© NASA/JPL/MESSENGER

Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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The sky at

Mercury will reach half phase in its 2016 morning apparition. It will be shining brightly at mag -0.5.

From Ashburn , this apparition will be well placed but tricky to observe, reaching a peak altitude of 16° above the horizon at sunrise on 29 Sep 2016.

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 Ashburn local time.

Date Sun
sets at
Mercury
rises at
Altitude
at sunrise
Direction
at sunrise
17 Sep 201606:5506:13west
20 Sep 201606:5805:5312°west
23 Sep 201607:0005:3914°west
26 Sep 201607:0305:3316°west
29 Sep 201607:0605:3416°west
02 Oct 201607:0905:4015°west
05 Oct 201607:1205:5014°west
08 Oct 201607:1406:0312°west
11 Oct 201607:1706:1610°west
14 Oct 201607:2006:30west
17 Oct 201607:2306:45west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2016 morning apparition of Mercury
12 Sep 2016 – Mercury at inferior solar conjunction
28 Sep 2016 – Mercury at greatest elongation west
28 Sep 2016 – Mercury at dichotomy
01 Oct 2016 – Mercury reaches highest point in morning sky

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 11h17m20s +05°47' Leo 7.1"
Sun 12h21m -02°17' Virgo 31'55"

The coordinates above are given in J2000.0.

The sky on 28 September 2016
Sunrise
07:02
Sunset
18:56
Twilight ends
20:25
Twilight begins
05:33

27-day old moon
Waning Crescent

4%

27 days old

Planets
Rise Culm. Set
Mercury 05:33 11:55 18:17
Venus 09:35 14:52 20:10
Moon 04:50 11:20 17:49
Mars 14:10 18:41 23:11
Jupiter 06:53 12:54 18:55
Saturn 12:25 17:17 22:09
All times shown in EDT.

Warning

Never attempt to point a pair of binoculars or a telescope at an object close to the Sun. Doing so may result in immediate and permanent blindness.

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

28 Sep 2016  –  Mercury at greatest elongation west
01 Oct 2016  –  Mercury reaches highest point in morning sky
11 Dec 2016  –  Mercury at greatest elongation east
16 Dec 2016  –  Mercury reaches highest point in evening sky

Image credit

© NASA/JPL/MESSENGER

Ashburn

Latitude:
Longitude:
Timezone:

39.04°N
77.49°W
EDT

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