Evening star. [volume] (Washington, D.C.) 1854-1972, 1890-05-17
FAMILIES OF STARS.
Stellar Clusters and Nebul8-An Inter.
esting Lecture by Prof. Searle.

estlng Lecture Dy frOf. Searle.
Prof. George M Searle lectured yesterday
| afternoon at the Catholic University on 'sMui-
tiple Stars, Clusters and Nebula." Among
other things he said:
All over the heavens we find what are
called double stars; stars, that is to say, SO
close together that in some cases they fail to
be recognized as double, except with a tele-
scope of considerable power Often, however,
| they are more easily separable, and they were
known even during the last century to exist in
considerable numbers. They were supposed
to present this appearance merely by accident
one of the stars being far behind the other
| and falling accidentally in line with it. 1t was
| not till Sir William Herschel had made sur
vey OF the whole heavens, with the idea mainly
OF using the double stars, on this supposition,
for the determination of parallaxes that the
idea came to mems minds that, after ALL per-
haps there really was physical connection be-
tween them, and that instead of being at
| widely different distances, they were really at
the same distance from the earth.
Sir VIM. Herschel. the great founder, we may
| say of solar physics, was the first to put this
idea on a scientific basis He construc ted in
| 1852 catalogue of 227 double stars in addition
to the AZ previously known, and by 1855 he had
found 434 more. In 1903 he was able to bring
positive proof of their physical connection by
stars had mutual revolution round each other
as If under the influence of mutual gravity.
He went so far as to assign periods to some of
them. For Castor he found a period Of 342
years In 1924 time gave the final seal to this
conclusion of Herschei and the orbitai move
ment had become them in many cases, quite
unquestionable. In one case, for instance, one
revolution had been fully accomplished and
another one begun.
ORBITS OF DOUBLE STARS.
No method OF computing accurately the or
bits of double stars was discovered till 1880,
which is rather strange, considering that the
problem is quite simple. This may be ex-
planned by the want of thorough belief and
keen interest in the matter previous to the OBJ
servations of Sir John Herschel and Sir James
South iii 1874, just spoken OF. These double
stars as stated in a previous lecture, are the
means by which We arrive at some idea of the
stellar masses. Given their distances from US
we know how far they are from each other, and
from that ana their time of revolution we find
how great their mass Is by the amount of curv-
| allure of their orbit. We cannot, however, tell
| in this way the separate masses of the stars I'M
less we can lind out not merely the relative but
the absolute movement Of one Of them. In
| some cases, however, this has been done. The
bright star Sirius found by observations of
Its actual. place to move in little orbit in the
sky. No companion however, was seen until
| 1862, when Mr.. Clark, with the new Chicago
| telescope, discovered the companion which had
previously been indicated. The star PrOcyon
| shows similar movements, but no companion
| to 1t has yet been found We are, however,
quite certain that 1t exists
CONTRAST OF coLoRs
curious fact about double stars is tho con-
trast in color which often occurs in them when
their brilliancy is notably different. In this
case the color of the fainter star is ALWAYS
nearer to the blue end of the spectrum.
| In many cases We find more than two stars
in system. The orbit, however, of a triple or
a multiple star is always beyond the power of
man to calculate. The problem of three
| bodies. so called, except under certain circum-
stances, such as exist III the solar system, has
never BEEN and we may safely say never will
| be, solved.
There are combinations OF stars, however.
much more complicated than these They are
| called clusters. The most conspicuous ex-
! ample of these is the well-known group Of the
| Pleiades. 1t is not however, so rich and full
| as most of those which the telescope reveals
Another one visible to the naked eye is that
| known as Praesepe, or the Beehive, in the
| constellation Cancer.
| The question naturally rises, are these stars
crowded together in this way really suns like
| our own and the others which have been ex-
| amined? 1t was some years ago generally
taken for granted that they were, and that
! these wonderful aggregatlons were separate
universes, like the one composed of all the
separate ones which We see with the naked eve
ana the telescope. but TINS view Is hardly en-
tertained ut the present time. 1t is far more
probable that they are within the limits of our
| own stellar system. Whether the stars are of
ordinary size or not cannot be said with GER
tainty. but it seems probable that they are
comparatively small.
| CLUSTERS AND NEBULE.
| There seems to be a connection between
| these clusters and what are known as nebule
Nebule are patches Of light appearing like
parts OF a comets tail, or in some cases like a
! telescope comet itself. They were formerly
| supposed to be clusters like those we have seen
only beyond our available object power and
| that is all But it has been lately demon
strated by the spectroscope that this cannot be
the case in many instances because this instu-
ment shows clearly that many of the nebule
are gaseous. Nebule also variable in some
cases in their brilliancy, and it seems probable
| that some which have actually existed have
| disappeared. In some cases they evidently
connected with stars, as in the nebule found
I in the Pleiades. The whole number of nebule
| which have been discovered is about 10000
The size Of some of them is astonishing For
instance able to say with confidence
that the section of the great nebua of Orion,
| which We see, is Mt least ten thousand times as
| large as that of our whole planetary system 1t
| is generally believed that nebule are the raw
material out Of which suns and planetary sys-
TENS have been made, though we probably
shall never be entirely certain regarding that
point III this world.