercury at greatest elongation east
01 Nov 2025  –  Mercury reaches highest point in evening sky
08 Dec 2025  –  Mercury reaches highest point in morning sky

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