what creates the "star points" in telescope pictures of stars?

Drakkith

You sure about that? Have you seen this picture? http://en.wikipedia.org/wiki/File:Be...8Hubble%29.jpg
It's from the Hubble Space Telescope in UV.

hipparchos

No. But we can determine its diameter using interferometry.

Drakkith

Does the image I linked above not prove otherwise?

Barakn

The assumption that they are similarly bright is questionable. First, not all of the light from the brightest stars is counted because parts of the CCD that collects the light become saturated. But more importantly, the images you see are heavily processed. Usually the interesting stuff in an astrophoto is dimmer than the brightest stars, and so the image is "stretched." The pixels on the bright end are all crowded together at similar brightnesses, and on the dim end, pixels that formerly had similar brightnesses end up with dramatically different brightnesses. Check out this link for a description of the processing that goes on even just to show you a preview image of "raw" Hubble data: http://archive.stsci.edu/hst/preview...orrection.html. Go here http://archive.stsci.edu/cgi-bin/hst...name=J8JY04060 and try viewing the image of V838 Mon using several levels of Pixel Correction (GIF Only), starting at "None." Using the None setting, you won't even see V838 Mon, one of the most fascinating objects in Hubble History.

Barakn

Yes, it does.

hipparchos

No. The Hubble's resolution is 0.05 arcsec, essentially the same as the apparent diameter of Betelgeuse.

Drakkith

Care to explain how the Hubble captured that image then?

Barakn

The picture was taken in ultraviolet light. Hubble has better resolution R in UV than visible light. A crude estimate is (using R in arcseconds = 0.21 λ/D, where λ is wavelength in microns and D is mirror diameter in meters) R = 0.21 ｘ0.122/2.4 = 0.011 arcseconds for the smallest wavelength ultraviolet light, 122 nm, visible to the Faint Object Camera that took the image. However, http://hubble.esa.int/science-e/www/...odylongid=1464 gives an even smaller value, 0.0072 arcseconds.