Sizing Them Up

The planets of the solar system appear to us as disks. Once we know a planet's distance from us, it is quite simple to measure the disk and translate that figure into a real measurement of the planet's size. But train your telescope on any star, and all you will see is a point of light. Pop in a higher-power eyepiece and guess what? It's still a point of light!

Only very recently (with the advent of the Hubble Space Telescope) have we been able to resolve the disks of any stars. In 1996, the HST took a picture of the star Betelgeuse. This image was the first resolved image of a star other than the sun. The Very Large Array has also been used to image Betelgeuse. Although far away (500 light-years), Betelgeuse is a red giant, and as we'll soon see, that means it has a very large radius.

The Very Large Array in Socorro, New Mexico, recently made an image of the nearby supergiant star Betelgeuse, the bright red star in the constellation Orion. Like the sun, Betelgeuse appears to send plumes of gas far above its optically visible atmosphere, as seen in this radio-frequency image.

(Image from NRAO)

7mm Radio Image of Betelgeuse's Atmosphere

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Court83y ol J. lim, C Carilll, S. M. Whits, A. J. Beasley, V R. G-. tfarson

Telescopes Mastery

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