Scientific theories may be accepted on the basis of a weighing of many complex factors rather than a single determinative observation or crucial experiment. From antiquity, Copernicanism had been rejected due to a failure to observe stellar parallax. Eventually Copernicanism became accepted on other grounds, despite the absence of stellar parallax. Stellar parallax was not confirmed until 1827, when Wilhelm Bessel found a shift in the position of double star 61 Cygni.