The Portland daily press., 1898-03-16
AsTAR's ECLIPSE PHOTOG RaPHED.
Scientific Feat Satisfactorily Accomplished
for the First Time at the Harvard Obser-
vatory.
(Boston Transcript.

A circular has been issued by Professor
Edward G. Pickering of the Harvard
College Observatory, regarding the re-
cent successful Photographic observation
of the occultation of twenty-six Arietis
at the observatory. The disappearance
of q bright star when occulted by the
moon is always striking phenomenon.
There is no celestial event OF which the
time is susceptible of more precise de-
termination. For many years various
plans have been suggested, both at the
Harvard Observatory and elsewhere, by
which his time could be determined with
greater accuracy than by ordinary visual
observation. In fact, the apparatus for
photographing the eclipses OF Jupiter s
satellites, used at the observatory for
several years, was devised in part for this
purpose.
On Feb. o. Edward S. King for the first
time succeeded in satisfactorily photeg-
raphing the occultation of a star. The
apparatus used was an improved form of
that constructed for photographing the
eclipse of Jupiter's satellites. The plate
was moved automatically every second
by means of an electromagnetic. A mo-
ton of about 0. 03 ON. was given to the
plate whenever the circuit WAS closed,
and OF an equal amount when 1t was
oDened Connecting the apparatus with
the standard clock, Frodsham 1927, two
images alternately faint and bright, were
obtained every second. AS The faint i'm
ages are three magnitudes fainter than
the bright images, the ratio of the dura-
tions was about one to sixteen, SO that
thu absolute durations were O. 06 and "a
seconds. 1t is here assumed that. as the
fines of exposure were very short the
chemical action was proportional to the
time This assumption is verified by
actual measurement.
Considering only the images taken DUR
ing this minute following Oh Som Os. the
bright images of 20 Arietis, as shown be
low, are equally intense including that
having an exposure lasting from Sos. 90
to 51s.00. Stree this image appears 10
bs AS bright as the others, the light OF q e
star could not kave begun to dimin1sl.
much before the time. LII the star had
disappeared suddenly at 50s.9 the Inst
image would be at least 0. IL OF 1nagnl-
tude fainter than the Others. an ainodnl
readily measurable. The next image Is
apparently invisible. Had the disappear
ance taken place at 5is.C6 the image
would appear, and would be as bright MS
the other faint images. A slight darken-
ing of the film is perceptible near the
position the next image would have had,
with an Intensity nearly equal to that OF
tho fainter images. If this were que 60
tho star it would denote that tho lsIter
suddenly disappeared at about 5is.l2: Inc
absence of the preceding image would IN
dictate more gradual disappearance. In
any case. the time is fixed at 5ls.1 to
within one-tenth Of a second. As the
clock was I'm 1884 fast, not including
armature time, the corresponding Green
w.ch Mean Time is 12h 54in EOS s. By
using shorter exposures, the uncertainty
in the time of disappearance can doubt
less be greatly reduced, especially in the
case OF the brighter STARS. Since salts
factory images Of a6 Arietis, magnitude,
6.l, were obtained IN CSC, it is proba bic
that occulta ions OF stars as faint as the
ninth magnitude can be observed photo
graphically.
In connection with this work, it is in.
erestinR to note that tho determination
photographically of the POSITION Of the
moon, by means of = star to be occulted
was one OF the subjects Investigated by
Professor G ?. Bond forty years ago. He
obtained number Of photographs Of the
moon and Virgins shortly before the
occultatinu ct the latter on June 2, 1851.