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We are all familiar with the mythological story of the three steps that Vishnu took, in His avatar as Vamana. His first step covered the earth, the second the sky and the third was on King Mahabali’s unfortunate head! Interestingly this story is immortalized in stone in a temple in Kanchipuram. The deity there is called Ulagalanda Perumal, in Tamil, which translates as “the Lord who measured the world”! This bug, to measure the world, also bit humans. The human quest for measuring our universe is one of the most fascinating chapters in the history of science. A different type of observation is needed at every distance range. In each range, the distance measurement is used as a step in the ladder to measure distances in the next (larger) distance range. Collectively, these steps form the Cosmic Distance Ladder that reach out to the very edge of the known Universe. The distance from the earth to the sun, called the Astronomical Unit (A.U.), lies at the lowest rung of this ladder and is therefore a most fundamental measurement.
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