The definition of a professional astronomer is one who gets paid to do it. But the difference between that and an amateur, who technically does it for fun, is getting hard to tell. Take this image of Pluto and its moon Charon taken by so-called amateur astronomers Antonello Medugno and Daniele Gasparri from Italy:
The bright blob on the right is Pluto, and Charon is on the left. The separation is 0.7 arcseconds, an incredible feat (the Moon is 2500 times wider than this in the sky). This is definitely Charon; it's at the correct position, separation, and brightness. They nailed it. Mind you, Charon wasn't even discovered until 1978 by a pro, using a 61 inch telescope! The image above was using a 14" telescope, and is in fact much better than the discovery image. In 30 years of progress, a much smaller commercial telescope can do better than a professional setup could. Wow. Also, an amateur used an iPhone (and a telescope) to capture this image of Jupiter:
Sure, it's not the best, but c'mon, it was taken with an iPhone. We live in the future. Still no flying cars, but we live in the future.
Edited to add: I did not include any of the technical descriptions of the Charon image, and I should have.
Equipment: Meade L200GPS 14" at f/25, with a Starlight Xpress SXV-H9 CCD Image scale: 0.15"/pixel, unbinned Exposure: 6 seconds/frame Filters: R +Ir (Baader) Final image: 21 frames, median combined, deconvolved to enhance sharpness At the time, Pluto was 31 AU away, at a mag of 13.9 and Charon was mag 15.5. The images were taken on August 19, 2008.