Twinkle, Twinkle litte star..Why?

–Karthik Gurumurthy

Have you ever noticed how a coin at the bottom of a swimming pool seems to wobble? This occurs because the water in the pool bends the path of light reflected from the coin. Similarly, stars twinkle because their light has to pass through several miles of Earth’s atmosphere before reaching the eyes of an observer. It is as if we are looking at the universe from the bottom of a swimming pool. Our atmosphere is turbulent, with stream and eddies forming, churning and dispersing all the time. These disturbances act like lenses and prisms that shift a star’s light from side to side by minute amounts several times a second. For large objects such as the moon, these deviations average out. (Through a telescope with high magnification, however, the objects appear to shimmer. Stars, in contrast, are so far away that they effectively act as point sources, and the the light we see flickers in intensity as the incoming beams bend rapidly from side to side. Planets such as Mars, Venus and Jupiter, which appear to us as bright stars, are much closer to Earth and look like measurable disks through a telescope. Again, the twinkling from adjacent areas of the disk averages out, and we see little variation in the total light emanating from the planet.