© 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 Jul–Sep 2002 evening apparition. It will be shining brightly at mag 0.2.

From San Diego , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 12° above the horizon at sunset on 23 Aug 2002.

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Jul–Sep 2002 evening apparition of Mercury

20 Jul 2002 – Mercury at superior solar conjunction
21 Aug 2002 – Mercury at highest altitude in evening sky
31 Aug 2002 – Mercury at greatest elongation east
03 Sep 2002 – Mercury at dichotomy
27 Sep 2002 – Mercury at inferior solar conjunction

A graph of the phase of Mercury is available here.

Apparitions of Mercury

21 Feb 2002 – Morning apparition
03 May 2002 – Evening apparition
21 Jun 2002 – Morning apparition
31 Aug 2002 – Evening apparition
12 Oct 2002 – Morning apparition
26 Dec 2002 – Evening apparition
03 Feb 2003 – 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 12h25m50s 5°47'S Virgo 7.5"
Sun 10h51m 7°18'N Leo 31'42"

The coordinates above are given in J2000.0.

The sky on 29 Mar 2024

The sky on 29 March 2024
Sunrise
06:37
Sunset
19:06
Twilight ends
20:29
Twilight begins
05:14

19-day old moon
Waning Gibbous

80%

19 days old

Planets
Rise Culm. Set
Mercury 07:13 13:50 20:27
Venus 05:59 11:50 17:40
Moon 22:33 03:45 08:52
Mars 05:12 10:47 16:21
Jupiter 08:29 15:14 22:00
Saturn 05:36 11:18 16:59
All times shown in PDT.

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

31 Aug 2002  –  Mercury at greatest elongation east
13 Oct 2002  –  Mercury at highest altitude in morning sky
12 Oct 2002  –  Mercury at greatest elongation west
26 Dec 2002  –  Mercury at greatest elongation east

Image credit

© NASA/JPL/MESSENGER

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32.72°N
117.16°W
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