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“Seeing”

Notes:

Now we will move onto the next problem with observing. It goes by the jargon term “seeing”. This slide will define that term.

Let’s say that you are interested in looking at a double star. In principle, a double star should be two point sources of light located very close to each other (within Arc Seconds for some). Leaving optics issues aside you should be able to resolve these into two separate sources of light. This is shown in the upper left drawing.

The next night you attempt to observe the same double star with the same telescope from the same site. All you see is a dancing mush. What happened?

The large Dob telescopes should be able to view an image of Jupiter that is almost as good as the Hubble image in the lower left. Yet on many nights Jupiter looks like the image on the lower right.

The answer was the “seeing” was good in the images on the left and poor in the images on the right.

Seeing is quantified in arcseconds. This is related to how much detail can be resolved on a particular night.