Mercury at greatest brightness

Thu, 27 Oct 2016 at08:21 EDT(448 days ago)
12:21 UTC

Dominic Ford, Editor
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The sky at

In the southern hemisphere Mercury will be well placed for observation in the evening sky, shining brightly at mag -1.6.

From Ashburn (click to change) however, it will not be readily observable since it will be very close to the Sun, at a separation of only 0° from it.

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:

28 Sep 2016 13:07 EDT – Mercury at greatest elongation west
28 Sep 2016 13:35 EDT – Mercury at dichotomy
27 Oct 2016 08:21 EDT – Mercury at greatest brightness
27 Oct 2016 12:00 EDT – Mercury at superior solar conjunction

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 Mercury will remain up after sunset each night; all times are given in Ashburn local time.

Date Sun
sets at
sets at
Altitude of Mercury
at sunset
Direction of Mercury
at sunset
20 Oct 201618:2018:15-1°west
27 Oct 201618:1118:15west
03 Nov 201618:0318:16south-west
10 Nov 201616:5617:19south-west
17 Nov 201616:5017:25south-west
24 Nov 201616:4617:35south-west
01 Dec 201616:4317:48south-west
08 Dec 201616:4218:0311°south-west
15 Dec 201616:4418:0912°south-west
22 Dec 201616:4617:49south-west
29 Dec 201616:5116:53south-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 14h08m20s -12°24' Virgo 4.7"
Sun 14h08m -12°56' Virgo 32'11"

The coordinates above are given in J2000.0.

The sky on 27 October 2016
Sunrise 07:31
Sunset 18:14
Twilight ends
Twilight begins

26-day old moon
Age of Moon
26 days

All times shown in EDT.
Rise Culm. Set
Mercury 07:31 12:53 18:15
Venus 10:41 15:21 20:01
Moon 04:38 10:47 16:56
Mars 13:35 18:14 22:54
Jupiter 05:29 11:23 17:16
Saturn 10:43 15:33 20:24


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.


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

28 Sep 2016, 13:07 EDT  –  Mercury at greatest elongation west
11 Dec 2016, 02:45 EST  –  Mercury at greatest elongation east
19 Jan 2017, 08:45 EST  –  Mercury at greatest elongation west
01 Apr 2017, 01:52 EDT  –  Mercury at greatest elongation east

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