© NASA/Ricardo Nunes

Venus at greatest brightness

Dominic Ford, Editor
From the Inner Planets feed

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The sky at

In the southern hemisphere Venus will be well placed for observation in the evening sky, shining brightly at mag -4.6.

From Ashburn however, it will not be observable – it will reach its highest point in the sky during daytime and will be no higher than 7° above the horizon at dusk.

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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 brightness

Venus'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.

Venus 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, Venus 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, Venus reaches maximum brightness a few days before it is at greatest separation from the Sun.

Venus in coming weeks

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

15 Aug 2018 01:09 EDT – Venus at dichotomy
17 Aug 2018 03:58 EDT – Venus at greatest elongation east
25 Sep 2018 00:17 EDT – Venus at greatest brightness
26 Oct 2018 10:11 EDT – Venus at inferior solar conjunction
29 Nov 2018 21:23 EST – Venus at greatest brightness

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
18 Sep 201819:1020:2512°south-west
25 Sep 201818:5920:0110°south-west
02 Oct 201818:4819:35south-west
09 Oct 201818:3719:05south-west
16 Oct 201818:2718:32south-west
23 Oct 201818:1717:58-3°south-west
30 Oct 201818:0817:26-8°west
06 Nov 201817:0116:01-11°west
13 Nov 201816:5415:37-15°west
20 Nov 201816:4915:16-18°west
27 Nov 201816:4514:59-21°west

A graph of the brightness of Venus is available here.

Venus's position

The coordinates of Venus when it reaches greatest brightness will be:

Object Right Ascension Declination Constellation Angular Size
Venus 14h16m10s -20°13' Virgo 42.0"
Sun 12h06m -00°43' Virgo 31'53"

The coordinates above are given in J2000.0.

The sky on 25 September 2018
Twilight ends
Twilight begins

16-day old moon
Waning Gibbous


16 days old

Rise Culm. Set
Mercury 07:17 13:16 19:14
Venus 10:15 15:08 20:01
Moon 19:49 01:11 07:03
Mars 16:38 21:19 02:03
Jupiter 11:01 16:06 21:11
Saturn 14:18 19:02 23:46
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

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
13 Aug 2020, 09:03 EDT  –  Venus at greatest elongation west

Image credit

© NASA/Ricardo Nunes




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