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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 2019 morning apparition. It will be shining brightly at mag -0.4.

From Ashburn , this apparition will be exceptionally well placed but tricky to observe, reaching a peak altitude of 17° above the horizon at sunrise on 28 Nov 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 sunrise over the course of the apparition. All times are given in Ashburn local time.

Date Sun
rises at
rises at
at sunrise
at sunrise
16 Nov 201906:5605:5610°south-east
19 Nov 201907:0005:3614°south-east
22 Nov 201907:0305:2617°south-east
25 Nov 201907:0605:2317°south-east
28 Nov 201907:0905:2517°south-east
01 Dec 201907:1205:3117°south-east
04 Dec 201907:1505:3915°south-east
07 Dec 201907:1805:4814°south-east
10 Dec 201907:2005:5913°south-east
13 Dec 201907:2306:0911°south-east
16 Dec 201907:2506:2110°south-east
19 Dec 201907:2706:32south-east
22 Dec 201907:2806:43south-east
25 Dec 201907:2906:53south-east

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 morning apparition of Mercury
25 Nov 2019 – Mercury at dichotomy
27 Nov 2019 – Mercury reaches highest point in morning sky
28 Nov 2019 – 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 14h45m30s -13°23' Libra 7.2"
Sun 16h02m -20°40' Scorpius 32'24"

The coordinates above are given in J2000.0.

The sky on 25 November 2019
Twilight ends
Twilight begins

28-day old moon
Waning Crescent


28 days old

Rise Culm. Set
Mercury 05:21 10:40 15:58
Venus 09:15 13:50 18:26
Moon 05:51 11:08 16:26
Mars 04:38 10:01 15:24
Jupiter 09:03 13:45 18:27
Saturn 10:21 15:07 19:53
All times shown in EST.


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

25 Nov 2019  –  Mercury at dichotomy
27 Nov 2019  –  Mercury reaches highest point in morning sky
28 Nov 2019  –  Mercury at greatest elongation west
30 Dec 2019  –  Mercury at aphelion

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