Mercury at greatest brightness

Wed, 11 Jan 2017 at06:29 EST(6 days ago)
11:29 UTC

Dominic Ford, Editor
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The sky at

Mercury will be well placed for observation in the dawn sky, shining brightly at mag -2.2.

From Newark (click to change), it will be difficult to observe as it will appear no higher than 11° above the horizon. It will rise at 05:41 (EST) – 1 hour and 38 minutes before the Sun – and reach an altitude of 11° above the south-eastern horizon before fading from view as dawn breaks at around 06:59.

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 Dec 2016 11:40 EST – Mercury at dichotomy
15 Dec 2016 01:59 EST – Mercury at greatest brightness
28 Dec 2016 13:41 EST – Mercury at inferior solar conjunction
11 Jan 2017 06:29 EST – Mercury at greatest brightness
13 Jan 2017 17:02 EST – Mercury at dichotomy
19 Jan 2017 08:45 EST – Mercury at greatest elongation west

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 Newark local time.

Date Sun
sets at
rises at
Altitude of Mercury
at sunrise
Direction of Mercury
at sunrise
04 Jan 201707:1906:0810°west
11 Jan 201707:1805:4113°west
18 Jan 201707:1605:4013°west
25 Jan 201707:1105:4911°west
01 Feb 201707:0506:01west
08 Feb 201706:5806:12west
15 Feb 201706:4906:20west
22 Feb 201706:3906:26west
01 Mar 201706:2906:29west
08 Mar 201706:1806:30-2°west
15 Mar 201707:0707:30-4°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 17h56m40s -20°49' Sagittarius 7.9"
Sun 19h31m -21°45' Sagittarius 32'31"

The coordinates above are given in J2000.0.

The sky on 11 January 2017
Sunrise: 07:19
Sunset: 16:48
from 05:41
until 18:25

13-day old moon
Age of Moon:
13 days

All times shown in EST.
Rise Culm. Set
Mercury 05:41 10:28 15:15
Venus 09:40 15:12 20:44
Moon 16:34 23:45 05:56
Mars 10:01 15:45 21:29
Jupiter 00:17 05:54 11:32
Saturn 05:16 09:58 14:40


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

11 Jan 2017, 06:29 ESTMercury at greatest brightness
13 Jan 2017, 17:02 ESTMercury at dichotomy
19 Jan 2017, 08:45 ESTMercury at greatest elongation west
07 Mar 2017, 19:15 ESTMercury at superior solar conjunction

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