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Page 62
[Illustration: Fig. 81.--Constellation Lyra, showing place of the
Ring Nebula.]
Mira, or the Wonderful, in the Whale (Fig. 68), is easily found when
visible. Align from Capella to the Pleiades, and as much farther,
and four stars will be seen, situated thus:
*
* * *
The right-hand one is Mira. For half a month it shines as a star
of the second magnitude. Then for three months it fades away, and
lost to sight; going down even to the eleventh magnitude. But after
five months its resurrection morning mes; and in three months
more--eleven months in all--our Wonderful is in its full glory
in the heavens. It its period and brilliancy are also variable.
The star Megrez, d in the Great Bear, has been growing dim [Page
222] for a century. In 1836 Betelguese was exceedingly variable, and
continued so till 1840, when the changes became much less
conspicuous. Algol (Fig. 68) has been already referred to. This
slowly winking eye is of the second magnitude during 2d. 14h. Then
it dozes off toward sleep for 4h. 24m., when it is nearly invisible.
It wakes up during the same time; so that its period from maximum
brilliancy to the same state again is 2d. 20h. 48m. Its recognizable
changes are within five or six hours. As I write, March 25th, 1879,
Algol gives its minimum light at 9h. 36m. P.M. It passes fifteen
minima in 43d. 13m. There will therefore be another minimum May 7th,
at 9h. 49m. Its future periods are easy to estimate. Perhaps it has
some dark body revolving about it at frightful speed, in a period of
less than three days. The period of its variability is growing
shorter at an increasing rate. If its variability is caused by a
dark body revolving about it, the orbit of that body is contracting,
and the huge satellite will soon, as celestial periods are reckoned,
commence to graze the surface of the sun itself, rebound again and
again, and at length plunge itself into the central fire. Such an
event would evolve heat enough to make Algol flame up into a star of
the first magnitude, and perhaps out-blaze Sirius or Capella in our
winter sky.
None of the causes for these changes we have been able to conjecture
seem very satisfactory. The stars may have opaque planets revolving
about them, shutting off their light; they may rotate, and have
unequally illuminated sides; they may revolve in very elliptical
orbits, so as to greatly alter their distance from us; they may
be so situated in regard to zones of meteorites as [Page 223] to
call down periodically vast showers; but none or all of these
suppositions apply to all cases, if they do to any.
_Temporary, New, and Lost Stars._
Besides regular movements to right and left, up and down, to and
from us--changes in the intensity of illumination by changes of
distance--besides variations occurring at regular and ascertainable
intervals, there are stars called _temporary_, shining awhile and
then disappearing; _new_, coming to a definite brightness, and so
remaining; and _lost_, those whose first appearance was not observed,
but which have utterly disappeared.
In November, 1572, a new star blazed out in Cassiopeia. Its place
is shown in Fig. 67, ch g being the stars
d *
g ch
in the seat of the chair, and d being the first one in the back.
This star was visible at noonday, and was brighter than any other
star in the heavens. In January, 1573, it was less bright than
Jupiter; in April it was below the second magnitude, and the last
of May it utterly disappeared. It was as variable in color as in
brilliancy. During its first two months, the period of greatest
brightness, it was dazzling white, then became yellow, and finally
as red as Mars or Aldebaran, and so expired.
A bright star was seen very near to the place of the _Pilgrim_,
as the star of 1572 was called, in A.D. 945 and 1264. A star of
the tenth magnitude is now seen brightening slowly almost exactly
in the same place. It is possible that this is a variable star
of a period of about three hundred and ten years, and will blaze
out again about 1885.
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