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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 2014 evening apparition. It will be shining brightly at mag 0.1.

From Ashburn , 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 sunset on 12 Sep 2014.

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 Ashburn local time.

Date Sun
sets at
sets at
at sunset
at sunset
19 Aug 201419:5920:33west
22 Aug 201419:5520:33west
25 Aug 201419:5120:33west
28 Aug 201419:4620:31west
31 Aug 201419:4220:29west
03 Sep 201419:3720:26west
06 Sep 201419:3320:23west
09 Sep 201419:2820:19west
12 Sep 201419:2320:15west
15 Sep 201419:1820:10west
18 Sep 201419:1320:05west
21 Sep 201419:0919:59south-west
24 Sep 201419:0419:53south-west
27 Sep 201418:5919:45south-west
30 Sep 201418:5419:37south-west
03 Oct 201418:4919:26south-west
06 Oct 201418:4519:14south-west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2014 evening apparition of Mercury
08 Sep 2014 – Mercury reaches highest point in evening sky
21 Sep 2014 – Mercury at greatest elongation east
26 Sep 2014 – 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 13h42m10s -14°01' Virgo 7.5"
Sun 12h11m -01°12' Virgo 31'54"

The coordinates above are given in J2000.0.

The sky on 26 September 2014
Twilight ends
Twilight begins

2-day old moon
Waxing Crescent


2 days old

Rise Culm. Set
Mercury 09:16 14:32 19:48
Venus 06:23 12:36 18:49
Moon 09:23 14:50 20:16
Mars 12:33 17:15 21:57
Jupiter 03:00 10:00 17:00
Saturn 10:50 16:01 21:11
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

26 Sep 2014  –  Mercury at dichotomy
16 Oct 2014  –  Mercury at inferior solar conjunction
25 Oct 2014  –  Mercury at perihelion
30 Oct 2014  –  Mercury at dichotomy

Image credit

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