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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 evening 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 8° above the horizon at sunset on 15 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.

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
21 Sep 201918:5419:26west
24 Sep 201918:4919:23west
27 Sep 201918:4419:21west
30 Sep 201918:3819:18west
03 Oct 201918:3319:15south-west
06 Oct 201918:2819:12south-west
09 Oct 201918:2419:09south-west
12 Oct 201918:1919:06south-west
15 Oct 201918:1419:03south-west
18 Oct 201918:0919:00south-west
21 Oct 201918:0518:56south-west
24 Oct 201918:0018:52south-west
27 Oct 201917:5618:46south-west
30 Oct 201917:5218:39south-west
02 Nov 201917:4818:29south-west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 evening apparition of Mercury
19 Oct 2019 – Mercury reaches highest point 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

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 15h27m50s -22°01' 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 09:27 14:07 18:48
Venus 08:55 13:52 18:50
Moon 04:06 10:32 16:59
Mars 05:43 11:30 17:17
Jupiter 11:26 16:03 20:40
Saturn 13:03 17:42 22:21
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

25 Oct 2019  –  Mercury at dichotomy
11 Nov 2019  –  Mercury at inferior solar conjunction
11 Nov 2019  –  Transit of Mercury
16 Nov 2019  –  Mercury at perihelion

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