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Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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Mercury will reach half phase in its 2015 morning apparition. It will be shining brightly at mag 0.1.

From Fairfield , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 12° above the horizon at sunrise on 16 Feb 2015.

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
sets at
rises at
at sunrise
at sunrise
04 Feb 201507:0206:11west
07 Feb 201506:5905:5410°west
10 Feb 201506:5505:4211°west
13 Feb 201506:5105:3312°west
16 Feb 201506:4705:2812°west
19 Feb 201506:4305:2512°west
22 Feb 201506:3905:2411°west
25 Feb 201506:3505:2310°west
28 Feb 201506:3005:2410°west
03 Mar 201506:2505:24west
06 Mar 201506:2105:25west
09 Mar 201507:1606:25west
12 Mar 201507:1106:26west
15 Mar 201507:0606:26west
18 Mar 201507:0106:26west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2015 morning apparition of Mercury
30 Jan 2015 – Mercury at inferior solar conjunction
18 Feb 2015 – Mercury reaches highest point in morning sky
19 Feb 2015 – Mercury at dichotomy
24 Feb 2015 – 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 days 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 20h26m40s -18°19' Capricornus 7.6"
Sun 22h11m -11°13' Aquarius 32'21"

The coordinates above are given in J2000.0.

The sky on 19 February 2015
Twilight ends
Twilight begins

1-day old moon
Waxing Crescent


1 day old

Rise Culm. Set
Mercury 05:25 10:21 15:17
Venus 07:54 13:51 19:49
Moon 06:58 12:41 18:25
Mars 07:54 13:55 19:55
Jupiter 16:02 23:07 06:17
Saturn 01:14 06:07 11:00
All times shown in EST.


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

18 Feb 2015  –  Mercury reaches highest point in morning sky
24 Feb 2015  –  Mercury at greatest elongation west
07 May 2015  –  Mercury at greatest elongation east
09 May 2015  –  Mercury reaches highest point in evening sky

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