A man looks up at the night sky and feels a sense of wonder as he takes in the sparkling spray of stars that fills the field of vision. No fool, he knows most of these twinkling points of light are distant stars much like the Sun, but perhaps tonight he hopes to see a particular feature of the night sky he has heard of on the news or a science show, or is thinking of taking up astronomy as an interest. After searching fruitlessly for some time, the would-be star gazer rubs the back of his aching neck and gives up, overwhelmed by the random confusion of the firmament. This is no surprise, for a person wanting to learn the secrets of the stars can no more do so by mere observation and luck than they could learn a foreign language by trying to read a novel written in French. Yet these secrets are easily unlocked by learning of the constellations.
Just as man has divided the land masses of the world into countries with imaginary borders, so he has divided up the night sky, into a total of 88 constellations. The study of the stars is a study as old as civilisation, and 48 of these constellations were known to the ancient world and named after the heroes of their mythologies: ‘…our ancestors’ association of the names of legendary figures with the configurations drawn by the stars…transformed a jumble of points into something easy and coherent to follow’ (“Navigating the Night Sky”, Guilherme de Almeida, Springer-Verlag, 2004, p51). Twelve of those 48 ‘ancient’ constellations will be known to anyone who consults their horoscopes as the signs of the zodiac, although it should be stressed that astronomers do not recognise astrology as a science, and the two fields should not be confused, even though they share certain terms of reference. Of the 88 constellations, only thirty-six can be seen from the northern hemisphere, with the remainder prominent in the southern hemisphere. Many of the ‘newer’ constellations are to be seen in the southern hemisphere, beyond the range of the scholars of the ancient world.
Contrary to popular belief, the scientific term ‘constellation’ does not refer to a pattern of stars. In fact, a constellation refers to an artificially demarcated section of sky containing a notable star pattern from which a constellation often takes its name. For example, the constellation of Gemini, relatively easy to locate in the night sky, not only contains the star pattern known as Gemini, but also other celestial bodies, most of which are invisible to the naked eye. The star pattern itself is known as an ‘asterism’. Anyone wishing to observe the asterism Gemini, or a deep space object within the greater constellation of Gemini, like the Eskimo Nebula, must first find the constellation, but this can be easily done.
According to Pamela Forey & Cecilia Fitzsimmons, ‘One of the easiest ways to find your way around the sky is to learn to recognise three or four constellations which serve as markers for all of the others’ (‘Stars and Planets’, Brockhampton Press, 2000, p28). Perhaps the most famous pattern in the sky is The Plough, also known as The Big Dipper, which most people can pick out without recourse to a star map. The Plough is actually part of a larger asterism called Ursa Major, from which the constellation Ursa Major takes its name. Therefore, to use the correct language, anyone wishing to view the asterism of The Plough should point their gaze (or binoculars, or telescope) in the direction of the constellation of Ursa Major.
Now that the star gazer has located Ursa Major, other points of interest can soon be found. Two stars, Merak and Dubhe, form an imaginary line at one end at one end of The Plough. If one heads upwards along this line, for around five times the distance between Merak and Dubhe, one will come across Polaris, the famous ‘north star.’ Polaris is the brightest star within the constellation of Ursa Minor and, with the aid of a star map, all the other visible stars within Ursa Minor can be identified. From Ursa Minor, one can find the neighbouring constellation of Draco and so forth, around the sky of the northern hemisphere. Such tracking becomes doubly crucial when one realises the constellations, like all celestial bodies, seem to move through our skies: ‘All the constellations will change in position as the Earth rotates during the night…These positions will change by about 15 degrees for each hour’ (2000, p29).
Night by night, a star gazer can record the progress of the constellations and whatever may be seen within them. Such records have been made for thousands of years, and have often proved useful from a historical prospective. For example, in November of the year 1572, ‘a new star’ was observed in the constellation of Cassiopeia, and among those who recorded its presence was Danish astronomer Tycho Brahe (1546 – 1601). This mysterious phenomenon faded from sight during 1574, but thanks to the notes made by the likes of Brahe, successive generations of scientists could search for signs of whatever had caused the ‘new star’. In the early 1950s, radio signals were detected within the appropriate region of Cassiopeia and through subsequent optical observations, the mystery was finally solved in 1962, when it was announced that what Brahe had observed was a supernova, the spectacular death of a star otherwise invisible to observers in the sixteenth century. Due to their diligence however, the remnant of the supernova could be located and observed in the modern age.
Constellations are therefore not just a method of identifying individual stars, but also of recording events that take place within their borders although, as Almeida points out, ‘This only means that the object in question is seen in that direction and does not mean in any way that it is related to the other stars in the constellation’ (2004, p52). Even stars apparently next to each other in an asterism may be totally unrelated in reality. ‘A constellation pattern has no real significance…This is well demonstrated by Alpha and Beta Centauri, which lie side-by-side in the sky, although in fact Alpha is 4.1 light years away and Beta is over 100 times more distant’ (Philip’s Astronomy Encyclopedia, general editor Sir Patrick Moore, BCA, 2002). This should not deter anyone from observing either star (or indeed any star), which can both be found within the constellation of Centaurus.
Constellations also come in useful when dealing with objects in motion, such as planets, which can be easily mistaken for stars by the unaided eye. Without constellations, one could no more look for a planet at night than one could find an unknown town by setting off in a car and hoping for the best. At the time of writing for instance (August 2012), Mars can be viewed in parts of the northern hemisphere, but without knowing exactly which part of the sky to look, locating the red planet would be a very difficult task. Similarly, comets can be tracked by observers (both amateur and professional) from Earth with the use of constellations, which assist in knowing where to point observational instruments, as was the case when monitoring comet Shoemaker-Levy 9 as it approached, and then smashed into, the planet Jupiter in July 1994.
As one cannot fully appreciate the geography of planet Earth merely by looking out of the window or reading an atlas, so it is with astronomy. The novice star gazer could do no better than by learning to identify a few simple constellations, and this, with the guidance of a star map, will make his experience of astronomy not only more beneficial in terms of learning, but also a great deal more enjoyable.
