© NASA/JPL/MESSENGER

Mercury at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Mercury
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Mercury will reach half phase in its Dec 1981–Jan 1982 evening apparition. It will be shining brightly at mag -0.5.

From Ashburn , this apparition will not be one of the most prominent and tricky to observe, reaching a peak altitude of 14° above the horizon at sunset on 19 Jan 1982.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

Dec 1981–Jan 1982 evening apparition of Mercury

10 Dec 1981 – Mercury at superior solar conjunction
16 Jan 1982 – Mercury at greatest elongation east
17 Jan 1982 – Mercury at dichotomy
18 Jan 1982 – Mercury at highest altitude in evening sky
31 Jan 1982 – Mercury at inferior solar conjunction

A graph of the phase of Mercury is available here.

Apparitions of Mercury

14 Jul 1981 – Morning apparition
23 Sep 1981 – Evening apparition
02 Nov 1981 – Morning apparition
16 Jan 1982 – Evening apparition
26 Feb 1982 – Morning apparition
08 May 1982 – Evening apparition
26 Jun 1982 – Morning apparition

Observing Mercury

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 weeks 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 days, 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 21h16m20s 15°55'S Capricornus 7.2"
Sun 20h00m 20°34'S Sagittarius 32'30"

The coordinates above are given in J2000.0.

The sky on 29 Mar 2024

The sky on 29 March 2024
Sunrise
06:56
Sunset
19:30
Twilight ends
21:01
Twilight begins
05:25

19-day old moon
Waning Gibbous

82%

19 days old

Planets
Rise Culm. Set
Mercury 07:25 14:12 20:58
Venus 06:23 12:11 17:59
Moon 23:04 04:01 08:52
Mars 05:41 11:08 16:35
Jupiter 08:39 15:36 22:33
Saturn 06:03 11:39 17:15
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 DE430 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

16 Jan 1982  –  Mercury at greatest elongation east
18 Jan 1982  –  Mercury at highest altitude in evening sky
18 Feb 1982  –  Mercury at highest altitude in morning sky
26 Feb 1982  –  Mercury at greatest elongation west

Image credit

© NASA/JPL/MESSENGER

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