© 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 Nov–Dec 1980 morning apparition. It will be shining brightly at mag -0.5.

From Ashburn , this apparition will be exceptionally well placed but tricky to observe, reaching a peak altitude of 17° above the horizon at sunrise on 20 Nov 1980.

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

Nov–Dec 1980 morning apparition of Mercury

03 Nov 1980 – Mercury at inferior solar conjunction
16 Nov 1980 – Mercury at dichotomy
19 Nov 1980 – Mercury at highest altitude in morning sky
19 Nov 1980 – Mercury at greatest elongation west
31 Dec 1980 – Mercury at superior solar conjunction

A graph of the phase of Mercury is available here.

Apparitions of Mercury

14 Jun 1980 – Evening apparition
01 Aug 1980 – Morning apparition
10 Oct 1980 – Evening apparition
19 Nov 1980 – Morning apparition
01 Feb 1981 – Evening apparition
15 Mar 1981 – Morning apparition
27 May 1981 – Evening 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 14h18m20s 11°18'S Virgo 7.2"
Sun 15h31m 19°04'S Libra 32'21"

The coordinates above are given in J2000.0.

The sky on 28 Mar 2024

The sky on 28 March 2024
Sunrise
06:58
Sunset
19:29
Twilight ends
21:00
Twilight begins
05:27

18-day old moon
Waning Gibbous

86%

18 days old

Planets
Rise Culm. Set
Mercury 07:29 14:14 20:59
Venus 06:24 12:10 17:56
Moon 22:00 03:15 08:23
Mars 05:43 11:09 16:35
Jupiter 08:42 15:39 22:36
Saturn 06:07 11:43 17:19
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

10 Oct 1980  –  Mercury at greatest elongation east
19 Nov 1980  –  Mercury at highest altitude in morning sky
19 Nov 1980  –  Mercury at greatest elongation west
01 Feb 1981  –  Mercury at greatest elongation east

Image credit

© NASA/JPL/MESSENGER

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