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Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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The sky at

Mercury will reach half phase in its 2020 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 10° above the horizon at sunrise on 10 Mar 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 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 Mar 202006:2105:41west
04 Mar 202006:1605:27west
07 Mar 202006:1105:15west
10 Mar 202007:0606:0610°west
13 Mar 202007:0105:5910°west
16 Mar 202006:5505:5410°west
19 Mar 202006:5005:5010°west
22 Mar 202006:4505:47west
25 Mar 202006:4005:44west
28 Mar 202006:3505:42west
31 Mar 202006:2905:40west
03 Apr 202006:2405:38west
06 Apr 202006:1905:37west
09 Apr 202006:1405:35west
12 Apr 202006:0905:34west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2020 morning apparition of Mercury
25 Feb 2020 – Mercury at inferior solar conjunction
18 Mar 2020 – Mercury reaches highest point in morning sky
22 Mar 2020 – Mercury at dichotomy
23 Mar 2020 – Mercury at greatest elongation west

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 22h26m10s -10°52' Aquarius 7.6"
Sun 00h07m +00°48' Pisces 32'05"

The coordinates above are given in J2000.0.

The sky on 22 March 2020
Twilight ends
Twilight begins

28-day old moon
Waning Crescent


28 days old

Rise Culm. Set
Mercury 05:47 11:10 16:33
Venus 08:21 15:42 23:03
Moon 06:26 11:48 17:10
Mars 03:51 08:27 13:04
Jupiter 03:43 08:22 13:01
Saturn 04:06 08:51 13:36
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

22 Mar 2020  –  Mercury at dichotomy
23 Mar 2020  –  Mercury at greatest elongation west
27 Mar 2020  –  Mercury at aphelion
04 May 2020  –  Mercury at superior solar conjunction

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