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BAA Observing calendar

Venus at greatest brightness

Thursday, 2019, August 15 - 12:36

In the southern hemisphere Venus will be well placed for observation in the evening sky, shining brightly at mag -3.9.

From London however, it will not be readily observable since it will be very close to the Sun, at a separation of only 1° from it.

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:

14 Aug 2019 06:33 BST  – Venus at superior solar conjunction
15 Aug 2019 12:36 BST  – 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 London local time.

Date Sun
sets at
Venus
sets at
Altitude of Venus
at sunset
Direction of Venus
at sunset
08 Aug 2019 20:33 20:39 north-west
15 Aug 2019 20:20 20:31 north-west
22 Aug 2019 20:06 20:21 west
29 Aug 2019 19:51 20:09 west
05 Sep 2019 19:36 19:56 west
12 Sep 2019 19:20 19:42 west
19 Sep 2019 19:04 19:29 west
26 Sep 2019 18:48 19:15 west
03 Oct 2019 18:32 19:01 west
10 Oct 2019 18:16 18:49 south-west
17 Oct 2019 18:01 18:37 south-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 09h40m50s +15°14' Leo 9.6"
Sun 09h37m +14°08' Leo 31'34"

The coordinates above are given in J2000.0.

This entry in the observing calendar was provided by In-The-Sky.org

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