© 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 2017 morning apparition. It will be shining brightly at mag -0.1.

From Cambridge , this apparition will not be one of the most prominent and tricky to observe, reaching a peak altitude of 14° above the horizon at sunrise on 13 Jan 2017.

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 Cambridge local time.

Date Sun
sets at
Mercury
rises at
Altitude
at sunrise
Direction
at sunrise
01 Jan 201707:1506:23south-west
04 Jan 201707:1506:0011°west
07 Jan 201707:1505:4413°west
10 Jan 201707:1405:3513°west
13 Jan 201707:1305:3114°west
16 Jan 201707:1205:3114°west
19 Jan 201707:1005:3313°west
22 Jan 201707:0805:3712°west
25 Jan 201707:0505:4211°west
28 Jan 201707:0305:4710°west
31 Jan 201707:0005:52west
03 Feb 201706:5705:57west
06 Feb 201706:5306:01west
09 Feb 201706:4906:05west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2017 morning apparition of Mercury
28 Dec 2016 – Mercury at inferior solar conjunction
12 Jan 2017 – Mercury reaches highest point in morning sky
13 Jan 2017 – Mercury at dichotomy
19 Jan 2017 – 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 18h02m10s -21°11' Sagittarius 7.4"
Sun 19h42m -21°21' Sagittarius 32'31"

The coordinates above are given in J2000.0.

The sky on 13 January 2017
Sunrise
07:10
Sunset
16:33
Twilight ends
18:13
Twilight begins
05:31

15-day old moon
Waning Gibbous

97%

15 days old

Planets
Rise Culm. Set
Mercury 05:31 10:12 14:53
Venus 09:26 14:59 20:33
Moon 18:29 00:30 07:39
Mars 09:46 15:30 21:15
Jupiter 23:55 05:35 11:11
Saturn 05:01 09:39 14:16
All times shown in EST.

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

12 Jan 2017  –  Mercury reaches highest point in morning sky
19 Jan 2017  –  Mercury at greatest elongation west
01 Apr 2017  –  Mercury at greatest elongation east
03 Apr 2017  –  Mercury reaches highest point in evening sky

Image credit

© NASA/JPL/MESSENGER

Cambridge

Latitude:
Longitude:
Timezone:

42.38°N
71.11°W
EDT

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