The very brilliant new star which shone forth suddenly in the
constellation of Cassiopeia in the year 1572, was made the object
of special studies by Tycho, who proved that the star had no
sensible parallax and consequently was far beyond the planetary
regions. The appearance of a new star was a phenomenon not
unknown to the ancients, since Pliny records that Hipparchus was
led by such an appearance to make his catalogue of the fixed
stars. But the phenomenon is sufficiently uncommon to attract
unusual attention. A similar phenomenon occurred in the year
1604, when the new star--in this case appearing in the
constellation of Serpentarius--was explained by Kepler as
probably proceeding from a vast combustion. This explanation--in
which Kepler is said to have followed. Tycho--is fully in accord
with the most recent theories on the subject, as we shall see in
due course. It is surprising to hear Tycho credited with so
startling a theory, but, on the other hand, such an explanation
is precisely what should be expected from the other astronomer
named. For Johann Kepler, or, as he was originally named, Johann
von Kappel, was one of the most speculative astronomers of any
age. He was forever theorizing, but such was the peculiar quality
of his mind that his theories never satisfied him for long unless
he could put them to the test of observation. Thanks to this
happy combination of qualities, Kepler became the discoverer of
three famous laws of planetary motion which lie at the very
foundation of modern astronomy, and which were to be largely
instrumental in guiding Newton to his still greater
generalization. These laws of planetary motion were vastly
important as corroborating the Copernican theory of the universe,
though their position in this regard was not immediately
recognized by contemporary thinkers. Let us examine with some