Why do bright stars appear pointy on photos?
Like in this photo.
Posted May 23, 2011, 2:50 PM UTC
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That's a nice photo, BTW.
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/r/spaceporn for other good stuff, if you're not already a subscriber.
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Thanks for sharing! Have an upvote!
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[deleted]
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Nobody has given you an explanation about why you are wrong yet. What you are describing is also caused by diffraction, but is responsible for the stars not appearing as points, but rather as having apparent extent. A wider aperture reduces the effect, and increases resolution (up to the limits allowed by atmospheric conditions, and even that can be pushed with adaptive optics).
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This wiki page answers:
http://en.wikipedia.org/wiki/Diffraction_spike
Thats a pretty good explanation. To clarify, you do not see diffraction spikes in refractor telescopes ( ones that uses lenses instead of mirrors or mirror+lens combinations)
The "arms" that hold the secondary mirror on the front of a reflector telescope block small amounts of light from reaching the primary mirror itself. See this image for a decent example: http://scienceinthesky.files.wordpress.com/2010/09/telescopespider.jpg?w=250&h=198
What about sun stars through camera lenses? http://www.flickr.com/photos/kuzeytac/4009342936/
It seems to be related to the number of blades in the aperature, but any additional explanation would be nice.
I'm not a camera/optics guy so I could only speculate that it may, in fact have something to do with the shutter.
Usually modern consumer dslrs use focal plane shutters. I quite understand how they could produce effects like sun stars. Ill check it out further. Thanks for your ideas.
Apparently it's Fraunhofer diffraction by the aperture. source
Thanks.
how come I see them with just my eyes on street lights at night?
I believe that's the light bouncing off your eye lashes.