Tycho’s star has achieved a romantic reputation by being fancifully identified with the “Star of Bethlehem,” said to have led the wondering Magi from their eastern deserts to the cradle-manger of the Savior in Palestine. Many attempts have been made to connect this traditional “star” with some known phenomenon of the heavens, and none seems more idle than this. Yet it persistently survives, and no astronomer is free from eager questions about it addressed by people whose imagination has been excited by the legend. It is only necessary to say that the supposition of a connection between the phenomenon of the Magi and Tycho’s star is without any scientific foundation. It was originally based on an unwarranted assumption that the star of Tycho was a variable of long period, appearing once every three hundred and fifteen years, or thereabout. If that were true there would have been an apparition somewhere near the traditional date of the birth of Christ, a date which is itself uncertain. But even the data on which the assumption was based are inconsistent with the theory. Certain monkish records speak of something wonderful appearing in the sky in the years 1264 and 945, and these were taken to have been outbursts of Tycho’s star. Investigation shows that the records more probably refer to comets, but even if the objects seen were temporary stars, their dates do not suit the hypothesis; from 945 to 1264 there is a gap of 319 years, and from 1264 to 1572 one of only 308 years; moreover 337 years have now (1909) elapsed since Tycho saw the last glimmer of his star. Upon a variability so irregular and uncertain as that, even if we felt sure that it existed, no conclusion could be found concerning an apparition occurring 2000 years ago. In the year 1600 (the year in which Giordano Bruno was burned at the stake for teaching that there is more than one physical world), a temporary star of the third magnitude broke out in the constellation Cygnus, and curiously enough, considering the rarity of such phenomena, only four years later another surprisingly brilliant one appeared in the constellation Ophiuchus. This is often called “Kepler’s star,” because the great German astronomer devoted to it the same attention that Tycho had given to the earlier phenomenon. It, too, like Tycho’s, was at first the brightest object in the stellar heavens, although it seems never to have quite equaled its famous predecessor in splendor. It disappeared after a year, also turning of a red color as it became more faint. We shall see the significance of this as we go on. Some of Kepler’s contemporaries suggested that the outburst of this star was due to a meeting of atoms in space, and idea bearing a striking resemblance to the modern theory of “astronomical collisions.”