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The Angular Sizes of Stars
These are optical image of several stars, including the central star of HT
Cas, from the Schmidt telescope. Each
pixel in each image is 0.0005 degrees across. The stars themselves are
different sizes. You may think that a telescope gives a perfectly
magnified image of a far away object. In fact, telescopes are not perfect,
and the images from a telescope suffer from various distortions. The
distortions tend to spread out the light from a source. This is especially
important in the case of stars, which are so far away that they are
actually "point sources", with the light of the star coming from one point in
space.
An optical image of HT Cas is shown below. HT Cas is the star approximately
in the center of the image. The entire image is 0.01o
across (each pixel is approximately 1.8" across).
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