© 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 2018 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 9° above the horizon at sunrise on 26 Apr 2018.

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
Mercury
rises at
Altitude
at sunrise
Direction
at sunrise
08 Apr 201806:2505:51west
11 Apr 201806:2105:40west
14 Apr 201806:1605:31west
17 Apr 201806:1105:23west
20 Apr 201806:0705:16north-west
23 Apr 201806:0205:10north-west
26 Apr 201805:5805:05north-west
29 Apr 201805:5405:01north-west
02 May 201805:5004:57north-west
05 May 201805:4704:54north-west
08 May 201805:4304:51north-west
11 May 201805:4004:49north-west
14 May 201805:3704:48north-west
17 May 201805:3404:47north-west
20 May 201805:3104:47north-west
23 May 201805:2904:49north-west

A graph of the phase of Mercury is available here.

Observing Mercury

The 2018 morning apparition of Mercury
01 Apr 2018 – Mercury at inferior solar conjunction
29 Apr 2018 – Mercury at greatest elongation west
01 May 2018 – Mercury reaches highest point in morning sky
03 May 2018 – Mercury at dichotomy
05 Jun 2018 – Mercury at superior solar conjunction

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 01h05m10s +03°43' Pisces 7.5"
Sun 02h41m +15°43' Aries 31'43"

The coordinates above are given in J2000.0.

The sky on 03 May 2018
Sunrise
05:47
Sunset
19:50
Twilight ends
21:37
Twilight begins
04:00

17-day old moon
Waning Gibbous

87%

17 days old

Planets
Rise Culm. Set
Mercury 04:56 11:12 17:28
Venus 07:12 14:42 22:13
Moon 23:28 03:27 08:19
Mars 01:15 05:53 10:31
Jupiter 20:06 01:15 06:20
Saturn 00:06 04:45 09:25
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

01 May 2018  –  Mercury reaches highest point in morning sky
03 Jul 2018  –  Mercury reaches highest point in evening sky
12 Jul 2018  –  Mercury at greatest elongation east
26 Aug 2018  –  Mercury at greatest elongation west

Image credit

© NASA/JPL/MESSENGER

Fairfield

Latitude:
Longitude:
Timezone:

41.14°N
73.26°W
EDT

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