The times. [volume] (Washington [D.C.]) 1897-1901, 1900-10-21
STARS THAT DISAPPEAR.
vnrinbfr Planets Many of which Are
EnNN tNs Dlscrye

Easy tof Observe.
1t is 204 years sisce David Fabricius
enc OF the earliest observers Of sun spots
noticed that star In the neck of Cetus
the Whale. which ne had observed in Au
gust, 1896, to be OF the third magnitude
had DISAPPEARED by October This ap.
peared an observation of great impor-
lance, since II seemed to show that the
fixed stars are not all Of them permanent
but that they might die out. Seven year:
later Bayer recorded a four magnitude
star in precisely the same position as that
which Fabricius had noted to have disap-
peared. Here, however. the matter rested
for an entire generation, and it was not
until 1898 that Eolwarda detected the star
again as of the third magnitude in Decem-
her, but found 1t disappear in the follow
ing summer to reappear again in autumn.
This star. therefore. Omicron Ceti, which
received from Helvelius the name of Mira
the wonderful star, was the first to be-
come known as periodic variable
The first star, that is to say, in historic
times There Is another more striking
even than Mira. which it seems likely
was noted by the forgotten astronomers
of Arabia or the valley of the Euphrates
centuries before even Hipparchus and
Ptolemy compiled their catalogues. This
is Beta in the constellation Perseus, de-
scribed by PtOlemy as the principal star
in tAe-head Of the Gorgon Medusa, which
the hero is represented as carrying in his
hand This star has come down to us
from the Arabs with the name AlgoI. and
Demon Star. and it is at least 4 probabili-
~ that 1t owed this name to the fact that
though ordinarily of the second magni-
tude 1t sinks down almost to the fourth at
nofI
and twenty-one hours.
The variability OF Algol was discovered
in modern times by Montanari in 1863, and
1t was rediscovered by Goodricke in 1882.
The latter observer two years later added
two other variables to the list-Beta Lyrae.
with period of very nearly thirteen days,
and Delta Cephei. with one of five and one
third days. At this date, scarcely more
than a century ago, these four stars were
almost the only variables known to us, and
variables continued to be rare objects until
the middle Of the century. Now their
numbers have been added to so greatly that
the catalogue prepared by Prof Chandler
in 1896 comprises 400. the variability of
which is fairly well established, and new
members Of the class are being discovered
every month.
The four stars first mentioned are all
we'll in view during the September nights.
The most striking star with which to be.
gin is Algol The student. avoiding all
references to Ephemerides. should look out
at regular intervals and compare the
brightness Of Algol with certain of the
neighborlng stars. Ordinarily Alpha Per.
sci will be distinctly but not very greatly
brighter than our variable. while Gamma,
Delta. Epsilon. and Zeta will be distinctly
fainter At little greater distance are
A1nbq and poto ha oh
ly brighter. the latter slightly fainter than
Algol. Alpha and Beta tranquil are at
10 great distance, and are good campari-
son stars Then Algo1 has begun to fade.
1t will not be long before the observer
will find that his star Is undergoing a
cha nge, and that it no longer nearly rivals
Alpha Persei or Gamma Andromedae in
brightness. Directly this is noticed sys-
tematic observation should be begun A
star should be chosen reasonably near,
distinctly brighter than the variable, and
a second star distinctly fainter. 1t is u.s.
ual among variable star observers to esti-
mate these differences In steps" these
steps" corresponding generally to about
A tenth of magnitude though probably the
will make his steps considerably
larger than this. The central principle,
however. is that two stars should be Sc
iSttCu. ouC vi WhiCu u tHS ODStIftE 10
cleear to be fainter than the variable, and
the other brighter and yet both OF them
pretty near the variable in brightness. The
student should further be careful to rec
ord whether the difference between the
and the fainter star is equal to
or greater or less than the difference be-
tween it and the brighter star.
Having made one Set Of satisfactory OBJ
servations. the student should leave the
star for while-say, for ha!f an hour
and then make an entirely fresh set Of
observations. II he should be fortunate
enough to hit upon the beginning of a
his second observation will show
him the star somewhat fainter than the
first. and the difference will become more
marked at a third observation. The en-
ire period of decline and recovery for
Algol is nine hours, the light fading for
four and one-half hours remaining con-
slant for few minutes. and then gradu- |
ally increasing again for another reriod
# four and one-half hours. The light
2hanges therefore at most rapid rate at |
how two and oue-four'h hours before |
or about The same interval
lIte5 ward-ihat is to say, wIen the change |
S about half completed.
The observation is a simple one. with |
10 accessories of brilliant lights or pleas |
nS COiOrS, Yet the young observer can |
not we think but experience real pleas |
ire when for the first time his observations. |
:arefully and Systematically made and duly |
show him beyond a doubt that |
lie is witnessing the dimming of the Demon |
star; that he is watching across untold |
Millions of millions of miles of space the /
partial eclipse of that far distant sun
There will be n sense OF achievement. |
greater and not less because 1t has been |
accomplished by his unaided sight than II |
lie had the help of some great instrument
And If there be in him any of the stuff Of
which astronomers are made he will turn
eagerly for other objects of study. and will
wait with much interest for other oppor-
unities Of watching AlgOl.
1t is. OF course well known now that the
ariabilty of Algol is due to its having a
ark companion which revolVes round 1t in
bout sixty-nine hours. The variation in
'cta Lyrae is of more complicated kind.
Iere there are two minima. one less pro-
ounced than the other. and We infer
therefore, that in this case both stars are
right. and that they alternately eclipse
ach other. The variation is less than with
.lgoi. being but little more than a single
Magnitude.
Delta Cephi has a variation of much the
anne amount as Beta Lyrae. but it diff
ers from that star in that it has slow
ecline and a quick recovery-,he decline
cling ninety-one hours, the recovery thr-
weight.
~ E;ss45z,l s5<yss3