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Atmospheric seeing

Written by: Annarien Bester, SALT intern

If you look with your naked eye at the night sky, you will see twinkling objects, most being stars. This twinkling is caused by atmospheric disturbances in the earth’s atmosphere. The higher the disturbance, the more the light from a star is blurred, and the image we observe looks ‘fluffier’. This is called atmospheric seeing. The lower the atmospheric seeing, the more stable the atmosphere is. Low atmospheric seeing results in a higher concentration of light from an object being observed.  In simple terms we can see a star as a point source when the atmosphere is stable with a low atmospheric seeing value and not a fuzzy, twinkling object.

The Hubble Telescope has the advantage of being situated outside the earth’s atmosphere and has an atmospheric seeing of 0, which is why Hubble is able to take such ‘sharp’ images.

Image Credit: Alan Adler took these photos which show the double star Zeta Aquaril to show how atmospheric seeing distorts the light from an object. The far left shows good seeing, the far right is an example of poor seeing. Source:

Read more about “seeing” in the article: “Twinkle, twinkle little star”.