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angular sizes of point sources - quiz

The Angular Sizes of Stars

optical image of star1 optical image of star2 optical image of star3

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).

optical image of HT Cas from Schmidt telescope

: arcseconds.

Click here if you cannot determine HT Cas' angular size from this image

A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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