The times., 1901-06-02
THE TWINKLING OF STARS
DR.. See Explains What Appears to
BE Vibrations of Planets.
Air Currents Affect observations
With Either the Naked Eye or
With the TeIescope-ResuIt Of He
cent Scientific study of Air waves.

cent Scientific study of Air Waves.
1t has been often asserted that those
stars which twinkle are suns. and that the
twinkling process, being visible to the
naked eye. is sufficient proof that the
twinkling star is a sun, like the sun seen
by people on the earth.
Or. T. ]. ]. See, member OF the as.ro-
nomical stan Of the Naval Observatory.
while not denying that twinkiing stars are
suns, asserts that the twinkllng Is due to
air currents which are in motion some.
where between the observer and the star.
Did you ever notice. ne asked, the
vibrating air just around the hot stove
pipe, or over the top of a chimney? II
you have, you will doubtless have observ-
ed also that the edge of the stovepipe
and chimney seemed to be moving also.
That is what the astronomer notices when
ne looks through the telescope at the
stars. The planets are so near that they
can be seen as disks with welI-defined
borders or circumference. But stars
which are much farther of do not appear
as disks. but as shining, vibrating, and
oscillating points of light If there is a
current Of air of considerable force NOV
ing between the observer and the star
there will be so much motion or twink
ling as to make it impossible to see the
outline of the star itself. Sometimes cross
currents will intervene and add to the
disturbance and render a good obserya-
tion wholly impossible. For exar1ple. sun
pose the wind is blowing in one direction
some miles above the earths surface and
further down current of air, or wind.
is blowing Ia direction which either
crosses the direction OF the upper current
at right angles or obliquely, these osefIIa-
. n " 81
telescope and make the star look as if il
were vibrating with great velocity. This
Is especially apparent over a hot dry ter
rltory such as the Arizona Desert Here
the lower heated air is in intense vibra-
ton and is in strong contrast to that
Whlch lies over a high mountain in a
cooler atmosphere. Consequently. obser-
vations made from a high altitude. such
as from the top of mountain. Will per-
nit of keener and sharper observation
Recent studies of the air waves visible
IN telescopes have led me to connect these
aerial agitations with the scintiIIations. of
the hxed stars. These undulations have
not been considered by previous investi-
gators, and it seems probable that they
constitute the true cause of stellar scin-
ullation. which has heretofore been some
what obscure. In the case of the naked
is gathered is about two millimetres in
diameter, and hence any intercepting
wave which might turn the light of the
star to one side by this amount would
cause the star to twinkle suddenly; or if
it did not wholly disappear, the wave
would at least disperse the light into
spectrum and the eye would recognize a
change in brightness and a rapid sue
cession of spectral colors. The action of a
wave is essentially similar to that of a
lens, for it must always distort the lunni-
nous wave-front. But it would seldom
happen that the eye would be in the To-
Gus of the wave. and hence, while there
would be ineessant fuctuatiOn in bright
ness as the waves pass before the eye.
there would also be a rapid succession OF
colors.
IF. in the small area, covering the pu-
pill the rays from different waves, or diff
ferent parts OF the same wave, should
interfere, as must occasionally happen.
there would be total momentary extinc-
tion of the star. When the interference
did not amount to extinction there would
be a sudden diminution and then an in
crease in brightness. with play of sue
eessive colors. If the waves happened to
be conspicuous, the scintillations would
be correspondingly marked
when the waves are conspicuous and
violent, the scintillation is marked. both
to the naked eye and in the smaller tele-
scopes. When the waves are small there
is no proper seinullation in the larger
telescopes, though parts Of the image will
undergo considerable motion and disper-
sion of color, yet scintillation continues
in the telescopes of small apertures, and
is always noticeable with the naked eye
when the length of the wave surpass-
es the aperture of the telescope there is
always some scintillation, while If the
waves are shorter, only partial selntilla-
ton or none at all can be perceived
THE intensity of the scintillatfon is
function of the altitude of the star above
the horizon. This may be explained by
the fact that low down the numerous
successive waves superposed in the iine
of vision frequently act as combined
waves and thus increase the visible ef-
fects upon the stars brightness, position,
and color.