The stars that shine at night do so from immense distances.

In fact, stars are so remote that astronomers rarely use kilometres to express their distances. That's because even the brightest stars aren't millions or even billions of kilometres away, but trillions or quadrillions.

To avoid such cumbersome numbers, astronomers use a different unit of distance: the light-year. That is, the distance that light travels in one year. Since light travels fast, at 300,000 kilometres per second, even a single light-year is an immense distance; over 9,000,000,000,000 kilometres!!

The summer night sky is blessed with an abundance of bright stars. As a matter of fact, 8 of the 10 brightest stars in the whole sky are visible on summer nights.

Let’s begin our tour with Sirius, the brightest star in the night sky.
Sirius looks so bright for a couple of reasons. First, it really is bright; it produces about 30 times more energy than the Sun. And second, Sirius is less than nine light-years away. Only a few stars are closer.

Sirius is actually a binary, two stars that move through space together, bound by their mutual gravitational pull. The star that we see with the unaided eye is Sirius A. The other is Sirius B. Since Sirius is known as the Dog Star, Sirius B is nicknamed “the Pup.”

Sirius A is a main-sequence star. That means that like the Sun, it’s in the prime of life. Sirius B, on the other hand, is a white dwarf — the burned-out core of a once-normal star. It shines only by releasing the intense heat it built up during its long lifetime. It’s so small, and so close to Sirius A, that you need a telescope to see it.

Canopus, the second brightest star in the sky is located higher in the southeastern sky. Canopus is quite different from the Sun. It's a supergiant; many times bigger and heavier than the Sun. It's also more than 10,000 times brighter than the Sun, so it's easily visible across more than 300 light-years of space. It's nearing the end of its life, and within the next few million years should explode as a supernova. When that happens, Canopus will briefly outshine everything else in the sky except the Sun.

Hugging the southern sky at this time of the year is Alpha Centauri, the third brightest star in the sky, and our closest stellar neighbour, at a mere 4.25 light years. Arcturus, the fourth brightest and Vega, the fifth brightest are not visible at this time of the year. They illuminate the cold winter skies.

Sixth placed, yellow Capella hugs the northern horizon. Rigel and Betelguese, in Orion, are placed seventh and tenth respectively. In eighth place, Procyon, makes an appearance late in the evening in the eastern sky, whilst in ninth place, Achernar is almost overhead.

Of course, December is Christmas month, and if Santa is especially generous this year, you might find something shiny in your Christmas stocking: gold. As you admire it, think about this: that bit of soft, beautiful metal just might have been created during the birth of a black hole.

Almost all of the chemical elements are created by stars, either during their long lifetimes, or in supernovae; the explosive deaths of heavy stars. But some recent research says that some of the heaviest elements may require multiple stellar deaths.

These heavy elements, including gold, are the result of the merger of two neutron stars; the corpses of once-mighty stars that had already exploded. The collision forms a black hole. But the violent outburst that accompanies the merger blasts away some material before it can fall into the black hole. The ejected material includes some of the heaviest elements, which are difficult if not impossible to make in normal supernova outbursts. This includes a lot of gold. A typical merger could produce enough gold to make 10 Moons!

These kinds of mergers are rare, there’s probably only one every hundred thousand years in our own galaxy. But the researchers say that over cosmic time, they could account for all the gold in the universe.

If gold doesn’t feature on Christmas morning, perhaps a pair of binoculars will. These are a great way to develop your interest in astronomy. They will allow you to see many more stars, the craters on the Moon, the phases of Venus, the moons of Jupiter and many more of the vistas in our night sky. And what better target, than a group of stars known as the Pleiades.
Many people know them more commonly as the Seven Sisters. You can see them with the naked eye, as a small bright patch, about 20 degrees above the northeastern horizon. The Seven Sisters are a group of very young stars, perhaps no more than 6 million years old. (Our Sun is a middle aged star, at an age of approximately 4,500 million years old). Because they occupy an area of sky larger than the full moon, binoculars offer the best method of viewing these stellar siblings. Whilst seven is the number of stars you should be able to see with the naked eye under dark conditions, your view in binoculars will be rewarded by a sight of some 45 to 50 brilliant stars shining against the blackness of space. At 450 light years away, their light has travelled to Earth since the introduction of chocolate into Europe by the Spanish from Central America in the mid-1500’s.

Of course, I wouldn’t be forgiven if I didn’t mention brilliant Venus in the western sky after sunset. How could you miss it! It’s almost bright enough to cast shadows. Just remember that, whilst it may look alluring as it hangs in the orange pastel colours of late twilight, Venus is the closest we can get to our vision of Hell in the solar system. Venus is engulfed in a very dense atmosphere of carbon dioxide gas so thick that we can never directly see the surface. Because of this, heat accumulated during the day cannot escape at night, so temperatures on Venus are more than 600 degrees C all year round; hot enough to melt lead. And if that’s not enough, there’s a layer of sulphuric acid clouds in the atmosphere. Look for the thin crescent Moon and Venus in the evening twilight of December 4. See the sky diagram below.

Late on December evenings, there’s another planet also vying for your attention. Look low in the north-eastern sky, and the colossus of the solar system greets you. This is Jupiter, the largest of all the planets. If we could fill Jupiter with planets the size of the Earth, we would need over 1300 of them!

The Moon is New on the 1st of December, at First Quarter on the 9th, Full on the 15th, and at Last Quarter on the 23rd of December.