Vishu - The Astronomical New Year

First of all, Happy Vishu to all....Lets talk some astronomy on this eve.... We all know that from Earth, Sun would appear to revolve around us. The ancient people believed Sun actually is revolving around Earth in a circular orbit. To locate sun in its orbit, they divided the 'solar orbit' around Earth, called the ecliptic, into twelve equal parts. To identify these parts in sky, they joined some of the stars in that portion of sky to make out a picture. Then they named each part according to the picture they made out in that portion. These twelve parts of sky on the sun's path around earth are called the twelve Raashi's(രാശികള്‍), named Medam, Idavam, Midhunam etc. The strip of sky around Earth that comprises of these twelve raashis is called the Zodiac(രാശിചക്രം). See the picture below:


As Sun takes 365 days to make a complete revolution, it is trivial to see that it spends around 30 days (365 days/12) in a particular Raashi. Our Malayalam calendar is based on this concept. That is, our Medamaasam(മേടമാസം) is that period of the year during which Sun is in Medam raashi. The day on which Sun moves from one raashi to another is called Sankraanthi(സംക്രാന്തി).

Vishu is astronomically the Medasankraanthi(മേട സംക്രാന്തി), that is, the day on which Sun enters Medam raashi. Historically, Medam 1 is the beginning of Malayalam calendar. But most of us consider Chingam 1 as New Year which is the beginning of Kollavarsham(കൊല്ലവര്‍ഷം). This is believed to be started by the King of Kollam (Venad Udaya Marthanda Varma) who thought Chingam, the season of harvest, can be the beginning of a new year. Chingam has no astronomical significance. More on this topic can be found here , an interesting blogg by Vaishakhan Thampi,AASTRO office bearer and a research fellow in Physics  from NIIST,Trivandrum



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