© 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 Mar–Apr 2024 evening apparition. It will be shining brightly at mag -0.5.

From Fairfield , this apparition will be well placed but tricky to observe, reaching a peak altitude of 16° above the horizon at sunset on 27 Mar 2024.

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

Mar–Apr 2024 evening apparition of Mercury

28 Feb 2024 – Mercury at superior solar conjunction
22 Mar 2024 – Mercury at dichotomy
23 Mar 2024 – Mercury at highest altitude in evening sky
24 Mar 2024 – Mercury at greatest elongation east
11 Apr 2024 – Mercury at inferior solar conjunction

The table below lists the altitude of Mercury at sunset over the course of the apparition. All times are given in Fairfield local time.

Date Sun
sets at
Mercury
sets at
Altitude
at sunset
Direction
at sunset
Mag Phase
09 Mar 202417:5518:33west-1.494%
12 Mar 202418:5719:51west-1.389%
15 Mar 202419:0320:0712°west-1.181%
18 Mar 202419:0520:2414°west-1.070%
21 Mar 202419:0620:3616°west-0.758%
24 Mar 202419:1220:4416°west-0.446%
27 Mar 202419:1420:4816°west0.234%
30 Mar 202419:1620:4216°west0.923%
02 Apr 202419:2220:3512°west1.814%
05 Apr 202419:2420:2110°west3.07%
08 Apr 202419:2620:00west4.52%

Mercury will fade rapidly towards the end of the apparition as it heads towards inferior conjunction, when it will pass between the Earth and Sun. At inferior conjunction, the planet turns its unilluminated side towards the Earth, and so appears as a thin, barely illuminated crescent.

Since Mercury can only ever be observed in twilight, it is particularly difficult to find when it is in a thin crescent phase. Thus, it will be significantly easier to see in the days before it reaches its highest point in the sky than in the days after.

Altitude of Mercury at sunset

A graph of the phase of Mercury is available here.

Apparitions of Mercury

22 Sep 2023 – Morning apparition
04 Dec 2023 – Evening apparition
12 Jan 2024 – Morning apparition
24 Mar 2024 – Evening apparition
09 May 2024 – Morning apparition
21 Jul 2024 – Evening apparition
04 Sep 2024 – 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 01h14m40s 10°09'N Pisces 7.1"
Sun 00h09m +01°03' Pisces 32'05"

The coordinates above are given in J2000.0.

The sky on 22 March 2024
Sunrise
06:50
Sunset
19:10
Twilight ends
20:42
Twilight begins
05:18

12-day old moon
Waxing Gibbous

97%

12 days old

Planets
Rise Culm. Set
Mercury 07:25 14:03 20:41
Venus 06:17 11:52 17:27
Moon 16:44 23:39 06:24
Mars 05:44 11:01 16:19
Jupiter 08:45 15:44 22:44
Saturn 06:14 11:47 17:20
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

12 Jan 2024  –  Mercury at greatest elongation west
23 Mar 2024  –  Mercury at highest altitude in evening sky
24 Mar 2024  –  Mercury at greatest elongation east
09 May 2024  –  Mercury at greatest elongation west

Image credit

© NASA/JPL/MESSENGER

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