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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 2019 evening apparition. It will be shining brightly at mag 0.1.

From Fairfield , this apparition will be exceptionally well placed but tricky to observe, reaching a peak altitude of 18° above the horizon at sunset on 20 Jun 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 Fairfield local time.

Date Sun
sets at
sets at
at sunset
at sunset
27 May 201920:1320:48north-west
30 May 201920:1621:09north-west
02 Jun 201920:1821:2711°north-west
05 Jun 201920:2021:4213°west
08 Jun 201920:2221:5415°west
11 Jun 201920:2422:0316°west
14 Jun 201920:2622:0917°west
17 Jun 201920:2722:1118°west
20 Jun 201920:2822:1118°west
23 Jun 201920:2822:0817°west
26 Jun 201920:2922:0316°west
29 Jun 201920:2921:5615°west
02 Jul 201920:2921:4613°west
05 Jul 201920:2821:3411°west
08 Jul 201920:2721:20west
11 Jul 201920:2621:03west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 evening apparition of Mercury
17 Jun 2019 – Mercury at dichotomy
18 Jun 2019 – Mercury reaches highest point in evening sky
23 Jun 2019 – Mercury at greatest elongation east

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 07h29m50s +23°18' Gemini 7.3"
Sun 05h44m +23°23' Taurus 31'29"

The coordinates above are given in J2000.0.

The sky on 17 June 2019
Twilight ends
Twilight begins

14-day old moon
Waning Gibbous


14 days old

Rise Culm. Set
Mercury 07:06 14:39 22:11
Venus 04:23 11:46 19:09
Moon 20:58 00:45 05:30
Mars 07:10 14:41 22:12
Jupiter 19:39 00:23 05:02
Saturn 21:47 02:33 07:15
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

17 Jun 2019  –  Mercury at dichotomy
19 Jun 2019  –  Mercury reaches highest point in evening sky
23 Jun 2019  –  Mercury at greatest elongation east
07 Jul 2019  –  Mercury at aphelion

Image credit

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