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

From Cambridge , this apparition will be well placed but tricky to observe, reaching a peak altitude of 16° above the horizon at sunrise on 12 Aug 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 Cambridge local time.

Date Sun
rises at
rises at
at sunrise
at sunrise
28 Jul 201905:3405:00east
31 Jul 201905:3704:43east
03 Aug 201905:4004:2911°east
06 Aug 201905:4304:2014°east
09 Aug 201905:4704:1515°east
12 Aug 201905:5004:1616°east
15 Aug 201905:5304:2115°east
18 Aug 201905:5604:3114°east
21 Aug 201905:5904:4512°east
24 Aug 201906:0205:0110°east
27 Aug 201906:0605:20east

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 morning apparition of Mercury
21 Jul 2019 – Mercury at inferior solar conjunction
09 Aug 2019 – Mercury at greatest elongation west
10 Aug 2019 – Mercury reaches highest point in morning sky
12 Aug 2019 – Mercury at dichotomy

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 08h10m30s +19°18' Cancer 7.0"
Sun 09h26m +15°01' Leo 31'33"

The coordinates above are given in J2000.0.

The sky on 12 August 2019
Twilight ends
Twilight begins

11-day old moon
Waxing Gibbous


11 days old

Rise Culm. Set
Mercury 04:15 11:33 18:51
Venus 05:44 12:49 19:54
Moon 18:24 23:01 02:46
Mars 06:22 13:17 20:12
Jupiter 15:36 20:12 00:53
Saturn 17:48 22:24 03:03
All times shown in EDT.


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 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

12 Aug 2019  –  Mercury at dichotomy
20 Aug 2019  –  Mercury at perihelion
03 Sep 2019  –  Mercury at superior solar conjunction
03 Oct 2019  –  Mercury at aphelion

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