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 0.2.

From Cambridge , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 9° above the horizon at sunrise on 7 Apr 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
20 Mar 201906:5006:13east
23 Mar 201906:4506:01east
26 Mar 201906:3905:51east
29 Mar 201906:3405:42east
01 Apr 201906:2905:36east
04 Apr 201906:2405:30east
07 Apr 201906:1905:26east
10 Apr 201906:1405:22east
13 Apr 201906:0905:18east
16 Apr 201906:0405:15east
19 Apr 201905:5905:13east
22 Apr 201905:5505:10east
25 Apr 201905:5005:08east
28 Apr 201905:4605:06east
01 May 201905:4205:05east
04 May 201905:3805:04east

A graph of the phase of Mercury is available here.

Observing Mercury

The 2019 morning apparition of Mercury
14 Mar 2019 – Mercury at inferior solar conjunction
09 Apr 2019 – Mercury reaches highest point in morning sky
11 Apr 2019 – Mercury at greatest elongation west
12 Apr 2019 – Mercury at dichotomy
21 May 2019 – Mercury at superior 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 23h45m00s -04°00' Aquarius 7.6"
Sun 01h23m +08°47' Pisces 31'54"

The coordinates above are given in J2000.0.

The sky on 12 April 2019
Twilight ends
Twilight begins

7-day old moon
Waxing Gibbous


7 days old

Rise Culm. Set
Mercury 05:18 11:06 16:54
Venus 05:04 10:48 16:32
Moon 11:40 19:08 01:40
Mars 08:14 15:47 23:20
Jupiter 00:24 04:58 09:32
Saturn 02:11 06:50 11:29
All times shown in EDT.


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 Apr 2019  –  Mercury at dichotomy
21 May 2019  –  Mercury at superior solar conjunction
24 May 2019  –  Mercury at perihelion
17 Jun 2019  –  Mercury at dichotomy

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