The Washington times., 1901-10-13

One of the most important and inter
esting departments of astronomy-a!
well as one of the least known popular
ly-is the measurement and recording
of the comparative magnitude of the
stars-a task which has been carried
on, doubtless, since the very beginning
of astronomical science. In this reck
oning of magnitude, which is known a.
photometry-the measurement that is
of starlight-it is interesting to note
that an American astronomical estab-
lishment stands among the first, if not
as the very first, in the world, photome-
try having been for years one of the
principal subjects taken up by the Har-
ward Observatory. both in Cambridge
and at Arequipa, Peru, and the results
of the work which it has accomplishei
having been accepted as standard all
over the world.
The first star catalogue, giving 1,OSO
stars. was published by Hipparchus in
the year 125 B. c. 1t has come down
to us through Ptolemy Of Alexandria,
who nearly 300 years later, in 140 A. D.,
produced his "Megale SyntaXis''-the
'Almagest,' of the Arabian and Moor
ish astronomers-which, either directly
or through the corrected catalogue that
was based on 1t by the Persian astrono-
mer, Abd-al-rahman al-Suh, was the
worlds standard until Ulugh Bleigh
brought out a new catalogue at Sa-
maracand about 1450 A. D. The famous
catalogue of Tycho Brahe-the last of
the mediaeyal, or the first of the mod
ern, astronomers-in 1880, was the last
important catalogue produced without
the aid of the telescope.
Hipparchus and Ptolemy arranged
the stars in six classes, the first class
comprising the brightest-about 20 in
all-while the sixth class contained
those which could just be made out by
the naked eye. After the telescope
came into general use magnitudes were
extended downward as fainter stars
were brought into view by the in
creasing power of the instruments EN-
ployed. For many years each astrono-
mer used his own scale. Herschel at the
Cape of Good Hope especially using
very high numbers-a tendency that
has been so reduced since his time that
his 10th magnitude is very nearly the
14th on the scale now generally employ
ed. This scale more closely corresponds
with that of Argelander, the great Ger
man author of the "Durchmusterung,
or catalogue of the stars in the North
ern heavens, which enumerates over
S24, 600 stars: the largest number yet
catalogued.
llnh 1rVafT do g hae &c
typical stars To which the others may
be conveniently referred. The stars
which do not exactly correspond in
magnitude with a typical star are ex-
pressed in fractional terms of the near
est magnitudes, decimals being usually
employed, although Ptolemy and even
Arselander used thirds. Employing
the decimal system, a star of "a mag |
nitude will be shade brighter than a !
star of 5.5 and so on. An exception is |
that certain stars, such as Arcturus |
and Sirius, and the planet Jupiter when |
at his brightest, are more than a mag
nitude brighter than stars of the first |
magnitude. Aldebaran, for example, |
and are therefore expressed in mega
tive magnitudes, that is to say, they
are preceded by the minus sign. Jupi-
ter, for instance, approaches almost the
second negative magnitude-minus ?
or is l6 times brighter than a star Of
the first magnitude.
1t is significant Of the great accom-
plishment Of American astronomy that
there was no universally accepted sys-
TEN OF photometry until the publica-
tion Of what is now known as the Har-
ward photometry-the H p" as II is
called by astronomers. This
was contained in Volume XIV of the
Annals Of the Harvard Observatory,
under the title Of Observations with
the Meridian Photometer during the
Years lS59-lsSz'-a massive volume Civ
ing a list Of 1920 stars in the Northern
sky visible TO the naked eye in the
latitude Of Cambridge, and intended 10
include all stars not fainter than the
sixth magnitude between the North
Pole and 80 degrees south Of the celes-
tial equator. To this original list an
other. Volume XIV of the Annals,
has since been added. Technically such
a piece of work is called a Uranome-
tria, or catalogue of ''naked-eye stars"
The similar work produced by Prof.
Pritchard at oxford, for example, con-
tanning the magnitudes of 2,7S4 stars
thus observed. was entitled ''Uranome
tria Nova Oxoniensis." The Harvard
was SO elaborate and SO
accurately done that it has been prac-
tically accepted everywhere, and the
magnitude Of all new stars given on
the Harvard scale. A striking illustra-
ton of the use TO which it is now put
last spring when the new
star appeared in the constellation Per
;eus. Among the observers who gave
their results on the Harvard scale were
Ni1land and Gyllenskold Of Sweden,
Pereira Of the Portuguese observatory
n the Azores, the staffs of the British
Association and the AS
economical Society of France, and the
3fficers of the Radcliffe Observatory at
oxford, as wen as practically all Am
srican astronomers.
As would be supposed, it takes a
trained eye TO notice the finer differ
.nces in star magnitudes. On the mod
,rn scale a first magnitude star would
be expressed as ranging from 050 to
80. a second magnitude star from 1.5O ,
70 $50, and so on. For instance, Cas-
.or which was measured as L56 in the
II. p" would be called of the second
magnitude, while its twin star, PoIlux,
he brighter of the Gemini, is a first
magnitude star, measured as liz The