The New Heavens | Page 9

separately, the fringes behave
differently. As the slits are moved apart a point is reached where the
fringes completely disappear, only to reappear as the separation is
continued. This effect is obtained when the slits are at right angles to
the line joining the two stars of the pair, found by this method to be
0.0418 of a second of arc apart (on December 30, 1919). Subsequent
measures, of far greater precision than those obtainable by other
methods in the case of easily separated double stars, show the rapid
orbital motion of the components of the system. This device will be
applied to other close binaries, hitherto beyond the reach of
measurement.
[Illustration: Fig. 18. Ring Nebula in Lyra, photographed with the
60-inch (Ritchey) and 100-inch (Duncan) telescopes.
Showing the increased scale of the images given by the larger
instrument.]
Without entering into further details of the tests, it is evident that the
new telescope will afford boundless possibilities for the study of the
stellar universe.[*] The structure and extent of the galactic system, and
the motions of the stars comprising it; the distribution, distances, and
dimensions of the spiral nebulæ, their motions, rotation, and mode of
development; the origin of the stars and the successive stages in their

life history: these are some of the great questions which the new
telescope must help to answer. In such an embarrassment of riches the
chief difficulty is to withstand the temptation toward scattering of effort,
and to form an observing programme directed toward the solution of
crucial problems rather than the accumulation of vast stores of
miscellaneous data. This programme will be supplemented by an
extensive study of the sun, the only star near enough the earth to be
examined in detail, and by a series of laboratory investigations
involving the experimental imitation of solar and stellar conditions,
thus aiding in the interpretation of celestial phenomena.
[Footnote *: It is not adapted for work on the sun, as the mirrors would
be distorted by its heat. Three other telescopes, especially designed for
solar observations, are in use on Mount Wilson.]
CHAPTER II
GIANT STARS
Our ancestral sun, as pictured by Laplace, originally extended in a state
of luminous vapor beyond the boundaries of the solar system. Rotating
upon its axis, it slowly contracted through loss of heat by radiation,
leaving behind it portions of its mass, which condensed to form the
planets. Still gaseous, though now denser than water, it continues to
pour out the heat on which our existence depends, as it shrinks
imperceptibly toward its ultimate condition of a cold and darkened
globe.
Laplace's hypothesis has been subjected in recent years to much
criticism, and there is good reason to doubt whether his description of
the mode of evolution of our solar system is correct in every particular.
All critics agree, however, that the sun was once enormously larger
than it now is, and that the planets originally formed part of its
distended mass.
Even in its present diminished state, the sun is huge beyond easy
conception. Our own earth, though so minute a fragment of the
primeval sun, is nevertheless so large that some parts of its surface have

not yet been explored. Seen beside the sun, by an observer on one of
the planets, the earth would appear as an insignificant speck, which
could be swallowed with ease by the whirling vortex of a sun-spot. If
the sun were hollow, with the earth at its centre, the moon, though
240,000 miles from us, would have room and to spare in which to
describe its orbit, for the sun is 865,000 miles in diameter, so that its
volume is more than a million times that of the earth.
[Illustration: Fig. 19. Gaseous prominence at the sun's limb, 140,000
miles high (Ellerman).
Photographed with the spectroheliograph, using the light emitted by
glowing calcium vapor. The comparative size of the earth is indicated
by the white circle.]
But what of the stars, proved by the spectroscope to be self-luminous,
intensely hot, and formed of the same chemical elements that constitute
the sun and the earth? Are they comparable in size with the sun? Do
they occur in all stages of development, from infancy to old age? And
if such stages can be detected, do they afford indications of the gradual
diminution in volume which Laplace imagined the sun to experience?
[Illustration: Fig. 20. The sun, 865,000 miles in diameter, from a direct
photograph showing many sun-spots (Whitney)
The small black disk in the centre represents the comparative size of
the earth, while the circle surrounding it corresponds in diameter to the
orbit of the moon.]
STAR IMAGES
Prior to the application of the powerful new engine of research
described in this article we have had no means of measuring the
diameters of