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 2013 morning apparition. It will be shining brightly at mag 0.2.

From Fairfield , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 10° above the horizon at sunrise on 24 Mar 2013.

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 Fairfield local time.

Date Sun
rises at
rises at
at sunrise
at sunrise
09 Mar 201306:1605:37east
12 Mar 201307:1106:23east
15 Mar 201307:0606:12east
18 Mar 201307:0106:04east
21 Mar 201306:5605:5710°east
24 Mar 201306:5105:5210°east
27 Mar 201306:4605:4810°east
30 Mar 201306:4105:45east
02 Apr 201306:3605:42east
05 Apr 201306:3105:39east
08 Apr 201306:2605:37east
11 Apr 201306:2205:36east
14 Apr 201306:1705:34east
17 Apr 201306:1205:32east
20 Apr 201306:0805:31east
23 Apr 201306:0305:30east

A graph of the phase of Mercury is available here.

Observing Mercury

The 2013 morning apparition of Mercury
04 Mar 2013 – Mercury at inferior solar conjunction
29 Mar 2013 – Mercury reaches highest point in morning sky
31 Mar 2013 – Mercury at dichotomy
31 Mar 2013 – Mercury at greatest elongation west

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 22h59m20s -08°07' Aquarius 7.6"
Sun 00h39m +04°14' Pisces 32'01"

The coordinates above are given in J2000.0.

The sky on 31 March 2013
Twilight ends
Twilight begins

20-day old moon
Waning Gibbous


20 days old

Rise Culm. Set
Mercury 05:43 11:17 16:52
Venus 06:47 13:02 19:17
Moon 23:30 04:22 09:15
Mars 06:51 13:12 19:34
Jupiter 09:32 16:57 00:25
Saturn 21:29 02:52 08:12
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

31 Mar 2013  –  Mercury at dichotomy
31 Mar 2013  –  Mercury at greatest elongation west
01 Apr 2013  –  Mercury at aphelion
11 May 2013  –  Mercury at superior solar conjunction

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