Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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The sky at

Mercury will be well placed for observation in the evening sky, shining brightly at mag -0.4.

From Ashburn, it will be difficult to observe as it will appear no higher than 13° above the horizon. It will become visible at around 20:07 (EST) as the dusk sky fades, 13° above your western horizon. It will then sink towards the horizon, setting 1 hour and 42 minutes after the Sun at 21:25.

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

Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time.

It is observable only for a few days each time it reaches greatest separation from the Sun – moments referred to as greatest elongation.

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 in coming weeks

The key moments in this apparition of Mercury are as follows:

23 Mar 2016 15:58 EDT – Mercury at superior solar conjunction
15 Apr 2016 03:57 EDT – Mercury at dichotomy
18 Apr 2016 07:34 EDT – Mercury at greatest elongation east
09 May 2016 10:57 EDT – Transit of Mercury
09 May 2016 11:06 EDT – Mercury at inferior solar conjunction

Over coming weeks, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare. The table below lists how long Mercury will remain up after sunset each night; all times are given in Ashburn local time.

Date Sun
sets at
sets at
Altitude of Mercury
at sunset
Direction of Mercury
at sunset
08 Apr 201619:3521:0014°west
15 Apr 201619:4221:2818°west
22 Apr 201619:4921:3418°west
29 Apr 201619:5621:1313°west
06 May 201620:0220:30west
13 May 201620:0919:37-5°north-west
20 May 201620:1518:53-15°north-west
27 May 201620:2118:28-20°north-west
03 Jun 201620:2618:21-21°north-west
10 Jun 201620:3018:31-20°north-west
17 Jun 201620:3318:55-16°north-west

A graph of the phase of Mercury is available here.

Mercury's position

The coordinates of Mercury when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Mercury 02h46m30s +18°38' Aries 7.1"
Sun 01h34m +09°52' Pisces 31'52"

The coordinates above are given in J2000.0.

The sky on 15 April 2016
Twilight ends
Twilight begins

8-day old moon
Waxing Gibbous


8 days old

Rise Culm. Set
Mercury 07:13 14:21 21:28
Venus 06:05 12:19 18:33
Moon 14:05 20:50 02:56
Mars 23:08 04:02 08:52
Jupiter 16:05 22:33 05:06
Saturn 23:38 04:33 09:24
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 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

06 Feb 2016, 22:30 EST  –  Mercury at greatest elongation west
18 Apr 2016, 07:34 EDT  –  Mercury at greatest elongation east
09 May 2016, 10:57 EDT  –  Transit of Mercury
05 Jun 2016, 08:43 EDT  –  Mercury at greatest elongation west

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