Why are stars spiky? - Deep Sky Videos

Why do photos of stars often have spiky, pointy bits of them? These are called diffraction spikes and some people even add them artificially!

Here are explained by Professor Mike Merrifield (University of Nottingham) and Nik Szmanek (astrophotographer). Mike tweets at   / profmike_m  

Some image credits:
Philip Perkins: www.astrocruise.com/
Nik Szymanek: http://ccdland.net
Fred Espenak: http://astropixels.com

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