Radio serial on astronomy
Episode 4: Pattern in stars
[Note for script writer: This brief has been prepared keeping the average non-specialist viewer in
mind. The attempt has been to develop the subject in a logical sequence that could bring out the
excitement of the process of making new discoveries and relating them to the gradual understanding
of the nature of the Universe. It is not designed to be a popular account of the development of
astronomy as a scientific discipline and its impact on our understanding of the cosmos. Since the
treatment is not rigorous, many details are not included. The script has to be developed along the
outline suggested using simple colloquial language as far as possible. The dialogues and
conversations need to be lively without any suggestion of pedagogy.]
Points to be covered:
- The Sumerian origin of constellations
- Early constellations
- Ptolemy’s work
- Polar constellations, Pole Star as navigation aid
Outline of content:
If we look at the clear sky on a dark, moonless night, the view can be bewildering. The number of
stars that we can see seems countless. Trying to make any sense of it appears almost impossible. So
it was, till about 2,000 B.C., when seafaring people who lived on the coast of the Mediterranean
grouped the brighter stars into various patterns called constellations to help them navigate at night in
the sea or in deserts. They could imagine familiar objects outlined by prominent stars; much like a
child of today makes up hidden figures by joining up the dots in puzzle books.
Ancient records in the form of prehistoric seals, vases and stone tablets suggest that the constellations
may have had their origin as early as 4,000 B.C. The oldest astronomical cuneiform texts, from the
second half of the 2nd millennium BC, record the Sumerian names of the constellations still known as
‘the lion’, ‘the bull’, and ‘the scorpion’. Old engravings suggesting shapes of the scorpion, lion,
hunter (Orion) and the big dipper have also been discovered in China.
The constellations we know today have been derived from a group of 48 known to the ancient Greeks
and listed by the 2nd century Greek astronomer Ptolemy in his astronomical work Almagest. These
constellations were given names of animals or objects with which early civilizations were familiar.
So we have Aries (the Ram), Taurus (the Bull), Leo (the Lion), Pisces (the Fishes), Libra (the Scale)
and so on. Some constellations were named after Greek or Roman mythological characters such as
Andromeda, Cepheus, Hercules, Pegasus and so on. There were also interesting mythological stories
associated with some of the constellations, which formed the lead characters in those stories. In some
cases, different civilizations had different names for the same set of stars. For example, in the
northern constellation of Ursa Major, the pattern of seven stars forming the tail of the mythical bear is
known as the “Big Dipper” in the West, but in India the seven stars represents seven sages and the
asterism is known as “Saptarshi Mandal”.
Although the constellations have been different names, only a few of them really resemble the objects
they are named after; in case of the others there appears to be no logic behind the names. For example,
the outlines of the constellations of Scorpius, Leo, and Cygnus indeed look like a scorpion, lion and
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Radio serial on astronomy
flying swan respectively. But if you try to look for ram in Aries, or crab in Cancer, or a eagle in
Aquila then you would be greatly disappointed.
We should also keep in mind that the constellations are not real things. The stars that make up a
constellation usually have no physical connection between one another, nor are they fixed in space.
Although they appear in the same direction in the sky, they are actually at vastly differing distances
from us. Some of the stars may be as much as 10 to 12 times as far away from us as another in the
same constellation. They appear as part of the same constellation only because they lie in our line of
sight as we look at them from Earth. This is like looking at a group of trees from distance. From far
away the trees appear to be arranged in a dense row. But if we go near we find that the trees are
scattered randomly with large spaces between them.
An interesting outcome of using the constellations as direction finders at sea was the discovery of new
constellations not visible from the northern hemisphere, something our ancestors may not ever have
imagined. The new discoveries provided the earliest evidence that the Earth is shaped like a sphere. It
was because of the spherical shape of the Earth that constellations visible from the southern
hemisphere always lay below the southern horizon when seen from the north.
For this reason, the visibility of different constellations depends on not only the position of the
constellation in the sky, but also where you are on Earth. If you live somewhere in northern India – in
Delhi or Jammu, for example – you will not be able to see some southern constellations such as Crux,
or Centaur. But the same constellations can be seen from places like Bangalore, Chennai and
Kanyakumari, which are nearer to the equator. On the other hand from Kanyakumari, Big Dipper or
Saptarshi Mandal and Cassiopeia will be seen very low over the northern horizon and the Pole Star
will be hardly visible. But from here Scorpius will be seen high up in the southern sky.
As many as twelve constellations of the southern sky, not visible from northern hemisphere, were
discovered in the 16th century. Other constellations were subsequently added to the list. Today, a
total of 88 constellations, into which the entire sky is divided, are recognised by the International
Astronomical Union. But out of the 88 only a few constellations are prominent and can be recognised
easily. Twelve of the constellations are seen along the ecliptic, which marks the apparent path of the
Sun in the sky. These 12 constellations are called the ‘zodiacal constellations’. They are important
because the Sun, Moon, and the planets are seen in the sky only in the background of these
constellations.
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