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Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Mercury
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The sky at

Mercury will reach half phase in its 2025 morning apparition. It will be shining brightly at mag 0.2.

From Cambridge , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 9° above the horizon at sunrise on 22 Apr 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 Cambridge local time.

Date Sun
sets at
rises at
at sunrise
at sunrise
01 Apr 202506:2805:49west
04 Apr 202506:2305:39west
07 Apr 202506:1805:30west
10 Apr 202506:1305:23west
13 Apr 202506:0805:16west
16 Apr 202506:0305:11north-west
19 Apr 202505:5805:06north-west
22 Apr 202505:5405:02north-west
25 Apr 202505:4904:59north-west
28 Apr 202505:4504:56north-west
01 May 202505:4104:53north-west
04 May 202505:3704:51north-west
07 May 202505:3304:49north-west
10 May 202505:3004:48north-west
13 May 202505:2704:48north-west
16 May 202505:2404:48north-west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2025 morning apparition of Mercury
24 Mar 2025 – Mercury at inferior solar conjunction
21 Apr 2025 – Mercury reaches highest point in morning sky
21 Apr 2025 – Mercury at greatest elongation west
24 Apr 2025 – Mercury at dichotomy
29 May 2025 – Mercury at superior solar conjunction

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 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 00h31m00s +00°23' Cetus 7.5"
Sun 02h08m +12°58' Aries 31'48"

The coordinates above are given in J2000.0.

The sky on 24 April 2025
Twilight ends
Twilight begins

26-day old moon
Waning Crescent


26 days old

Rise Culm. Set
Mercury 05:00 11:04 17:09
Venus 04:12 10:18 16:24
Moon 04:11 09:54 15:37
Mars 11:25 18:54 02:25
Jupiter 08:15 15:49 23:22
Saturn 04:33 10:25 16:17
All times shown in EDT.


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

24 Apr 2025  –  Mercury at dichotomy
29 May 2025  –  Mercury at superior solar conjunction
31 May 2025  –  Mercury at perihelion
27 Jun 2025  –  Mercury reaches highest point in evening sky

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