Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Mercury
Please wait
Loading 0/4
Click and drag to rotate
Mouse wheel to zoom in/out
Touch with mouse to dismiss
The sky at

Mercury will reach half phase in its Oct 2019 evening apparition. It will be shining brightly at mag -0.1.

From Seattle , this apparition will be unobservable, reaching a peak altitude of 4° above the horizon at sunset on 19 Oct 2019.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

Oct 2019 evening apparition of Mercury

14 Oct 2019 – Mercury at highest altitude in evening sky
19 Oct 2019 – Mercury at greatest elongation east
25 Oct 2019 – Mercury at dichotomy
11 Nov 2019 – Mercury at inferior solar conjunction

A graph of the phase of Mercury is available here.

Apparitions of Mercury

11 Apr 2019 – Morning apparition
23 Jun 2019 – Evening apparition
09 Aug 2019 – Morning apparition
19 Oct 2019 – Evening apparition
28 Nov 2019 – Morning apparition
10 Feb 2020 – Evening apparition
23 Mar 2020 – Morning apparition

Observing Mercury

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 days, 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 15h27m50s 22°01'S Libra 7.4"
Sun 13h57m -11°59' Virgo 32'09"

The coordinates above are given in J2000.0.

The sky on 25 October 2019
Twilight ends
Twilight begins

27-day old moon
Waning Crescent


27 days old

Rise Culm. Set
Mercury 10:03 14:22 18:40
Venus 09:27 14:07 18:47
Moon 04:09 10:54 17:25
Mars 06:02 11:45 17:28
Jupiter 12:04 16:17 20:31
Saturn 13:40 17:56 22:13
All times shown in PDT.


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

19 Oct 2019  –  Mercury at greatest elongation east
11 Nov 2019  –  Transit of Mercury
26 Nov 2019  –  Mercury at highest altitude in morning sky
28 Nov 2019  –  Mercury at greatest elongation west

Image credit







Color scheme