The Constellations

-By Rishi Shah and Suresh Bhattarai

Throughout human history and across many different cultures, extraordinary names from mythical fables have been associated with distinguished star patterns of various shapes and sizes. Known commonly as constellations, they are seen magnificently all over the night sky. The current 88 constellations as recognised by the apex institution, the International Astronomical Union (IAU), are based on what was historically suggested by veteran Greek-Egyptian mathematician-cum-astronomer Claudius Ptolemy (circa 90-168 AD).

He had propounded the geocentric model of the Solar System and eventually of the universe in 150 AD, which was accepted by the society until the heliocentric model was proposed by Polish astronomer Nicolous Copernicus in 1543. In about 500 AD, Indian mathematician and astronomer Aryabhatta had already divulged an ingenious notion of the heliocentric Solar System independently. Among the constellations, the 12 zodiac manifestations bear special significance both in horoscopic astrology and astronomy.

Zodiacus in Latin figuratively describes the quaint circle of animals. The creation of the zodiacal signs has been motivated by classical figures from the Greek zodiac that represents weird animals, people, tools and mythological hybrids. Furthermore, the constellations through which the Sun traverses within one year are called the zodiacal constellations


Fantasy picture

In colloquial usage, any constellation is a group of celestial bodies, usually observable stars which appear to form a unique fantasy picture in the sky. Astronomers today still utilise old expressions, though the new system focuses primarily on constellations as queer grid-like segments of the celestial sphere. However, in Hindu Vedic astronomy, the 12 constellations of the zodiac are called Raashis. These are exclusively divided into 27 Nakshatras or lunar houses.

In 1922 and 1930, Belgian astronomer Eugene Delporte aided the IAU in partitioning the celestial sphere into 88 constellations, clearly devising their final demarcations. These constellations share the names of their renowned Greco-Roman predecessors, like Auriga (charioteer), Andromeda (chained princess), Orion (hunter), Leo (lion) and Scorpius (scorpion). While such formations were originally linked to mystical events, creatures, devices or persons, the categorisation of the night sky into recognisable displays was important on land and for sea navigation prior to the invention of the compass.

The division of the ecliptic into zodiacal representations allocated with particular stars had presumably originated from Babylonians (who inhabited Mesopotamia that is Iraq today) during the first millennium BC. The ecliptic is the apparent path that the Sun takes in the sky as it seemingly travels on an imaginary celestial sphere in one year. Zodiacal postulation was expounded also in the holy Rigveda roughly in 1700-1100 BC. The ecliptic was then cleaved into 12 equal zones of celestial longitude to create the first known celestial coordinate system, which is ostensibly advantageous over the modern equatorial or ecliptic coordinate system.

The Babylonian calendar assigns each month to a constellation that begins with the Sun’s position at the vernal equinox, which had dwelled then in Aries (ram). Consequently, it was dubbed the Age of Aries. For this reason, the first astrological symbol is Aries even after the vernal equinox has drifted away from Aries and lies presently in Pisces (fishes) due to the precession of the earth.

Popularly identified as precession of the equinoxes (because the equinoxes advance westward along the ecliptic relative to the fixed stars, opposite to the solar motion along the ecliptic), precession of the earth denotes a gravity-induced gradual shift in the orientation of the earth’s axis of rotation, mimicking the wobbling top that traces out a cone, which requires approximately 26,000 years to complete one cycle.

Greek astronomer and mathematician Hipparchus (190-120 BC) is credited for its discovery. As the earth revolves around the Sun, it arrives at two opposite points that are designated vernal and autumnal equinox from where the tilt of its axis (generally twenty three and half degrees to the perpendicular) is neither away from nor towards the Sun, and the Sun hovers vertically above the equator. They occur on March 20 and September 23 this year (2010). The duration of the night and day are almost equal worldwide on these days. If visualised from the earth’s perspective, at equinox, the Sun is at one of these two opposite equinoctial points on the celestial sphere where the celestial equator and ecliptic intersect.

In modern astronomy, a zodiac is a spherical celestial coordinate system. It characterises the ecliptic as its fundamental plane and the position of the Sun at vernal equinox peculiarly as its prime meridian. Since there are merely 365 and one fourth days in one year and 360 degrees in a circle, the Sun is allegedly gliding gracefully along the ecliptic plane at a rate of slightly less than one degree per day.

Traditionally, there were 12 zodiac constellations which were being used by astrologers. These zodiac constellations were separated by exotic boundaries that were adopted from antiquity. Now they have been redefined by astronomers in such a way that the Sun journeys quirkily through 13 constellations annually. The controversial 13th zodiac constellation is the famed Ophiuchus (serpent bearer) that is not embraced as one of the conventional zodiac constellations, even though the Sun spends a substantial amount of time from December 1 to December 19 each year comfortably in Ophiuchus.

The sprawling Ophiuchus alias Aesculapius was the legendry first doctor of medicine that encompasses the Serpens Caput (snake’s head) and Serpens Cauda (snake’s tail). Although the principal northern portion stays above the ecliptic, Ophiuchus’ southern part actually crosses it. The enchanting Scorpius stretches curiously below its feet as well as below the ecliptic.

The stellar arrangement that is not classed as a constellation is referred to as asterism, but nonetheless they are widely recognised by the astronomy community. Some obvious examples of asterisms include the exquisite circlet of Pisces, seven bright stars in the Ursa Major (great bear) known as Saptarsi locally or the Big Dipper or Plough elsewhere, and the large alluring summer triangle that is sketched by the resplendent stars Altair (Sravana), Deneb and Vega (Avijit) and could be viewed in the summer night sky fascinatingly in the Northern Hemisphere. These stars belong to the confounding constellations Aquila (eagle), Cygnus (swan) and Lyra (harp).

Whilst a grouping of stars may be officially labelled a constellation by the IAU, this does not unequivocally say that stars located in that constellation are necessarily gathered together in space. Sometimes they are apparently discerned near to each other, like the awe-inspiring Pleiades (Seven Sisters) that resides bewitchingly in the zodiacal constellation Taurus (bull). They are our bewildering interpretation of two dimensional images made up of stars with varying luminosity and differing distances.

Simple planetarium

To understand the Solar System, zodiac and equinoxes with the movements of the earth, moon, planets and other cosmic entities, the human orrey should prove to be one of the best instruments. It could effectively demonstrate astronomical concepts in a precise manner. The key features of the orbits of the heavenly objects are logically elucidated on the ground in great detail. The human orrey could be further considered as a simple planetarium on a modest ground.

Sky-enthusiasts especially school students and younger generation could play the role of the moving planets and comprehend the existence of our universe and the baffling evolution of lives on our blue planet earth through mind-boggling games and educative activities.


Source: The Rising Nepal, National English Daily,February 24,2010