Mercury at greatest brightness

Tue, 09 Feb 2016 at15:40 EST(709 days ago)
20:40 UTC

Dominic Ford, Editor
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The sky at

In the southern hemisphere Mercury will be well placed for observation in the dawn sky, shining brightly at mag -0.1.

From Ashburn (click to change) however, it will not be observable – it will reach its highest point in the sky during daytime and will be no higher than 7° above the horizon at dawn.

Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time.

It is observable only for a few days each time it reaches greatest separation from the Sun – moments referred to as greatest elongation.

Mercury's brightness

Mercury's brightness depends on two factors: its closeness to the Earth, and its phase. Its 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 reaches its brightest when it is still a crescent – with less than half of its disk illuminated. This is because it is much closer to the Earth during its crescent phases than at other times.

As a result, during evening apparitions, Mercury reaches maximum brightness a few days after it is at greatest separation from the Sun, which always coincides with it showing half-phase (dichotomy).

Conversely, during morning apparitions, Mercury reaches maximum brightness a few days before it is at greatest separation from the Sun.

Mercury in coming weeks

The key moments in this apparition of Mercury are as follows:

14 Jan 2016 08:59 EST – Mercury at inferior solar conjunction
01 Feb 2016 07:12 EST – Mercury at dichotomy
06 Feb 2016 22:30 EST – Mercury at greatest elongation west
09 Feb 2016 15:40 EST – Mercury at greatest brightness

Over coming weeks, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare. The table below lists how long before sunrise Mercury will rise each night; all times are given in Ashburn local time.

Date Sun
sets at
rises at
Altitude of Mercury
at sunrise
Direction of Mercury
at sunrise
02 Feb 201607:1505:4613°west
09 Feb 201607:0805:4812°west
16 Feb 201607:0005:54west
23 Feb 201606:5006:01west
01 Mar 201606:4106:06west
08 Mar 201606:3006:09west
15 Mar 201607:1907:12west
22 Mar 201607:0807:14-1°west
29 Mar 201606:5707:15-4°west
05 Apr 201606:4607:16-6°west
12 Apr 201606:3607:15-7°west

A graph of the brightness of Mercury is available here.

Mercury's position

The coordinates of Mercury when it reaches greatest brightness will be:

Object Right Ascension Declination Constellation Angular Size
Mercury 19h47m10s -20°54' Sagittarius 6.5"
Sun 21h30m -14°42' Capricornus 32'25"

The coordinates above are given in J2000.0.

The sky on 09 February 2016
Sunrise 07:08
Sunset 17:38
Twilight ends
Twilight begins

1-day old moon
Age of Moon
1 days

All times shown in EST.
Rise Culm. Set
Mercury 05:48 10:39 15:30
Venus 05:33 10:21 15:09
Moon 07:44 13:20 18:56
Mars 00:51 06:01 11:10
Jupiter 20:02 02:25 08:43
Saturn 02:56 07:47 12:38


The circumstances of this event were computed using the DE405 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

06 Feb 2016, 22:30 EST  –  Mercury at greatest elongation west
18 Apr 2016, 07:34 EDT  –  Mercury at greatest elongation east
09 May 2016, 07:12 EDT  –  Transit of Mercury
05 Jun 2016, 08:43 EDT  –  Mercury at greatest elongation west

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