Evening star., 1938-12-28

OF making comparative measure
ments of longitude and thus tying
the map of the world together in
a co-ordinated whole.
Two explanations now are con-
sidered most plausible. One is that
a radio impulse is speeded. up in
the direction of the earth's rotation.
The other Is that the crust of the
earth actually is stretched out by
tidal forces of the sun and moon.
Some calculations indicate that the
differences in apparent longitude
depend upon the position of these
bodies.
The moving airplane experiment,
DR.. Stetson said, probably can be
relied upon to prove or disprove
| the other hypothesis. 1t has been
impossible up to the present be-
cause there has not been sufficiently
delicate time receiving apparatus.
Moon and Venus Remeasured.
New measurements of the mass
of the moon and. of the planet Venus
were announced to the association
today by astronomers of the Naval
Observatory. Both, according to
Drs. H. R. Morgan and F. P. Scott
OF the Observatory staff, are a trifle
heavier than hitherto has been sup
posed. when compared with the
masses of the sun and earth.
The two astronomers calculated
what they refer to as "dynamical
masses determined by the pull
they exert and the consequent dis
turbance they produce in the orbits
of other heavenly bodies. This, they
explained, hardly can be expressed
in tons, which are purely earthly
standards of measurement.
Venus used to be considered as
being 100000 as heavy as the sun.
She now appears to be /407 900
a difference of a good many mil
lions of tons if the planet could be
placed on earthly scales and
weighed.
This is all tied up, they explained,
with the length of the day. or the
period of the earth's rotation, now
approximately 80 seconds ahead of
schedule.
Evidence for tides Of light on stars
was presented to astronomers today
by DR.. William A. Luby of the Uni
versity of Kansas City.
Probably the most useful objects
IN the heavens are class of stars
known as cepheid variables, one of
which is the North Star. At in
tervals varying from IL hours to SO
days they increase suddenly in
brightness from 20 to 400 per cent.
It has been found that the fire.
quency of these changes depends
strictly on the ordinary brightness
of the star.
Consequently whenever a cepheid
is found 1t is possible to measure
quite accurately the distance to that
part of the heavens by comparing
its actual brightness to its apparent
brightness and calculating the dis
tance light must travel to cause 50
great a loss.
The reason for these fluctuations
IN brightness, however, has not been
satisfactorily explained. It all can
be satisfactorily explained, DR.. Luby
said, on the assumption that every
cepheid Is a double star-one men,
Der of the pair being very large
and bright and the other small and
dark, about one-tenth the mass Of
the sun. If the small star came
close enough to the big one, he ex.
planned, it would raise a tide almost
a million miles high and the volume
of the tidal wave would be severa
hundred times the volume of the
sun.
Disturbance Dies Slowly.
"Cepheids," he said, ARE double
stars. The volume of Delta Cephei
the first one of these known, has 6
diameter 26 times that of the sur
and a volume 1900 times the vol.
ume of the sun. When the tida
wave passes over the visible hemi
sphere of the star the light rises
On the farther hemisphere of thu
star the wave may be partially Wis.
ible or wholly eclipsed. Maximum
light comes when the wave Is neal
the center of the visible hemisphere
OF the star and minimum light wher
1t Is on the farther hemisphere. Tn,
tidal wave is so enormous that tn,
disturbance caused by its passins
dies down slowly.
THE material composing the wav,
does not move around the star, bu
merely moves up and down alonl
the radius. Hence when the wavl
crest is near the center of the Wis
ible hemisphere the velocity of ap
proach is greatest and when it i
near the center of the invisible
hemisphere the velocity of recession
If it is visible and observable, i
greatest"
This fits perfectly, DR.. Luby said
the observed changes in this typ
Of stars which have excited tn
wonder Of astronomers-especiall.
the fact that when the light /
brightest its source appeared to b
approaching the earth with a tire
mendous velocity.
The great cities Of the Atlanti
Coast Of the United States stand o.
1DDn n AAuuH AualA