© 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 Sep–Oct 1997 morning 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 sunrise on 18 Sep 1997.

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

Sep–Oct 1997 morning apparition of Mercury

31 Aug 1997 – Mercury at inferior solar conjunction
16 Sep 1997 – Mercury at greatest elongation west
17 Sep 1997 – Mercury at dichotomy
17 Sep 1997 – Mercury at highest altitude in morning sky
13 Oct 1997 – Mercury at superior solar conjunction

A graph of the phase of Mercury is available here.

Apparitions of Mercury

05 Apr 1997 – Evening apparition
22 May 1997 – Morning apparition
03 Aug 1997 – Evening apparition
16 Sep 1997 – Morning apparition
28 Nov 1997 – Evening apparition
06 Jan 1998 – Morning apparition
19 Mar 1998 – 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 10h34m40s 9°43'N Leo 7.0"
Sun 11h39m 2°09'N Virgo 31'49"

The coordinates above are given in J2000.0.

The sky on 28 Mar 2024

The sky on 28 March 2024
Sunrise
06:40
Sunset
19:13
Twilight ends
20:47
Twilight begins
05:06

18-day old moon
Waning Gibbous

87%

18 days old

Planets
Rise Culm. Set
Mercury 07:08 13:57 20:46
Venus 06:08 11:53 17:38
Moon 21:47 02:58 08:00
Mars 05:29 10:52 16:16
Jupiter 08:21 15:22 22:23
Saturn 05:52 11:26 17:00
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 Sep 1997  –  Mercury at greatest elongation west
17 Sep 1997  –  Mercury at highest altitude in morning sky
28 Nov 1997  –  Mercury at greatest elongation east
02 Dec 1997  –  Mercury at highest altitude in evening sky

Image credit

© NASA/JPL/MESSENGER

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Fairfield

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41.14°N
73.26°W
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