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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 2019 evening apparition. It will be shining brightly at mag -0.6.

From Washington , this apparition will be well placed but tricky to observe, reaching a peak altitude of 18° above the horizon at sunset on 27 Feb 2019.

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 Washington local time.

Date Sun
sets at
sets at
at sunset
at sunset
09 Feb 201918:0518:41south-west
12 Feb 201918:0818:5710°west
15 Feb 201918:1119:1212°west
18 Feb 201918:1419:2614°west
21 Feb 201918:1819:3916°west
24 Feb 201918:2119:4817°west
27 Feb 201918:2419:5318°west
02 Mar 201918:2719:5216°west
05 Mar 201918:2919:4415°west
08 Mar 201918:3219:2911°west
11 Mar 201919:3520:08west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 evening apparition of Mercury
29 Jan 2019 – Mercury at superior solar conjunction
26 Feb 2019 – Mercury at dichotomy
26 Feb 2019 – Mercury at greatest elongation east
01 Mar 2019 – Mercury reaches highest point in evening sky

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 23h41m30s -00°28' Pisces 7.1"
Sun 22h36m -08°45' Aquarius 32'18"

The coordinates above are given in J2000.0.

The sky on 26 February 2019
Twilight ends
Twilight begins

22-day old moon
Waning Crescent


22 days old

Rise Culm. Set
Mercury 07:49 13:50 19:52
Venus 05:01 10:01 15:00
Moon 01:31 06:38 11:45
Mars 09:41 16:30 23:19
Jupiter 02:41 07:31 12:21
Saturn 04:31 09:23 14:16
All times shown in MST.


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

15 Dec 2018  –  Mercury at greatest elongation west
26 Feb 2019  –  Mercury at greatest elongation east
01 Mar 2019  –  Mercury reaches highest point in evening sky
09 Apr 2019  –  Mercury reaches highest point in morning sky

Image credit

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