© NASA/JPL/MESSENGER

Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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Mercury will reach half phase in its 2014 evening apparition. It will be shining brightly at mag 0.1.

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 sunset on 11 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 Cambridge local time.

Date Sun
sets at
Mercury
sets at
Altitude
at sunset
Direction
at sunset
18 Aug 201419:4020:11west
21 Aug 201419:3520:11west
24 Aug 201419:3020:09west
27 Aug 201419:2620:07west
30 Aug 201419:2120:04west
02 Sep 201419:1620:01west
05 Sep 201419:1019:56west
08 Sep 201419:0519:52west
11 Sep 201419:0019:47west
14 Sep 201418:5519:42west
17 Sep 201418:4919:36west
20 Sep 201418:4419:30south-west
23 Sep 201418:3919:23south-west
26 Sep 201418:3319:15south-west
29 Sep 201418:2819:07south-west
02 Oct 201418:2318:57south-west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2014 evening apparition of Mercury
16 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 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 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
Sunrise
06:35
Sunset
18:34
Twilight ends
20:08
Twilight begins
05:01

2-day old moon
Waxing Crescent

4%

2 days old

Planets
Rise Culm. Set
Mercury 08:55 14:05 19:15
Venus 05:55 12:09 18:23
Moon 08:59 14:22 19:45
Mars 12:16 16:48 21:20
Jupiter 02:26 09:33 16:41
Saturn 10:30 15:34 20:37
All times shown in EDT.

Source

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

21 Sep 2014  –  Mercury at greatest elongation east
31 Oct 2014  –  Mercury reaches highest point in morning sky
01 Nov 2014  –  Mercury at greatest elongation west
14 Jan 2015  –  Mercury at greatest elongation east

Image credit

© NASA/JPL/MESSENGER

Cambridge

Latitude:
Longitude:
Timezone:

42.38°N
71.11°W
EDT

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