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Venus at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Venus
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Venus will reach half phase in its 2013–2014 evening apparition. It will be shining brightly at mag -4.4.

From Seattle , this apparition will not be one of the most prominent and tricky to observe, reaching a peak altitude of 17° above the horizon at sunset on 17 Dec 2013.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

The table below lists how high Venus will appear at sunset over the course of the apparition. All times are given in Seattle local time.

Date Sun
sets at
sets at
at sunset
at sunset
18 Sep 201319:1620:3611°south-west
28 Sep 201318:5620:2011°south-west
08 Oct 201318:3520:0811°south-west
18 Oct 201318:1620:0011°south-west
28 Oct 201317:5919:5711°south-west
07 Nov 201316:4318:5912°south
17 Nov 201316:3019:0314°south
27 Nov 201316:2119:0715°south
07 Dec 201316:1719:0517°south
17 Dec 201316:1718:5217°south-west
27 Dec 201316:2218:2215°south-west
06 Jan 201416:3117:34south-west

A graph of the phase of Venus is available here.

Observing Venus

The 2013–2014 evening apparition of Venus
30 Oct 2013 – Venus at dichotomy
31 Oct 2013 – Venus at greatest elongation east
09 Dec 2013 – Venus at greatest brightness
16 Dec 2013 – Venus reaches highest point in evening sky

Venus's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is lost in the Sun's glare much of the time.

It is observable for a few months each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions repeat roughly once every 1.6 years.

On these occasions, 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 star or the 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's position

The coordinates of Venus when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Venus 17h35m50s -26°56' Ophiuchus 24.7"
Sun 14h21m -14°04' Virgo 32'13"

The coordinates above are given in J2000.0.

The sky on 30 October 2013
Twilight ends
Twilight begins

25-day old moon
Waning Crescent


25 days old

Rise Culm. Set
Mercury 08:22 13:09 17:57
Venus 12:18 16:07 19:57
Moon 03:40 09:47 15:55
Mars 02:31 09:17 16:04
Jupiter 22:09 06:01 13:50
Saturn 08:17 13:19 18:20
All times shown in PDT.


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

30 Oct 2013  –  Venus at dichotomy
31 Oct 2013  –  Venus at greatest elongation east
09 Dec 2013  –  Venus at greatest brightness
17 Dec 2013  –  Venus reaches highest point in evening sky

Image credit

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