© 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 Jan–Feb 2030 morning apparition. It will be shining brightly at mag -0.1.

From Seattle , 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 sunrise on 15 Jan 2030.

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Jan–Feb 2030 morning apparition of Mercury

31 Dec 2029 – Mercury at inferior solar conjunction
14 Jan 2030 – Mercury at highest altitude in morning sky
16 Jan 2030 – Mercury at dichotomy
22 Jan 2030 – Mercury at greatest elongation west

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

Date Sun
rises at
Mercury
rises at
Altitude
at sunrise
Direction
at sunrise
Mag Phase
03 Jan 203007:5507:12south-east3.64%
06 Jan 203007:5406:46south-east1.813%
09 Jan 203007:5306:2811°south-east0.724%
12 Jan 203007:5206:1812°south-east0.235%
15 Jan 203007:5006:1212°south-east-0.145%
18 Jan 203007:4806:1112°south-east-0.254%
21 Jan 203007:4506:1311°south-east-0.261%
24 Jan 203007:4206:1610°south-east-0.267%
27 Jan 203007:3906:20south-east-0.272%
30 Jan 203007:3606:25south-east-0.276%
02 Feb 203007:3206:29south-east-0.279%
05 Feb 203007:2806:33south-east-0.282%
08 Feb 203007:2306:37south-east-0.285%

Mercury will brighten rapidly at the start of its morning apparition as it emerges from inferior conjunction. Prior to its apparition, it passed between the Earth and Sun, at which time it had its unilluminated side turned towards the Earth and so appeared as a thin, barely illuminated crescent. As the apparition proceeds, this crescent waxes and becomes gibbous.

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 after it reaches its highest point in the sky – when it will show a gibbous phase – than in the days beforehand.

Altitude of Mercury at sunrise

A graph of the phase of Mercury is available here.

Apparitions of Mercury

19 Aug 2029 – Evening apparition
01 Oct 2029 – Morning apparition
13 Dec 2029 – Evening apparition
22 Jan 2030 – Morning apparition
03 Apr 2030 – Evening apparition
20 May 2030 – Morning apparition
01 Aug 2030 – 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 18h12m50s 21°13'S Sagittarius 7.5"
Sun 19h53m 20°52'S Sagittarius 32'31"

The coordinates above are given in J2000.0.

The sky on 16 Jan 2030

The sky on 16 January 2030
Sunrise
07:49
Sunset
16:45
Twilight ends
18:35
Twilight begins
05:59

12-day old moon
Waxing Gibbous

94%

12 days old

Planets
Rise Culm. Set
Mercury 06:13 10:37 15:00
Venus 06:20 11:07 15:53
Moon 14:06 22:16 06:23
Mars 09:18 14:21 19:23
Jupiter 03:04 07:47 12:30
Saturn 12:14 19:26 02:37
All times shown in PST.

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

14 Jan 2030  –  Mercury at highest altitude in morning sky
22 Jan 2030  –  Mercury at greatest elongation west
04 Apr 2030  –  Mercury at highest altitude in evening sky
03 Apr 2030  –  Mercury at greatest elongation east

Image credit

© NASA/JPL/MESSENGER

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