© 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 dawn sky, shining brightly at mag -4.3.

From Fairfield, it will be difficult to observe as it will appear no higher than 18° above the horizon. It will rise at 03:13 (EST) – 2 hours and 7 minutes before the Sun – and reach an altitude of 18° above the eastern horizon before fading from view as dawn breaks at around 04:58.

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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:

25 Mar 2017 06:12 EDT – Venus at inferior solar conjunction
26 Apr 2017 14:36 EDT – Venus at greatest brightness
03 Jun 2017 01:58 EDT – Venus at greatest elongation west
04 Jun 2017 02:00 EDT – Venus at dichotomy

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 before sunrise Venus will rise each night; all times are given in Fairfield local time.

Date Sun
sets at
rises at
Altitude of Venus
at sunrise
Direction of Venus
at sunrise
28 May 201705:2303:2421°north-west
04 Jun 201705:2003:1422°north-west
11 Jun 201705:1803:0523°north-west
18 Jun 201705:1802:5825°north-west
25 Jun 201705:2002:5126°north-west
02 Jul 201705:2302:4627°north-west
09 Jul 201705:2702:4329°north-west
16 Jul 201705:3202:4229°north-west
23 Jul 201705:3802:4430°north-west
30 Jul 201705:4502:4830°north-west
06 Aug 201705:5202:5431°north-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 01h46m20s +08°31' Pisces 23.6"
Sun 04h48m +22°25' Taurus 31'31"

The coordinates above are given in J2000.0.

The sky on 04 June 2017
Twilight ends
Twilight begins

10-day old moon
Waxing Gibbous


10 days old

Rise Culm. Set
Mercury 04:28 11:35 18:41
Venus 03:14 09:47 16:21
Moon 15:53 21:37 02:51
Mars 06:22 13:58 21:35
Jupiter 14:58 20:48 02:42
Saturn 20:55 01:40 06:21
All times shown in EDT.


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

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
24 Mar 2020, 03:31 EDT  –  Venus at greatest elongation east

Image credit

© NASA/Ricardo Nunes




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