The first method involves the precise electronic monitoring of a star when it is blocked out by the Moon. As the Moon makes its monthly orbital trek around Earth, it passes in front of many stars, but only occasionally are the stars bright enough for the detection equipment to complete the experiment. Although the technique is little more complicated than observing the length of time it takes for the star to disappear (which is almost instantaneous), it has revealed accurate diameters for several dozen stars.
However, the Moon's path is limited to a specific sector of the sky, and astronomers anxious to determine the sizes of other stars developed two exceedingly painstaking techniques—stellar interferometry and speckle interferometry—that ultimately required years of refinement to capture the diameters of a handful of stars. Both methods involve electronic analyses to cancel out the interference of the Earth's atmosphere and to take advantage of the physical properties of light propagation. To appreciate the difficult nature of these experiments, consider the fact that a typical star seen from Earth is about the same size as a walnut on the Empire State Building viewed from a distance of 600 kilometers, or as far away as Toronto.
The techniques of stellar interferometry, speckle interferometry and electronic monitoring of lunar occultations have produced the diameters of many of the stars in the Milky Way. The diameter of a star can also be inferred from stellar-evolution theory, based on the calibrations provided by the diameters of stars that have been measured. In this way, almost any star can now be tagged with an estimated diameter.
In tallying up the diameters, we find that among all the naked-eye stars, less than 1 percent are smaller than our Sun. And yet a census of all stars shows that the average star is both smaller and dimmer than the Sun. Thus the incongruity of the starry sky as seen from the backyard: It is the giants, the blazing beacons of the galaxy, that make up the familiar constellations. The average citizens of our starry vault make a
negligible contribution to the night sky.
