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Message: <blockquote data-quote="Binastro" data-source="post: 3633504" data-attributes="member: 111403">Hi Maljunulo, post 36.A difference of 0.1 magnitude is 10% (9.65%).There are different magnitudes. Visual, photographic and others.The comparison stars and main star have to be the same colour, otherwise errors occur.With say Betelgeuse or Mars it is difficult to judge because of the warm colour.Also the comparison stars need to be at the same elevation to avoid atmospheric extinction. In a good sky compensation can be made.The comparison stars must be non variable. But different catalogues may give different values.There are many things to consider to get it right.The main binocular star may  be 2/5ths brighter than A and 3/5ths fainter than B. The resulting magnitude might be mag 7.63, which is rounded to mag 7.6.One must be careful to centre the stars or have them equidistant around the centre field.Telescopes are used for faint stars, down to mag 15 visually and considerably fainter with cameras.I haven't made estimates for a while, but could estimate to mag 0.1 values. Many people cannot make star estimates.Comet and extended objects are more difficult, but are given to 0.1 mag, but probably only accurate to mag 0.2 maybe worse. There are different methods and one must state the method used.Several observers use ancient Japanese 10x50 Porros. They have made 100,000 or many more estimates over decades.This is all a bit different than saying how bright the white columns are in binoculars 120m away from me in the daytime or twilight.P.S.Visual estimates are still commonly made.Photometry can be more accurate, say to 0.01 magnitude, but only if one sets up the equipment to an exact standard.Photometry can also give a light curve with very short time intervals or for extended periods.</blockquote>

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