© NASA/Ricardo Nunes

Venus at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

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The sky at

Venus will be well placed for observation in the evening sky, shining brightly at mag -4.4.

From Ashburn, it will become visible at around 17:26 (EST) as the dusk sky fades, 35° above your south-western horizon. It will then sink towards the horizon, setting 3 hours and 55 minutes after the Sun at 21:02.

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Venus'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 weeks each time it reaches greatest separation from the Sun – moments referred to as greatest elongation.

On these occasions, however, Venus is so bright and conspicuous that it becomes the third brightest object in the sky after the Sun and Moon. It is often called the morning or evening star.

Venus's phase

Venus'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.

Venus 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 hours, only because Venus's orbit is not quite perfectly aligned with the ecliptic.

Venus in coming weeks

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

12 Jan 2017 10:52 EST – Venus at greatest elongation east
14 Jan 2017 08:13 EST – Venus at dichotomy
18 Feb 2017 10:42 EST – Venus at greatest brightness
25 Mar 2017 06:12 EDT – Venus at inferior solar conjunction

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

Date Sun
sets at
sets at
Altitude of Venus
at sunset
Direction of Venus
at sunset
07 Jan 201716:5820:5435°south-west
14 Jan 201717:0521:0337°south-west
21 Jan 201717:1321:1139°south-west
28 Jan 201717:2121:1640°south-west
04 Feb 201717:2921:1841°south-west
11 Feb 201717:3721:1740°south-west
18 Feb 201717:4521:1038°south-west
25 Feb 201717:5320:5834°west
04 Mar 201718:0020:3629°west
11 Mar 201718:0820:0422°west
18 Mar 201719:1520:2212°west

A graph of the phase of Venus is available here.

Venus's position

The coordinates of Venus when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Venus 22h52m00s -07°34' Aquarius 24.9"
Sun 19h44m -21°14' Sagittarius 32'31"

The coordinates above are given in J2000.0.

The sky on 14 January 2017
Twilight ends
Twilight begins

16-day old moon
Waning Gibbous


16 days old

Rise Culm. Set
Mercury 05:47 10:37 15:26
Venus 09:46 15:25 21:03
Moon 20:06 01:53 08:43
Mars 10:07 15:55 21:42
Jupiter 00:18 05:57 11:36
Saturn 05:14 10:01 14:48
All times shown in EST.


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

12 Jan 2017, 10:52 EST  –  Venus at greatest elongation east
03 Jun 2017, 01:58 EDT  –  Venus at greatest elongation west
17 Aug 2018, 03:58 EDT  –  Venus at greatest elongation east
06 Jan 2019, 01:02 EST  –  Venus at greatest elongation west

Image credit

© NASA/Ricardo Nunes




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