© NASA/Ricardo Nunes

Venus at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Venus
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Venus will reach half phase in its 1989–1990 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 19° above the horizon at sunset on 22 Dec 1989.

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

1989–1990 evening apparition of Venus

04 Apr 1989 – Venus at superior solar conjunction
07 Nov 1989 – Venus at dichotomy
08 Nov 1989 – Venus at greatest elongation east
16 Dec 1989 – Venus at greatest brightness
22 Dec 1989 – Venus at highest altitude in evening sky
18 Jan 1990 – Venus at inferior solar conjunction

A graph of the phase of Venus is available here.

Apparitions of Venus

15 Jan 1987 – Morning apparition
02 Apr 1988 – Evening apparition
22 Aug 1988 – Morning apparition
08 Nov 1989 – Evening apparition
30 Mar 1990 – Morning apparition
13 Jun 1991 – Evening apparition
01 Nov 1991 – Morning apparition

Observing Venus

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 days, 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 18h11m10s 26°56'S Sagittarius 24.8"
Sun 14h51m -16°28' Libra 32'17"

The coordinates above are given in J2000.0.

The sky on 21 January 2022
Twilight ends
Twilight begins

19-day old moon
Waning Gibbous


19 days old

Rise Culm. Set
Mercury 07:41 12:31 17:21
Venus 06:05 10:54 15:43
Moon 19:47 03:02 10:03
Mars 05:46 09:55 14:03
Jupiter 09:15 14:31 19:47
Saturn 08:27 13:11 17:54
All times shown in PST.


The circumstances of this event were computed using the DE430 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

17 Sep 1988  –  Venus at highest altitude in morning sky
08 Nov 1989  –  Venus at greatest elongation east
22 Dec 1989  –  Venus at highest altitude in evening sky
30 Mar 1990  –  Venus at greatest elongation west

Image credit

© NASA/Ricardo Nunes






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