THE NOVAE, OR NEW STARS
New stars, or temporary stars, we have already mentioned in connection
with variables. They are, next to comets, the most dramatic objects in
the heavens. They may be variable stars which, in a brief period,
increase enormously in brightness, and then slowly wane and disappear
entirely, or remain of a very faint stellar magnitude.
In the ancient historical records are found accounts of several such
stars. For instance, in the Chinese annals there is an allusion to such
a stellar outburst in the constellation of Scorpio, B. C. 134. This was
observed also by Hipparchus and, no doubt, it was the immediate
incentive which led to his construction of the first known catalogue of
stars, so that similar happenings might be detected in the future. In
November, 1572, Tycho Brahe observed the most famous of all new stars,
which blazed out in the constellation Cassiopeia. In something over a
year it had completely disappeared.
In 1604-1605 a new star of equal brightness was seen in Ophiuchus by
Kepler; it also faded out to invisibility in 1606. Kepler and Tycho
printed very complete records of these remarkable objects. The
eighteenth century passed without any new stars being seen or recorded.
There was one of the fifth magnitude in 1848, and another of the
seventh magnitude in 1860; and in May, 1866, a star of the second
magnitude suddenly made its appearance in Corona Borealis; and one of
the third magnitude in Cygnus in November, 1876. The latter was fully
observed by Schmidt of Athens and became a faint telescopic star within
a few weeks. It is now of the fifteenth magnitude.
In 1885 astronomers were surprised to find suddenly a new star of the
sixth magnitude very close to the brightest part of the great nebula in
Andromeda; it ran its course in about six months, fading with many
fluctuations in brightness, and no star is now visible in its position
even with the telescope. Stars of this class are known to astronomers as
Novae, usually with the genitive of the constellation name, as Nova
Andromedae.
In 1891-1892 Nova Aurigae made its spectacular appearance and yielded a
distinctly double and complex spectrum for more than a month. Many pairs
of lines indicated a community of origin as to substance, and accurate
measurement showed a large displacement with a relative velocity of more
than 500 miles per second. For each bright hydrogen line displaced
toward the red there was a dark companion line or band about equally
displaced toward the violet much as if the weird light of Nova Aurigae
originated in a solid globe moving swiftly away from us and plunging
into an irregular nebulous mass as swiftly approaching us. Parallax
observations of Nova Aurigae made it immensely remote, perhaps within the
Galaxy, and it still exists as a faint nebulous star.
In February, 1901, in the constellation Perseus appeared the most
brilliant nova of recent years. It was first discovered by Dr. Anderson,
an amateur of Glasgow, and at maximum on February 23 it outshone
Capella. There were many unusual fluctuations in its waning brightness.
Its spectrum closely resembled that of Nova Aurigae, with calcium,
helium, and hydrogen lines. In August, 1901, an enveloping nebula was
discovered, and a month later certain wisps of this nebulosity appeared
to have moved bodily, at a speed seventy-fold greater than ever
previously observed in the stellar universe.
According to Sir Norman Lockyer's meteoritic hypothesis, a vast nebulous
region was invaded, not by one but by many meteor swarms, under
conditions such that the effects of collision varied greatly in
intensity. The most violent of these collisions gave birth to Nova
Persei itself, and the least violent occurred subsequently in other
parts of the disturbed nebula, perhaps immeasurably removed. This
explanation would avoid the necessity of supposing actual motion of
matter through space at velocities heretofore unobserved and
inconceivably high. A recent photograph of Nova Persei, by Ritchey,
reveals a nebulous ring of regular structure surrounding the star. The
great power of the 60-inch has made it possible to photograph even the
spectra of many of the novae of years ago which are now very faint. After
the lapse of years the characteristic lines of the nebular spectrum
generally vanish, as if the star had passed out of the nebula--a plunge
into which is generally thought to be the cause of the great and sudden
outburst of light.
Many novae have recently been found in the spiral nebulae, especially in
the great nebula of Andromeda.