Stargazing February: Look to the skies to see the Dog Star... and its Pup

Sirius, the brightest star in the sky and a younger and bigger sibling of our own Sun, will be much in evidence this month

Sirius is the jewel in the crown of Canis Major, one of Orion’s two hunting dogs (Getty)

Iconic Sirius is lording it over the southern skies this month. Sirius is the brightest star in the sky, but it’s not particularly luminous: it just happens to lie nearby on the cosmic scale – just 8.6 light years away.

Sirius is the jewel in the crown of Canis Major, one of Orion’s two hunting dogs. His main quarry is Orion’s adversary Taurus (the Bull), but in the sky he’s shown as chasing Lepus (the Hare). Popularly known as the Dog Star, the name Sirius derives from the ancient Greek Seirios, which means “scorcher”.

The Greeks believed that, as Sirius rose with the Sun in mid-July, its extra heat heralded the hot and humid “dog days”, when everything slowed down and dogs become lethargic. Worse was the fact that plants wilted, men weakened and women became – er – active!

And the bad omens attributed to Dog Star carried on over the winter. Twinkling low above the horizon, it was interpreted as flaming or burning. The Greeks thought that anyone looking at the star would be badly affected, and was said to be star-struck.

But the Greeks didn’t have it all their own way. It’s astonishing that – in many cultures around the world – Sirius has been associated with dogs. Roman farmers, for instance, sacrificed dogs when Sirius came close to the Sun in the sky in May.

To the Egyptians, the summer appearance of Sirius was good news. The annual “heliacal rising” (when Sirius rose just before the Sun) told them that the Nile was about to flood – a good harbinger for a bumper harvest.

In their lengthy voyages across the vast Pacific, the Polynesians used the star as a navigational beacon: Sirius passes directly overhead at Tahiti. In fact, it’s hard to name a civilisation that hasn’t relied on Sirius in one form or another.

Today, Sirius isn’t just a celestial beacon. Astronomers have sussed out its true nature, as a younger and bigger sibling of our own Sun. Sirius is a relatively young star: just 230 million years old, compared with the Sun’s venerable 4,600 million years. Boasting a temperature of about 10,000C, Sirius is twice as heavy as the Sun. And the Dog Star will shine even more brilliantly in our skies, not because it’s stoking up its fires but because Sirius is moving towards us. Prepare for maximum brightness – in 60,000 years’ time!

And Sirius isn’t a solo traveller through the Milky Way. In 1844, the German astronomer Friedrich Bessel noticed that Sirius was being pulled out of place by a faint companion star. This tiny sibling, nicknamed the Pup, was once a star much heavier than Sirius, but it has now puffed off its atmosphere to reveal the now-defunct central nuclear reactor.

To spot the Pup – which is 10,000 times fainter than Sirius – you’ll need a 150mm telescope, and good viewing conditions.

The same weight as the Sun, and yet the size of the Earth, the Pup is a dense white dwarf star – a fate that will eventually overtake our local star. It has a searing surface temperature of 25,000C and considerable gravitational powers. But it’s on the road to oblivion. With no nuclear reactions to keep it alive, the Pup will cool to become a dead, black globe. Just wait two billion years...

What’s up?

We’ve plenty of brilliant stars on display – but what you won’t see this month is a full moon. It takes 29½ days for the Moon to go through a complete cycle, so any month with 30 or 31 days must have at least one full moon. But February is short enough that it can miss out – something that happens every 20 years, on average. The last full moon fell on 31 January (the media hyped it as the supermoon, blue moon or blood moon) and we have to wait until 2 March for the next.

So make up by scanning the winter constellations. It’s easy to spot Orion the hunter, with seven stars making up the shape of his torso, with his two hunting dogs to the left and the mighty bull Taurus to his upper right, topped off with the lovely little star cluster of the Pleiades, or Seven Sisters.

High overhead soars brilliant Capella, along with the twin stars Castor and Pollux. To the left, you’ll find Leo, the lion, his heart marked by the blue-white star Regulus.

At the beginning of February, you’ll need to stay up till past the witching hour to bag any planets. Around 1am, brilliant Jupiter rises in the south-east, outshining even Sirius.

Mars rises a couple of hours later. The legendary Red Planet lies above one of the reddest bright stars in the sky, Antares. In Greek, the star’s name means “rival of Mars”, so take a look – preferably in binoculars, which bring out the colours – and decide for yourself which appears more red.

Finally, yellowish Saturn is rising about 5am.

Not a morning person? Just wait till the end of February, when Venus – the most brilliant planet – appears in the evening twilight on the western horizon. By the end of the month, the Evening Star is setting an hour after the Sun. And, if you have a clear low-lying horizon, you may just spot its fainter sibling, Mercury, lying to the lower right of Venus, some ten times fainter.

Diary

1 February: Moon very near Regulus

7 February, 7.47pm: Moon at Last Quarter

8 February, morning: Moon near Jupiter

9 February, morning: Moon near Mars

11 February, morning: Moon near Saturn

15 February, 9.05pm: New Moon, partial solar eclipse for South America and Antarctica (not visible from the UK)

23 February, 8.09am: Moon at First Quarter, and covers up Aldebaran

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’