B S Shylaja is with the Bangalore Association for Science Education, which administers the Jawaharlal Nehru Planetarium as well as a Science Centre. After obtaining her PhD on Wolf-Rayet stars from the Indian Institute of Astrophysics, she continued research on novae, peculiar stars and comets. She is also actively engaged in teaching and writing essays on scientific topics to reach students.

The twinkling diamonds in the night sky make us wonder at their variety – while some are bright, some are faint; some are blue and red. The attempt to understand this vast variety eventually led to the physics of the structure of the stars.

The brightness of a star is measured in magnitudes. Hipparchus, a Greek astronomer who lived a hundred and fifty years before Christ, devised the magnitude system that is still in use today for the measurement of the brightness of stars (and other celestial bodies). Since the response of the human eye is logarithmic rather than linear in nature, the system of magnitudes based on visual estimates is on a logarithmic scale (Box 1). This scale was put on a quantitative basis by N R Pogson (he was the Director of Madras Observatory) more than 150 years ago.

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Address for Correspondence
B S Shylaja
Bangalore Association for
Science Education
Jawaharlal Nehru Planetarium
Bangalore 560 001, India.
Email: taralaya@vsnl.com