October 13, 2014

Pictures in the Sky

Ian Ridpath

Report by: Andy Sawers

Ian Ridpath

Ian Ridpath gave a lecture to the Flamsteed Astronomy Society on 13 October 2014. Andy Sawers summarises his fascinating talk.

Making pictures and patterns out of the stars is the ultimate game of ‘Connect the dots’ – but where did the constellations we know today come from? This was the theme of the talk to Flamsteed members in October by Ian Ridpath, an author, broadcaster and lecturer on astronomy who has more than 40 book titles to his name.

There were two main parts to Ian’s talk: the ancient constellations which have their roots over 3,000 years ago in the Middle East and the newer constellations, predominantly those added since the 16^th century by the European explorers as they sailed into southern oceans.

Which came first?

We all know that many of the constellations have stories attached to them – but which came first? The constellations or the stories? Ian believes that stories had been handed down through the oral tradition for generations – stories about gods, mythical heroes and fabulous beasts. And to ‘illustrate’ them the storytellers used the stars, tracing out pictures in the sky. And so the first constellations came into being, like pictures in a book. Perhaps that’s one reason why the imagined patterns don’t really look much like the characters they are supposed to represent. Leo may look like a lion but Cassiopeia doesn’t look much like a woman sitting in a chair, combing her hair. But as Ian said, “The original constellations weren’t intended to be taken as literal representations, simply allegorical.”

Other cultures saw completely pictures, though the Chinese had a constellation we’d all recognise called The Northern Dipper.

A few constellations from Greek literature date back to around 700BC with the works of Homer and Hesiod – eg, Great Bear, Orion, the Pleiades star cluster, and Sirius – but it’s not until around 350BC that we see a more complete set of Greek constellations, produced by Eudoxus. His work has long since been lost but it lives on in a poem called Phaenomena by Aratus.

However, as we shall see later, the constellations may not be of Greek origin.

Ian Ridpath during his talk to the Flamsteed

Back-to-front pictures

The oldest known pictures of these constellations comes from a Roman copy of a Greek statue of Atlas holding not the earth but the heavens – the oldest known celestial globe, known as the Farnese Atlas because it was bought by an Italian cardinal of that name.

Being a globe, everything is back-to-front by comparison with the way we see the constellations from earth. And of course in the area around Atlas’s head there are no constellations because that’s the area around the south pole that couldn’t be seen from the Mediterranean. But for the most part they are the constellations that we still recognise today.

For a scientific description of the Greek constellations we turn to Ptolemy, a Greek scientist working Egypt who around AD 150 wrote The Almagest. It contains a catalogue of about 1,000 stars and 48 constellations. Surprisingly (at least to the modern reader), The Almagest lists the coordinates and the magnitudes of the stars, grouped according to the constellation they’re in. But the stars themselves have no names, just descriptions: eg, “the reddish one on the southern eye” (the star we know today as Aldebaran – an Arabic name that came later) or “The bright reddish star on the right shoulder” (now known as Betelgeuse, also from the Arabic).

Eight hundred years go by as the centre of astronomy moves from the Greeks to the Middle East . The Persian astronomer Al-Sufi wrote The Book of Fixed stars, an updated version of The Almagest with exactly the same 48 Greek constellations. It was beautifully illustrated and showed the constellations two ways: as seen on a celestial globe and as seen from Earth. He is also said to be the first to specifically note the Andromeda galaxy: even though it’s a naked eye object there is no record of it in any of the Greeks’ writings.

Through the Middle Ages the Arab empire expanded across North Africa and into Spain, re-introducing the Greek works into Western Europe from the 11^th century onwards. The Spanish city of Toledo became virtually a translation factory in the 12^th century.

As for the names of the stars, a lot of them come from Arabic. As we’ve seen, most stars didn’t have Greek names so the Arabic name survives to this day.

The sky in print

Things start to develop quickly with the invention of printing, making it so much easier to create multiple copies of books and maps without having to laboriously copy by hand or make celestial globes or astrolabes.

The first noteworthy printed celestial chart was drawn by the German artist Albrecht Dürer. But the constellations were shown back to front, as they appear on a celestial globe. Because people were used to seeing figures on a globe, many early maps continued to show them that way round. Eventually it dawned on map-makers that it’s more sensible to turn them the right way round as we see them from earth.

From the empty space in his southern hemisphere chart we can tell that the people who invented the constellations lived around 36 degrees north. That’s too far south for the Greeks. So if the Greeks didn’t invent the constellations, who did?

The first constellations probably had their origins about 3,000 years ago in the Middle East among the Sumerians in Mesopotamia. Somehow, their knowledge reached the Greeks who incorporated their own myths into it and catalogued the stars. So although they didn’t invent these constellations they embraced them and made them their own.

Ian takes questions from the audience

The new constellations

The first new constellations for over 1400 years were introduced when Europeans started setting sail around the world. Petrus Plancius (“Peter Flatfoot”) was a Dutch cartographer who, with Pieter Dirkszoon Keyser, sailed to the East Indies and produced a catalogue of southern stars that was divided into 12 new constellations which first appeared on a celestial globe by Plancius in 1598. “The thrill of getting the first southern star catalogue must have been like getting the first pictures of the far side of the moon,” Ian said. “It was a part of space that had never been seen before.”

The German Johann Bayer labelled stars with Greek letters. They are now usually known as Bayer letters and were a great improvement over Ptolemy’s long-winded descriptions.

Later in the 17^th century another group of constellations introduced by Polish astronomer Johannes Hevelius produced a star atlas introducing seven new constellations including Sextans, Lynx (he said you’d have to be lynx-eyed to see it because the stars are so faint) and Scutum, which represents shield of the king of Poland – the only constellation introduced for political purposes that still exists.

The Frenchman Nicolas Louis de Lacaille went to South Africa in 1750 to make a catalogue of 10,000 stars and introduced 14 new constellations, many named after instruments from the science and the arts such as Antlia (the air pump) and Telescopium.

The pinnacle of the celestial mapmaker’s art, however, was Johann Bode’s Uranographia in 1801, with around 100 constellations – a dozen more than today.

The modern list

At the first meeting of the International Astronomical Union in 1922 it adopted the list of 88 constellations we know today. But it didn’t set the boundaries between them. Some constellations overlapped and some stars were shared by constellations – the star at the right foot of the Charioteer was also in Taurus.

It commissioned Eugene Delporte to divide up areas of the sky into the 88 constellations, defining them by right ascension and declination (celestial longitude and latitude). He presented his atlas in 1930. “There were no pictures – they were too frivolous. So when astronomers say a star is ‘in’ a constellation they mean it’s in that area of sky rather than forming part of the picture,” Ian said. But as a result, star charts were a confusing mass of dots. So now the main stars are often joined up by lines which actually have no official status – and vary from map to map – but are helpful in identifying the major patterns.

Ian’s parting thought: the old patterns won’t last forever because all stars are moving. He showed how different the plough will be in 100,000 years

“Constellations aren’t just about the stars,” he said. “They’re about poetry and art and above all human imagination and they give us a very real connection with the earliest civilisations who looked up and imagined those first pictures in the sky.”

The Flamsteed Q&A

There were some great Flamsteed member questions on whether we should start preparing now for the new constellations we’ll have as the stars move (“Why not – and in any event, don’t be hidebound by the existing constellations if you see shapes that help you navigate around the sky”), the drift of dim and distant stars from one constellation to another (“At that level they’re named by star catalogue numbers, not by the constellation they’re in”), the Babylonians’ naming of constellations (“Not my area – I start with the ancient Greeks”), what Orion will look like in 100,000 years (“Don’t know – there’s some homework for you!”), whether constellation Sextans was named before the instrument was invented (“Not to be confused with a reflecting sextant – it was named after an astronomical instrument rather than a navigational sextant”), why the different languages – Arabic star names, Greek constellations – survived the journey and the translation into Latin. (“For whatever reason, they stuck!”)

Ian’s Star Tales website has a wealth of information and illustrations – it is well worth visiting!