Evening star. [volume] (Washington, D.C.) 1854-1972, 1909-09-16
LOOKING FOR HALLEY'S COMET
PHOTOGRAPHIC SEARCH AT
NAVAL OBSERVATORY.
Pictured at Heidelberg, Approaching
Earth's Orbit at Million
Miles Day.

| Photographic search for Halleys comet,
which is now approaching the orbit of the
earth at the rate of a million miles day,
is the subject of renewed interest at the
United States naval observatory, mas
much as it has been announced that the
celestial visitor has been photographed
by the Heidelberg observatory.
Photographing comet long before 1t
can be observed through a great tele-
| scope Is perhaps the climax of the as
Economical progress of the age. In fact.
celestial photography has reached a de-
gree Of success within the last fifteen
| or twenty years In revealing the wonders
of the heavens far beyond the most ro-
| mantle imagination of the early pioneers
| in this art.
| To Prof. Barnard belongs the honor Of
| having made the first Photographic dis
covery of a comet, In 1892, since which
| time the camera has revealed much of
the wonderful structure of the comets
tails and the rapid and remarkable
changes they so frequently undergo.
Careful positions of a comet are first
computed in order to find the part Of
the sky where it is supposed to be, and
also to determine the daily motion as ac-
curately as possible. Though the sup
posed location of the comet in the sky
| may be in error as much as a degree or
| more the apparent motion of the comet,
! assuming the known motion of the earth
and the comet, could not be much in
error from night to night. otherwise it
| would soon run off from its ephemeris.
1n order to take a long exposure on the
| region the daily motion of the comet is
| wanted. This implies that every ten min
utes the comet would be on new part
Of the plate. and If it made no impression
in the first ten minutes it would make
none at all, no matter how long the plate
was exposed. Thus, to increase the eff
fective exposure on the comet the daily
| motion is computed, and that motion
given. so as to keep the comet stationary
on the plate,
Exposure Two and a Half Hours.
The exposures vary from two to two
and one-half hours for each sitting, and
If plate contained the object a careful
search would make its Identification sure
on a single night. Photographic plates
used in hunting comets and planetoids
cover the region we'll over an area at
least of two degrees on all sides of the
objects predicted position
The Photographic film is far more SEN
sitive than the human eye, cannot become
fatigued and permanently registers all it
sees, and thus very faint objects, like
Halley's comet. far away in the depths
of space, can be seen five or six months
| in advance of the eye of an observer
through great rejecting telescope
For astronomical discoveries beyond
! the limit of telescope vision, such as
comets. nebulae and minor planets, the
world is indebted to a number of tireless
workers in this branch of astronomy
| such as Rutherford, Draper, Higgins
and, later, E. E. Barnard and Max Wolf
| who is the first to photograph Halley's
| comet.
| A Photographic chart of the heavens
! was hardly dreamed of a quarter of a
century ago, while today the old method
| of charting the stars is almost obsolete