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Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Mercury
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Mercury will reach half phase in its 2020 evening apparition. It will be shining brightly at mag -0.1.

From Ashburn , this apparition will be exceptionally well placed but tricky to observe, reaching a peak altitude of 19° above the horizon at sunset on 29 May 2020.

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 sunset over the course of the apparition. All times are given in Ashburn local time.

Date Sun
sets at
sets at
at sunset
at sunset
11 May 202020:1220:54west
14 May 202020:1521:1511°west
17 May 202020:1721:3413°west
20 May 202020:2021:5015°west
23 May 202020:2222:0317°west
26 May 202020:2522:1318°west
29 May 202020:2722:1919°west
01 Jun 202020:2922:2219°west
04 Jun 202020:3122:2219°west
07 Jun 202020:3322:1818°west
10 Jun 202020:3422:1217°west
13 Jun 202020:3622:0215°west
16 Jun 202020:3721:4912°west
19 Jun 202020:3821:34west
22 Jun 202020:3821:16west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2020 evening apparition of Mercury
04 May 2020 – Mercury at superior solar conjunction
29 May 2020 – Mercury at dichotomy
03 Jun 2020 – Mercury reaches highest point in evening sky
04 Jun 2020 – Mercury at greatest elongation east

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 06h04m20s +25°34' Gemini 7.2"
Sun 04h27m +21°43' Taurus 31'33"

The coordinates above are given in J2000.0.

The sky on 29 May 2020
Twilight ends
Twilight begins

7-day old moon
Waxing Crescent


7 days old

Rise Culm. Set
Mercury 07:10 14:44 22:19
Venus 06:10 13:40 21:10
Moon 12:29 19:19 01:32
Mars 02:02 07:33 13:04
Jupiter 23:41 04:36 09:27
Saturn 23:57 04:56 09:51
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

29 May 2020  –  Mercury at dichotomy
03 Jun 2020  –  Mercury reaches highest point in evening sky
04 Jun 2020  –  Mercury at greatest elongation east
22 Jun 2020  –  Mercury at aphelion

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