Evening star. [volume] (Washington, D.C.) 1854-1972, 1898-07-02
A COMET NOW DUE.
CELESTIAL Visitor May Drop in Upon
Us at Any Minute.
he

Clestfal Visitor May Drop in Upon
Us ut Any Minute.
From the Philadelphia Record
Encke's comet is on the Astronomical al pro-
gram for this month-that g, according to
| calculation, it will this month make its
perlhelion passage" round the sun-and for
some weeks observers havs been on the
watch for 1t. Under ordinary circumstances
we might expect to receive the first report
of its Sighting from the Lick observa-
t6ry as has latterly been the case with the
greater number of the periodic comets.
whose positions when in their approach to
the sun they become near enough to be
seen can be determined with a far degree
OF accuracy. Owing, however, to its south
ern position, Encke's comet this year is not
SO favorably placed as it was at its last
return, in 1894, and very likely the first
sight of 1t will be obtained in the southern
hemisphere, and not until it has already
passed its perihelion.
The comet which bears the name of
Encke is the longest known of the periodic
comets, and has the shortest period of them
ALL and 1t is for other reasons also an OBJ
ject Of especial interest. Its first recorded
appearance was in 1876, over century ago.
1t was then discovered at the Paris obser-
vatory, in the constellation Aquarus. A
few years later it was rediscovered, this
time in Pegasus, by Miss Caroline Hers
chel, and it was for third time caught
up by astronomers in 1918. On this last
occasion it, or its elements" fell into the
master hands of Encke, who, after having
vainly attempted to compute for it para
boiic course finally determined by then
newly invented method of calculation that
its orbit was an ellipse and, moreover, an
ellipse SO remarkably small that the comet
would complete the circuit Of it in about
three and a third years.
EBcke fixed upon the month and the day
W hen it should return in 1922. The comet
kept its appointment with the astronomer
within a few hours, but, being on that oc-
casion unfaVoraoly situated, 1t was seen
only in the southern hemisphere and by but
enc observer Since then it has been reg
ularly on the program of astronomers, and
has been seen at every return.
The frequent visits of Encke's comet have
permitted of it being observed and studied
more thoroughly than any other of this
mysterious class of celestial bodies. 1t is a
cul ious fact, probably due to the unstable
character of the forces which hold its parts
together-and in a measure also to the Cir
cumstance that 1t is sometimes more IA
forably situated for observing than at other
times-that it never presents twice the
same appearance on it's successive returns.
Usually it is a tailess, telescope affair
mere bunch of celestial thistle-doWn, with
star-like spot in the center-but occa-
sionally it throws out a short tail and be-
comes visible to the naked eye.
But more perplexing to astronomers than
it's Protean shape is the fact that its period
is shortening. 1t seems to set at defiance
the usual rules of motion that hold among
the celestial bodies, and without any as
signable cause it has habit of arriving at
perihelion couple of hours before the time
set for its arrival there by the mathemati-
cal astronomers Its orbit is slowly but
surely growing smaller. In fact, 1t is fall
ing into the sun, and none of the astrono-
mers can say why.
1t has been suggested, however, as a pos
sble explanation of this behavior of the
comet that it is retarded in it's movement
by some resisting medium too subtle to
affect appreciably the movements of the
massive planets, yet sufficiently dense to
produce the effect observed in the case of
body so ethereal as comet. In default of
any other known medium the mysterious
"ether" which physicists now hold to per-
wade all space-the medium whose vibration
gives rise to the phenomena of light and
electricity and, possibly, Of gravitation-has
been charged with this interference with
the comets movement Another theory
which of late has met with more favor is
that the retarding medium consists of the
countless millions of minute meteors which
are known to lie within the limits of the
solar system and thought to be espe-
cially numerous in the neighborhood of the
sun. But a serious obstacle in the way
of both of these theories is that none of the
other short-period comets is affected in the
same way. This exceptional conduct OF
Encke's, comet is a puzzle which astrono-
mers have yet to solve.