Stargazing in February: Trying to catch clusters

Star clusters involve hundreds or even thousands of stars in close proximity, held together by the bonds of their gravitational pull, write Nigel Henbest

It’s called the Seven Sisters – but in reality there are hundreds of stars in the Pleiades (Nasa)

Go out for stargazing session on a dark night this month – well away from streetlights – and you’ll find that stars and the brilliant planet Jupiter aren’t the only sights on offer.

The glowing band of the Milky Way arches overhead. And, as your eyes grow used to the dark, you’ll also notice a handful of small fuzzy patches scattered around the heavens.

These are star clusters, where hundreds or even thousands of stars live in close proximity, held together by the bonds of their gravitational pull.

Just above Jupiter lies the brightest and best-known star cluster, the Pleiades. My favourite description of this gorgeous sky-sight comes not from an astronomer, but from the pen of the Victorian poet laureate, Alfred Tennyson. In his epic poem Locksley Hall, the Pleiades are “a swarm of fireflies tangled in a silver braid”.

This star cluster is also known as the Seven Sisters, but naked-eye skywatchers usually see any number of stars but seven! Like most people with moderate eyesight, I can pick out the six brightest stars; but keen-sighted observers can pick out eleven or more.

These are the most luminous members of a group comprising at least 1,000 stars, lying 440 light years away. The brightest stars in the Pleiades are hot and blue, and all the stars are young: astronomers estimate that they are less than a hundred million years old, as compared to almost 4,600 million years for the Sun.

Nearby in the sky, the Hyades star cluster is an older cousin to the Pleiades, dating back around 625 million years. More mature star clusters lack the zest of their younger cousins, as their original brilliant blue-white stars have died and left behind mainly their longer-lived yellow, orange and red siblings So the Hyades are more lack-lustre than the Seven Sisters, even though the cluster lies three times closer – near enough that its stars are clearly visible as individuals.

Dating back to Babylonian times, the stars of the Hyades have formed the head of Taurus (the Bull). Aldebaran, marking the Bull’s angry eye, looks as though it’s part of the Hyades, but in reality this red giant star just happens to be in the same direction, at less than half the distance.

Across the sky in Cancer you’ll find Praesepe, a more distant star cluster that appears as a faint patch of light to the naked eye. Its traditional western name means ‘the manger,’ with the blurry outline representing a loose bundle of hay. To ancient Chinese astronomers, this eerily glowing object was ‘the Exhalation of Piled-up Corpses’!

In 1609, Galileo turned the newly-invented telescope on Praesepe, and discovered it is in fact a cluster of faint stars. A magnificent sight through binoculars or a small telescope, the swarming appearance of its stars has led to its nickname the Beehive Cluster.

Praesepe is about the same age as the Hyades, and is moving in roughly the same direction through space. Most likely, these two clusters were born together, from the same natal cloud of gas and dust, and have gradually drifted apart on their long peregrination around our Galaxy.

When young, Praesepe and the Hyades together may have resembled the beautiful Double Cluster in Perseus – on the border with Cassiopeia – which are only 14 million years old. Just visible to the unaided eye, these near-twin star clusters – each covering an area the size of the Full Moon - are a gorgeous sight in binoculars or a small telescope. They are loaded with glorious young blue supergiant stars, with a sprinkling of red giants to add to their visual appeal.

Each of these clusters looks similar in brightness to Praesepe in our sky, but they are seriously dimmed by their distance – a staggering 7,500 light years. If the Double Cluster were as close to us as the Hyades, their brightest stars would rival Sirius and we would see a region of the sky the size of Orion crammed with a thousand celestial jewels.

What’s Up

The two brightest planets bookend these long February nights. After sunset, Jupiter is a beacon over to the west; you’ll find the Moon near the giant planet on 14 and 15 February. And Venus is rising in the south-east just before dawn, with the crescent Moon close by on the morning of 7 February.

On the evening of 16 February, the Moon passes just below the centre of the Pleiades, the Seven Sisters star cluster, hiding some of its fainter outlying stars.

The night sky at around 10pm this month (Nigel Henbest)

On the starry stage, Orion is ruling the heavens, aided and abetted by his two hunting dogs, Canis Major and Canis Minor. His companions include Castor and Pollux, the twin stars of Gemini; Capella, heading up the celestial charioteer (Auriga); and Taurus the bull, featuring red giant Aldebaran.

These "winter stars" are best seen at this time of year; they are lost below the horizon during the summer months. All the stars in the southern part of the sky, in fact, change with the seasons, as the Earth orbits around the Sun.

But we shouldn’t overlook the constellations to north, the circumpolar stars that are visible all year. Most familiar are the seven stars of the Plough, making up the body of the Great Bear, Ursa Major. Follow the two end stars of the Plough, and they lead you to the Pole Star, Polaris, which always lie due north. Between then twists Draco, the dragon who guards the polar regions. And you can’t miss the W-shape of Cassiopeia, seen by the ancient Greeks as a queen sitting on her throne.

Dairy

2 February, 11.18pm: Last Quarter Moon

7 February, early hours: Moon near Venus

9 February 10.59pm: New Moon

14 February: Moon near Jupiter

15 February: Moon near Jupiter

16 February, 3.53am: First Quarter Moon occults the Pleiades

20 February: Moon near Castor and Pollux

23 February: Moon near Regulus

24 February: Full Moon

28 February: Moon near Spica

Nigel Henbest’s latest book, ‘Stargazing 2024’ (Philip’s £6.99) is your monthly guide to everything that’s happening in the night sky this year