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 2021 morning apparition. It will be shining brightly at mag 0.1.

From Fairfield , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 11° above the horizon at sunrise on 23 Feb 2021.

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
rises at
rises at
at sunrise
at sunrise
11 Feb 202106:5406:16east
14 Feb 202106:5005:58south-east
17 Feb 202106:4605:4410°south-east
20 Feb 202106:4205:3311°south-east
23 Feb 202106:3805:2611°south-east
26 Feb 202106:3305:2111°south-east
01 Mar 202106:2905:1811°south-east
04 Mar 202106:2405:1611°south-east
07 Mar 202106:1905:1510°south-east
10 Mar 202106:1405:1510°south-east
13 Mar 202106:0905:14south-east
16 Mar 202107:0406:14south-east
19 Mar 202106:5906:13east
22 Mar 202106:5406:13east
25 Mar 202106:4906:13east
28 Mar 202106:4406:12east

A graph of the phase of Mercury is available here.

Observing Mercury

The 2021 morning apparition of Mercury
08 Feb 2021 – Mercury at inferior solar conjunction
28 Feb 2021 – Mercury reaches highest point in morning sky
02 Mar 2021 – Mercury at dichotomy
06 Mar 2021 – 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 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 21h09m40s -16°07' Capricornus 7.6"
Sun 22h53m -07°05' Aquarius 32'16"

The coordinates above are given in J2000.0.

The sky on 02 March 2021
Twilight ends
Twilight begins

19-day old moon
Waning Gibbous


19 days old

Rise Culm. Set
Mercury 05:16 10:21 15:26
Venus 06:19 11:45 17:10
Moon 22:04 02:39 08:27
Mars 09:33 16:56 00:20
Jupiter 05:25 10:29 15:32
Saturn 05:00 09:55 14:50
All times shown in EST.


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

02 Mar 2021  –  Mercury at dichotomy
06 Mar 2021  –  Mercury at greatest elongation west
13 Mar 2021  –  Mercury at aphelion
18 Apr 2021  –  Mercury at superior solar conjunction

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