How to see the planets in the night sky, September 2020

Find out what planets are in the night sky in September, and how to see them.

Þ During the course of September, Mars will appear to increase in size by about 22%. Credit: Pete Lawrence

Mars now dominates the night sky, its gorgeous salmon-pink colour glowing like an ember within the constellation of Pisces. Fast approaching a favourable opposition in the middle of October 2020 month, Mars can be seen doing several remarkable things during September.

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To make the most of Mars at opposition, read our guide on how to observe Mars and our observing guide How to see the moons of Mars.

On 10 September the planet’s apparent eastward motion against the background stars stops as Mars reaches what’s known as a stationary point.

After this Mars will appear to move west until it reaches its next stationary point in mid-November. In reality, Mars hasn’t changed direction at all, the effect is simply a consequence of Earth’s own orbital motion relative to that of Mars.

Mars and the Moon will appear close together in the night sky around 11pm BST from the UK. Credit: Stellarium
Mars and the Moon will appear close together in the night sky around 11pm BST on 5 September. Credit: Stellarium

The size of Mars increases dramatically this month too. On 1 September a telescope shows the planet to have an apparent size of 18 arcseconds. By the time 30 September has come around, Mars will have grown to appear 22 arcseconds across; a 22% increase in size.

The planet’s increase in brightness is just as dramatic, Mars brightening from mag. –1.8 on 1 September to mag. –2.5 by the month’s end. Mid-month, Mars overtakes Jupiter in the brightness stakes to become the second brightest planet in the sky after Venus.

Over the remainder of the night and into the morning of 6 September, the separation continues to get smaller. It reaches a minimum value of half a degree around 06:30 BST (05:30 UT) under daylight conditions.

With Mars being so bright at this time, it should be easy to follow the pair with binoculars or a telescope despite the Sun being up.

The phase and relative sizes of the planets in September 2020. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence
The phase and relative sizes of the planets in September 2020. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence

How to see the planets this month

Mars

  • Best time to see 30 September, 02:00 BST (01:00 UT)
  • Altitude 43˚
  • Location Pisces
  • Direction South
  • Features Dark ‘albedo’ features, polar caps, weather
  • Recommended equipment 150mm or larger

Venus

  • Best time to see 14 September, from 04:00 BST (03:00 UT)
  • Altitude 10˚
  • Location Cancer
  • Direction East

Venus is a morning planet and well positioned all month, rising four hours before the Sun. Its phase and size changes dramatically when viewed through a scope in September. On 1 September, shining at mag. –4.1, Venus presents a 19 arcsecond disc, 59%-lit. By the month’s end, having dimmed to mag. –4.0, Venus presents a 15 arcsecond disc, 71%-lit.

14 September is the best time to see the planet visually, as this is when Venus and a slender crescent Moon sit either side of the Beehive Cluster.

Jupiter

  • Best time to see 1 September, 21:30 BST (20:30 UT)
  • Altitude 14˚
  • Location Sagittarius
  • Direction South

Jupiter is an evening object, reaching its highest position as darkness begins to set in at the month’s start. It remains low and is joined by Saturn to the east. On 1 September Jupiter shines at mag. –2.4, dropping to mag. –2.2 by the month’s end. A gibbous Moon sits near to Jupiter and Saturn on the evenings of the 24th and 25th.

Saturn

  • Best time to see 1 August, 00:30 BST (23:30 UT)
  • Altitude 16˚
  • Location Sagittarius
  • Direction South

Saturn appears east of Jupiter, the pair being 7.4˚ apart on 30 September. It appears low from the UK, only managing to attain an altitude of 16˚ when due south. Saturn fades this month, from mag. +0.6 on the 1st to +0.8 on the 30th.

Through an eyepiece, its rings remain well presented, the northern pole tilted towards Earth by nearly 23˚. A waxing gibbous Moon sits 3.2˚ south on the evening of 25 September.

Uranus

  • Best time to see 30 September, 03:00 BST (04:00 UT)
  • Altitude 51˚
  • Location Aries
  • Direction South

Uranus is well positioned this month, located in the southern part of Aries and not too far from Mars. It shines at mag. +5.7, making it theoretically visible to the naked eye from a dark-sky site.

One problem with this is identifying where Uranus is as this area of sky is bereft of any easy to use navigational patterns. Binoculars are a sure way to see it, as is the use of a scope. Even a small aperture should reveal its green hue.

Neptune

  • Best time to see 11 September, 01:10 BST (00:10 UT)
  • Altitude 32˚
  • Location Aquarius
  • Direction South

Neptune reaches opposition on 11 September when it can be seen in darkness all night long, shining at mag. +7.8, 2.1˚ east-northeast of mag. +4.2 Phi (ϕ) Aquarii. Opposition makes little difference to distant Neptune’s appearance in a scope, in contrast to a closer body such as Mars.

Being below the threshold of naked-eye visibility, you’ll need at least a pair of binoculars to spot it. A scope will reveal the planet’s blue-coloured disc.

Mercury

Mercury is not visible this month.

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Pete Lawrence is an experienced astronomer and a co-host of The Sky at Night. This article originally appeared in the September issue of BBC Sky at Night Magazine.