Stargazing June: Resplendent Saturn and its moons will bring drama and colour to the skies

Later this month the ringed planet will be at its closest point to us, but other planets in the solar system

Saturn is girdled by brilliant appendages that would stretch almost all the way from the Earth to the Moon (Nasa)

Time for another planet this month: in June, it’s ringworld Saturn’s turn to shine. Look very low in the south – just to the left of Scorpius – and you’ll spot this creamy yellow gem of the skies amongst the packed stars in the constellation of Sagittarius.

On 27 June, it is at “opposition” – opposite the Sun in the heavens, and closest to Earth. Saturn is a “mere” 1,354 million kilometres away! Before William Herschel’s discovery of Uranus in 1781, it was the most remote planet known in our solar system.

Last September in this column, we followed the self-destruction of the space probe Cassini, which had been a constant companion of Saturn since 2004. The discoveries of potential life-supporting conditions on two of the planet’s 62 moons – Titan and Enceladus – prompted Nasa scientists to destroy the probe. After running out of fuel, they couldn’t afford to have the probe collide with either moon, and wreak biological contamination on any living habitats.

Now is the time to grab a small telescope and take a look at this unique planet, resplendent at its closest. It looks like something out of the old cartoons of Dan Dare in The Eagle magazine – where all planets were depicted as having rings. Saturn is girdled by brilliant appendages that would stretch almost all the way from the Earth to the Moon. Through a telescope the planet – honestly – looks like a filmset model. You can’t believe that it’s real.

Galileo – first to spot the rings in around 1610 – didn’t know what to make of them. His tiny, low-powered telescope showed them as two blobs on either side of the planet. It was left to Domenico Cassini to discover the real nature of the rings with a more powerful telescope in 1675.

Astronomers know that Saturn’s rings aren’t solid: they made of chunks of ice, ranging in size from snowballs to icebergs, racing around the planet like minuscule moons.

But nobody is sure why Saturn has this unique attraction. This planet was certainly born from icy lumps – it’s so far from the Sun that water would have been frozen solid out here. Perhaps the rings are just rubble left over from the planet’s construction.

Other astronomers think the rings were once part of an icy moon that got smashed up – either when it was hit by a wayward comet, or just because it strayed too close to Saturn and was ripped apart by the mighty planet’s gravity.

The night sky at around 11pm this month

But Saturn is not alone in having rings. Although none can compare to the glory of those circling Saturn, there are a surprising number of ringworlds in the solar system. Even the Earth may have briefly had a ring in the distant past, after the “big splash” impact that created the Moon.

But you’ll need a space probe to home in on the other ring systems. Jupiter-bound Voyager 1 discovered that the gas giant is circled by three very faint rings: they’re made of dust that has drifted off its moons Adrastea and Metis.

After Saturn, Uranus is the next planet out to be girdled by rings. It has 13; but they’re very thin, dark and faint. They’re thought to be very young on the cosmic timescale: around 600 million years old. The best guess is that they were created by collisions between former moons of Uranus.

Neptune has five skinny rings, which – like those circling Jupiter – are largely made of dust. And like the rings of Uranus, they seem to be made of debris blasted from collisions between long-gone moons.

And talking of moons: they have a vital role to play in keeping the rings of the outer planets in order. The gravity of tiny “shepherding moons” flanking the rings nuzzle their particles into place – acting as cosmic sheepdogs.

Maybe The Eagle was right after all!

What’s up?

This month, we can enjoy not just one Evening Star, but two – a pair of bright interlopers in the western twilight after sunset.

The more brilliant is Venus, blazing all month long and outshining all the stars. During the first half of June, it heads upwards past the twin stars of Gemini – Castor and Pollux – towards the faint constellation of Cancer (the Crab). Grab binoculars or a small telescope on 19 and 20 June to view Venus lying almost in front of the star cluster Praesepe (otherwise known as the Beehive).

During the second half of the month, we have a rare chance to spot the elusive planet Mercury. It lies the lower right of Venus, very close to the horizon – binoculars will help to reveal the planet that orbits closest to the Sun. On 27 June, you’ll find Mercury to the left of Castor and Pollux, shining rather more brightly than these stars.

Over on the other side of the sky, there’s a pair of giants. The king of the planets, Jupiter, shines low in the south in the constellation Libra (the Scales). And to its left, you’ll find the second largest planet, Saturn: as we’ve mentioned above, the ringworld is at its closest to Earth this month.

Stay up after midnight, and you’ll find Mars rising to the left of Saturn, heading towards a close encounter with Earth next month.

The reddish star between Jupiter and Saturn is Antares, marking the heart of the celestial scorpion, Scorpius. Above them, ancient astronomers assembled dozens of faint stars into a set of huge rambling constellations, marking out a Serpent Bearer (Ophiuchus), the Serpent he’s wrangling (Serpens) and the superhero Hercules. Unimpressive they may be, but this trio may rank among the oldest star patterns in the sky.

Diary

1 June, morning: Moon very near Saturn

3 June, morning: Moon near Mars

6 June 7.32pm: Moon at Last Quarter

13 June, 8.43pm: New Moon

16 June: Crescent Moon near Venus

18 June: Crescent Moon near Regulus

19 June: Venus very near Praesepe

20 June, 11.51am: Moon at First Quarter; Venus very near Praesepe

21 June, 11.07am: Summer Solstice; Moon near Spica

22 June: Moon near Spica

23 June: Moon near Jupiter

27 June: Saturn at opposition, very near the Moon

28 June, 5.53am: Full Moon

30 June: Moon near Mars

For the lowdown on all that’s up in the sky this year, check out Heather Couper and Nigel Henbest’s latest book ‘Philip’s 2018 Stargazing’