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.''

In 1670, 1848, and 1860 temporary stars made their appearance, but
none of them was of great brilliance. In 1866 one of the second
magnitude broke forth in the ``Northern Crown'' and awoke much
interest, because by that time the spectroscope had begun to be