The brightest planets to see in August’s night sky

The Sky at Night's Pete Lawrence reveals how you can spot Mercury and the other planets in the night sky this month.

The planet Mercury will get brighter and easier to see in the morning sky throughout August 2019. Credit: Pete Lawrence

Although the planet Mercury isn’t particularly easy to see at the start of the month, its position does improve as time passes. By the time it reaches greatest western elongation on 9 August 2019, it rises approximately 100 minutes before the Sun.

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An elongation is the point in an inferior planet’s orbit when from Earth the planet appears at either the eastern or western extremity of its orbit (an inferior planet is one with an orbit smaller than Earth).

On 1 August 2019, Mercury will be approaching greatest western elongation. Through a telescope it will appear 9 arcseconds across and present a 13%-lit crescent.

Appearance of Mercury relative to the horizon at 05:20 BST (04:20 UT) during August 2019, as viewed from the centre of the UK. Credit: Pete Lawrence
Appearance of Mercury relative to the horizon at 05:20 BST (04:20 UT) during August 2019, as viewed from the centre of the UK. Credit: Pete Lawrence

How to see Mercury throughout August 2019

Best time to see: 9 August, 1 hour before sunrise 

Altitude: 5° (low)

Location: Gemini

Direction: East-northeast

Features: Phase, mottled surface features through larger telescopes or via imaging

Recommended equipment: A 75mm or larger telescope

It rises one hour before the Sun on 1 August and shines at mag. +2.0.

Mercury brightens quite rapidly as it approaches greatest western elongation and this, along with its increased apparent separation from the Sun, will make it much easier to see.

On 9 August it shines at mag. +0.3 and through a scope appears 37%-lit and 7 arcseconds across.

Although Mercury appears to get closer to the Sun after this date, its appearance in the morning sky actually improves. This is due to it becoming brighter and moving to the north of the ecliptic.

On 23 August Mercury appears at mag. –1.2, setting 70 minutes after the Sun.

Later in the month, despite being bright, its visibility will become hampered by its proximity to the Sun.

Mercury’s appearance through a scope tends to be compromised when it’s in either the evening or morning twilight because it’s always quite low.

Despite this its phase is quite evident and can be seen with a 75mm instrument at around 100x power.

Larger instruments may be able to reveal surface shadings if the seeing is good.

The phase and relative sizes of the planets in August 2019. 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 August 2019. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence

How to see the rest of the planets this month

Mars

Best time to see: 1 August, 20 minutes after sunset

Altitude: 0.75˚ (extremely low)

Location: Leo

Direction: West-northwest

Mars is all but lost from view this month. There is a thin Moon spotting opportunity on 1 August when it may be possible to see a less than 1%-lit waxing crescent in clear skies.

If you look for the Moon, mag. +1.8 Mars is located 0.8˚ south-southeast of its crescent shortly after sunset; that’s below and slightly left as seen from the UK.

On 24 August, Venus appears to pass Mars by 0.3˚, although the pair will only be 3˚ from the Sun.

Jupiter

Best time to see: 1 August, 22:30 BST (21:30 UT)

Altitude: 13.5˚

Location: Ophiuchus

Direction: South-southwest

Jupiter is showing a low aspect, a situation which will persist for another couple of years before it starts to climb to a more northern part of the ecliptic.

A side effect of its low altitude is that its period of observation is short, Jupiter appearing in dark skies for less than four hours.

A 72%-lit waxing gibbous Moon lies 1.5˚ north of mag. –2.2 Jupiter on the evening of 9 August.

On the evenings of 26 and 27 August Jupiter appears to pass in front of the globular cluster NGC 6235 – see page 47.

Saturn

Best time to see: 1 August, 23:40 BST (22:40 UT)

Altitude: 15˚

Location: Sagittarius

Direction: South

Mag. +0.5 Saturn is in Sagittarius moving slowly towards the west at the start of August, a movement which positions it under the bowl of the spoon in the Teaspoon asterism, which itself lies to the northeast of the Teapot asterism.

In the UK you’ll see a bright 88%-lit waxing gibbous Moon sit to the west of Saturn on 11 August and to its right on 12 August.

Saturn appears at its highest point in the sky, due south, in relative darkness all month long. It’s tilted over by 25˚ so that its northern pole is closer to Earth.

Uranus

Best time to see: 31 August, 03:45 BST (02:45 UT)

Altitude: 48˚

Location: Aries

Direction: South-southeast

As the nights begin to draw in, so the observing situation for mag. +5.7 Uranus improves.

At the end of the month, Uranus manages to reach its highest point in the sky, due south, in reasonable darkness.

The planet has drifted east out of Pisces and into neighbouring Aries. Its peak altitude as seen from the centre of the UK is 50˚, making distant Uranus the best placed planet currently on offer.

Neptune

Best time to see: 31 August, 01:45 BST (00:45 UT)

Altitude: 31˚

Location: Aquarius

Direction: South

Mag. +7.8 Neptune doesn’t make it to its highest position due south at the start of August but the lengthening nights and its drift westward means that it achieves this feat from around mid-month onwards.

Binoculars are required to spot Neptune, but a scope will show its distinct blue colour.

Neptune is in Aquarius, situated close to the mag. +4.2 star Phi Aquarii.

Venus is not visible this month

This article originally appeared in the August 2019 issue of BBC Sky at Night Magazine.

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Pete Lawrence is an experienced astronomer and a presenter on The Sky at Night.