18                                     Lloyd Motz

appeared to be a new star in the constellation of Cassiopeia which
became as bright as Venus at its brightest and was visible even
in the day time. He made systematic observations of the po.sition
and brightness of the star which appeared in published form as
De Stella Nova and were later reproduced in his Astronomiae
Instauratae Frogymnasmata, published in i6io in Frankfurt by
Godefred Tampach. This supernova which Brahe observed is of
more than historical interest to the modern astronomer because
it is intimately related to present day research in radio astronomy.
With our radio telescopes we can detect an intense source of
radio waves in the constellation of Cassiopeia in the position of
Tycho's nova, and we must therefore conclude that novae, or
exploding stars, emit radio waves.

This conclusion is also borne out by two other supernovae that
appeared in our galaxy: the one that appeared in Taurus in the
year 1054 and is now visible as the beautiful Crab Nebula, and
the supernova in Ophiucus -which Kepler observed in the year
1604. There are no records in European manuscripts of the occur¬
rence of the 1054 outburst, but Japanese and Chinese documents
record it as having been observed on July 4 of that year. The
complete story of the Kepler supernova is contained in his
De Stella Nova in Pede Serpentarii published in 1606 by Paulus
Sessius in Prague and by Wolfgang Richter in Frankfurt. Both
the Crab Nebula and Kepler's nova are known today to be intense
radio sources.

Brahe rejected the idea that the nova he had observed was the
star of Bethlehem, presaging the return of the Saviour, and argued
that it was the coagulation of Milky Way matter into a new star,
but concluded that it would have to fade soon, as, indeed, it did,
because, he said, "anything that arises after the completion of
Creation can only be transitory."

The observations of the three supernovae so long ago in the
past have had an important bearing on present day cosmological
theories and on the theories of the evolution of stars. The occur-