The times. [volume] (Washington [D.C.]) 1897-1901, 1901-01-13

Inc astronomers at the Naval OpSei va
tory have just completed a task which
will enable science to make new and
much more accurate measurement of the
scale upon which the whole universe is
constructed. This is the establishing the
position in the heavens of the planet
Ercs. on which depends an accurate
knowledge of the distance between the
sun and the earth. This distance is now
given only approximately as $685. 600,
miles. which. however. is not precise
within a limit of $4,000 miles.
The estimate of the distance of any
star. or of the size of the orbits of any
pair of double stars: in fact. all measure
ments in the celestial spaces depend upon
a knowledge of the distance OF the earth
from the sun. To determine this, di
rect trigonometrical method, such as is
used in surveying and such as may be ap-
piled to the distance of the moon from
the earth, cannot be used. as no instru-
ments can be constructed of the neeessa-
ry delicacy. The only means by which
the result was possible OF attainment was
by the determination of the exact dis
lance between the earth and any of the
other planets in our solar system, and
this being now accomplished in the case
OF Eros, the distance between the sun
and earth VIII soon be made known with
practical exactness.
Eros, the planet TO which astronomy is
indebted for important results, was dis
covered in 1889 by Herr G. Witt, of the
University of Urania. II is enc of the
large group of planetOids, which is con-
stantly being enlarged by new obserya-
lions. Copernicus had proved, and KEEP
Ter and others had drawn attention to,
the greatness of the gap between the or
bits of Mars and Jupiter. Then, in 1871,
| Sir William Herschel detected the planet
| Uranus at distance from the tun agree
| ing with the next term of a series which
| Titus and Bode had noticed as almost
| exactly representing the distances of the
! other planets, except that for one term,
| between those which coTrespcnded with
| Mars and Jupiter, there was no planet
| known.
While twenty-four astronomers were
planning a search for this missing mem
| Der of the solar system Plazzi fwho was
not among those who had thus especially
| set themselves to the task detected at
! Palermo on the LIST of January, 1901,
! little planet afterward names Ceres. Three
| more were found by two out of the TWEEN
| ty-four astronomers in the course of the
| next six years. a fifth was found in
i 1S45, after interval of thirty-eight
years; then they commenced TO be re-
vealed in considerable numbers, owing to
| improved instruments, and especially to
| photography In 1858 the total had
reached 1OO and now it is nearly $50. AZ
| ter the detection of a few of the brighter
| ones the search for others became a
wearisome process. New star charts had
to be constructed with great labor so as
to include these fainter stars.
If small star was noticed through the
! telescope which could not be found on any
chart, it was watched carefully and, if it
| exhibited an ofbital movement, 1t was en-
tered on the list Of planetoids, and the
| various elements OF its orbits were calcu-
lated and recorded. But just as this kind
of work began to grow very laborious in
deed TO observers. photography came as a
welcome aid 1t did away with a. need
for star charts, and of any c1mpaI 10, Of
observations with them. A photograph
plate happened, by accident, to be left too
long exposed, and during that time a
little planet had taken occasion to record
the fact of It's existence by means Of q
small orbital line traced among the dots
representing the surrounding stars. Since
the early part of 1892 out OF 100 discoy-
cries of such planets, only three or four
have been made by the old method Of eye
observation.
The existence of these planetoids has
been accounted for by the hypothesis that
they constitute the wreck OF an extinct
planet which, by some natural convulsion.
has exploded in space. 1t is the nearnt IS
to the earth Of Eros which has enabled
, such valuable results 10 accrue hpm lis
: discovery. In size It is extremely 81 !,
! being only twenty miles in diameter,
; which renders it possible TO obsdrVe only
at such times as 1t approaches near 10 the
earth. sri then only by means of pow
orful equatorial telescope. Its average
distance from the sun is less than that Of
Mars and again, It comes within proX-
unity to our planet not much exceeding
one-third of the nearest distance within
which Mars ever approaches II. With the
, exception of the moon, therefore, 1t is. by
far. our nearest neighbor in space. Its
orbit Is G most surprising and novel one,
resembling in its elIipse. that Of a comet
Up to the appearance of Eros on the
scene, the path OF Mars had formed prac-
ticaliy the boundary beyond which minor
planets had scarcely transgressed The
: new planetoid came A., 100000 miles within
the mean distance of Mars.
Astronomers have sought, by measuring
the distance between other members OF
our planetary group and the earth, to at
| tain the results now achieved by the sue
cessful computation OF the distance 10
| Eros but such attempts have invariably
| proved failures Venus was once selected
for the purpose and observations were
made OF that planet on those rare occa-
sions when It passes in transit across the
suns disc. But the glare of the sun s
| light, ill-defned edge of the suns cssc
and the atmosphere OF Venus itself, COM
biued to deprive such observations OF the
! necessary accuracy.
Apart from some other methods, in
volving long periods of time and highly
complicated theoretical Investigations in
their use, attention was next given to an
attempt to obtain the distance of the
planet Mars when 1t makes It's nearest
APPROACH to the earth. II was, however,
found to be difficult to measure the exact
position of the centre of its disc, where
upon It was suggested that one OF the
pIanetoids be selected for the purpose.
The new planet, Eros, proved of the Ut
most value for such observations, because
the accuracy of the result of these de
ponds upon the nearness TO the earth OF
, the planet that IS observed. The method
Of calculation employed depends upon the
ratio of the planets distance to the linear
distance between two observations made
at intervals of time as far apart as posi-
BILE Thus two observations were made
Of Eros, when visible, every twenty-fouI
| hours one soon after sunset and the Other
| shortly before sunrise. The difference II
, the directions in which the planet is seer
from two such standpoints. as compared
: with the positions OF the stars around II
which are so distant that no change IL
produced in their apparent places, Is large
enough to be capable of very accurate
measurements, this distance being larger
and more easily determined the nearoI
the body observed is to the earth. The
movements Of the earth and the planet
in their orbits In the interval can be al