Simple Stargazing

As we’ve seen with the Plough and Crux, several distinctively shaped and therefore easily recognisable constellations – or parts or combinations of constellations – make useful ‘signposts’ around the night sky. These can be used to find all manner of starry splendours, so I will point them out as we go.

Here’s a rough map of the planet that I knocked together using a plastic washing-up-liquid bottle, some sticky-backed plastic and an old coathanger. The equator divides the world into a northern and a southern hemisphere, which is your cue to choosing which of the seasonal charts to look at. The nearer to the equator you travel, the more of the opposite hemisphere’s chart you can use. For example, if you live somewhere in Norway, you’ll be using just the northern chart. If one summer you decide to go on holiday to Italy, you can use half of the southern chart with all its fascinating new starry sights.

The sections have also been divided into those for northerly people and those for southerly, because exactly what you’ll see depends on whereabouts on our planet you live. If you’re well into the northern hemisphere (the bit above the equator on the map) then go for the northern charts, while if you’re in the southern… well, you get the idea. As most of the land – and the majority of the world’s population – is in the northern hemisphere, the charts appear as if you are looking south. The closer to the equator you are in the northern hemisphere, the more of the southern chart you can use. For those lucky souls who live on the equator, the whole sky is visible and you can use both charts at once.

Each constellation of interest is introduced with the following useful information:

LATIN NAME

Ursa Major

ENGLISH NAME

The Great Bear

ABBREVIATION

UMa

LATIN POSSESSIVE

Ursae Majoris

α STAR

Dubhe

MAGNITUDE

1.79

STAR COLOUR

Orange

First, you’ll find the constellation names in the original Latin, and then the English equivalent. The following three-lettered abbreviation is an internationally recognised way of identifying a constellation without having to use its full name.

The Latin possessive means ‘of the constellation’ or ‘belonging to’. This is used for sounding important and as if you know what you’re talking about – something like: ‘Oh, Castor. Of course you mean alpha Geminorum.’

The alpha (a) star is the main star of the named constellation, though it is not always the brightest and not all constellations have alpha stars with names (or even alpha stars at all). In 1603 the German astronomer Johann Bayer worked through each constellation, usually assigning alpha (a) to the brightest star, beta (β) to the next brightest, then gamma (γ), delta (δ) and so on. As a result, stars are often labelled on charts with a letter of the Greek alphabet, known as the Bayer Letter. The full Greek alphabet is given on the right.

Proper names, such as Dubhe, are only generally given to the brighter stars. Many of the names are Arabic, but there are splatterings of Greek and Roman ones too. Check out the constellation Libra (see Libra) for the best star names in the Universe.

Star magnitude (mag.), or ‘visual magnitude’, lets you know how bright a star appears in the sky. The Greek astronomer Hipparchus, who lived around the mid-second century BC, introduced the system of classifying starry magnitudes that you can see with your eye from 1, the brightest, down to 6, the faintest. We’ll be talking more about magnitude in just a moment or two, and as you will see, it’s now a little more complicated.

As well as the colour of a star indicating the obvious, it can also tell you how hot its surface is. You may be surprised to learn that the coolest stars are red, their surfaces being about 3,000°C. Warmer stars are yellow, the hotter ones white and the hottest are blue, with temperatures up to 40,000°C. Not only that, but they can change colour! This most notably happens when stars have used up all their fuel and internal forces take over, causing all manner of starry events (like red giants, supernovae and black holes, for example).

Greek alphabet

Bright or Dim?

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