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Venus at greatest elongation east

Dominic Ford, Editor
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The sky at

Venus will reach its greatest separation from the Sun in its 2016–2017 evening apparition. It will be shining brightly at mag -4.4.

From Washington , this apparition will be reasonably placed and prominent, reaching a peak altitude of 42° above the horizon at sunset on 31 Jan 2017.

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 above the horizon Venus will appear at sunset over the course of the apparition. All times are given in Washington local time.

Date Sun
sets at
Venus
sets at
Altitude
at sunset
Direction
at sunset
02 Nov 201618:3320:3518°south-west
12 Nov 201617:2419:4520°south-west
22 Nov 201617:1820:0022°south-west
02 Dec 201617:1520:1725°south-west
12 Dec 201617:1520:3628°south-west
22 Dec 201617:1920:5532°south-west
01 Jan 201717:2621:1235°south-west
11 Jan 201717:3521:2538°south-west
21 Jan 201717:4521:3641°south-west
31 Jan 201717:5621:4142°south-west
10 Feb 201718:0721:4041°south-west
20 Feb 201718:1721:2938°west
02 Mar 201718:2721:0431°west
12 Mar 201719:3721:2020°west
22 Mar 201719:4620:16west

A graph of the angular separation of Venus from the Sun around the time of greatest elongation is available here.

Observing Venus

The 2016–2017 evening apparition of Venus
12 Jan 2017 – Venus at greatest elongation east
14 Jan 2017 – Venus at dichotomy
31 Jan 2017 – Venus reaches highest point in evening sky
18 Feb 2017 – Venus at greatest brightness

Venus's orbit lies closer to the Sun than the Earth's, meaning 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.

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.

These apparitions repeat roughly once every 1.6 years, taking place alternately in the morning and evening skies, depending whether Venus lies to the east of the Sun or to the west.

When it lies to the east, it rises and sets a short time after the Sun and is visible in early evening twilight. When it lies to the west of the Sun, it rises and sets a short time before the Sun and is visible shortly before sunrise.

At each apparition, Venus reaches a maximum separation from the Sun of around 48°. However, some times of the year are more favourable for viewing Venus than others. From Washington, it reaches a peak altitude of between 20° and 46° above the horizon at sunset during each evening apparition, depending on the time of year. During its 2016–2017 apparition, it will peak at 42° above the horizon at sunset on 31 Jan 2017.

This variability over the course of the year is due to the inclination of the ecliptic to the horizon.

The inclination of the ecliptic to the horizon

The inclination of the ecliptic to the horizon changes over the course of the year, affecting how high planets close to the Sun appear in the sky.

At all times, Venus lies close to a line across the sky called the ecliptic, which is shown in yellow in the planetarium above. This line traces the path that the Sun takes through the zodiacal constellations every year, and shows the plane of the Earth's orbit around the Sun. Since all the planets circle the Sun in almost exactly the same plane, it also closely follows the planes of the orbits of the other planets, too.

When Venus is widely separated from the Sun, it is separated from it along the line of the ecliptic. But, at different times of year, the ecliptic meets the horizon at different angles at sunset. This would translate into Venus being at different altitudes above the horizon, even if its separation from the Sun was constant.

If the ecliptic meets the horizon at a shallow angle, then Venus has to be very widely separated from the Sun to appear much above the horizon. Conversely, if the ecliptic is almost perpendicular to the horizon, Venus may appear much higher in the sky, even if it is actually much closer to the Sun.

The seasonal dependence of this is that at sunset, the ecliptic makes its steepest angle to the horizon at the spring equinox – in March in the northern hemisphere, and in September in the southern hemisphere. Conversely, it meets the horizon at its shallowest angle at the autumn equinox. Because the seasons are opposite in the northern and southern hemispheres, a good apparition of Venus in one hemisphere will usually be badly placed in the other.

At sunrise, these dates are also inverted, so that for morning apparitions of Venus, the ecliptic makes its steepest angle to the horizon at the autumn equinox, and its shallowest angle to the horizon at the spring equinox.

The optimum time for an apparition of Venus

The maximum altitude of Venus during all its evening apparitions between 2000 and 2050, as a function of the day of the year on which greatest western elongation occurs. Different colours show the altitudes observed from different latitudes. Click to expand.

For this reason, the day when Venus reaches its widest separation from the Sun (greatest elongation) is not necessarily the same day when it appears highest in the sky at sunset. Venus typically appears highest in the sky a few days or weeks closer to the spring equinox than the moment of greatest elongation.

The inclination of the ecliptic plane to the horizon at Washington varies between 76° (sunset at the spring equinox) and 29° (sunset at the autumn equinox). On January 12, the ecliptic is inclined at 58° to the western sunset horizon, as shown by the yellow line in the planetarium above, meaning that this apparition of Venus will be reasonably placed and prominent, reaching a peak altitude of 42° above the horizon at sunset.

Venus's position

The position of Venus when it reaches greatest elongation will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Venus 22h45m10s -08°27' Aquarius -4.4 24.4"
Sun 19h36m -21°34' Sagittarius -26.7 32'31"

The coordinates above are given in J2000.0.

The sky on 12 January 2017
Sunrise
07:46
Sunset
17:36
Twilight ends
19:08
Twilight begins
06:14

14-day old moon
Waning Gibbous

99%

14 days old

Planets
Rise Culm. Set
Mercury 06:08 11:03 15:59
Venus 10:12 15:49 21:27
Moon 18:31 00:28 07:30
Mars 10:34 16:21 22:08
Jupiter 00:47 06:28 12:08
Saturn 05:39 10:31 15:24
All times shown in MST.

Source

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

12 Jan 2017  –  Venus at greatest elongation east
31 Jan 2017  –  Venus reaches highest point in evening sky
02 Jun 2017  –  Venus at greatest elongation west
27 Jul 2017  –  Venus reaches highest point in morning sky

Image credit

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Washington

Latitude:
Longitude:
Timezone:

37.13°N
113.51°W
MST

Color scheme