Cassiopeiae, The Elusive Supernova Remnant
When Tycho Brahe was on his way home on November 11, 1572, his attention was attracted by a star in Cassiopeia which was shining at about the brightness of Jupiter and which had not been seen in this place before. Tycho was so impressed by this event that he devoted the rest of his professional life to astronomy only. Nevertheless, Tycho had not been the first to discover this “new” star; according to Burnham, it was probably first seen by W. Schuler on November 6, 1572. Tycho found it at about as brilliant as Jupiter, and it became soon equal to Venus. For about two weeks the star could be seen in daylight. At the end of November it began to fade and change color, from bright white over yellow and orange to faint reddish light, finally fading away from visibility in March, 1574, having been visible to the naked eye for about 16 months.
The remnant of this supernova (SN 1572) had to wait for its discovery until the 1960s, when extremely faint nebulosity was identified on Mt. Palomar photo plates near the position, and gaseous remainders were identified by their radio emission; a stellar remnant has not been found. The gas shell is now expanding at about 9000 km/s (compare with the Crab Nebula’s about 1000 only), and has reached an apparent diameter of 3.7 arc minutes. Tycho’s supernova remnant appears to be the more typical representative of these class of objects of the two.
You can find this supernova in Starry Night. An expanded image is shown at the left. Imagine the confusion of observers in the 16th century to an appearance of a “star” that could be seen even in daylight for several days. For astronomers of 16th-century Europe, the heavens were immutable. The appearance of SN1572 was a dramatic challenge to that opinion.
Today this supernova is still visible, but only with a carefully aimed telescope. The best images we have come from the Hubble Telescope.
Think of how surprised we would be, even today, if a sudden light appeared in the sky and was so bright for several days that we could see it even in daylight.
 See David Tosteson, “The Elusive Cassiopeiae,” Sky and Telescope (131, 6, June 2016, pp. 26-31)