Sky & Telescope - December 2019 - 61

"What lies before us is an illimitable
field, the existence of which was
scarcely suspected ten years ago . . ."

CA MILLE FL A M M A RION: PUBLIC DO M AIN; TITLE PAG E L'ASTR ONOMIE:
L'ASTR ONOMIE (1882) / PUBLIC DO M AIN

ogy and astrophysics were still in their infancy, and of little
"practical" interest to most astronomers. Moreover, powerful new tools like spectroscopy and photography were just
beginning to hit the scene. Of the 333 pages in Newcomb's
Astronomy for Everybody, nearly 200 were devoted to the solar
system, while some 40 covered such basics as time, longitude,
the celestial sphere, and the seasons. An additional 40 or so
pages fell under the heading "The Fixed Stars." Just six pages
dealt with cosmology. Similarly, of Todd's A New Astronomy's
480 pages, only the last 50 (excluding the index) covered
subjects beyond navigation and the solar system in a chapter
titled "The Stars and the Cosmogony."
In an 1887 speech that was reprinted in the January and
February 1888 issues of The Sidereal Messenger, Newcomb
confessed that so far as astronomy was concerned, "we do
appear to be fast reaching the limits of our knowledge." Yet by
1902, when he addressed the Astronomical and Astrophysical
Society of America, he made clear that his views had changed.
"What lies before us is an illimitable field," he averred, "the
existence of which was scarcely suspected ten years ago. . . ."
Perhaps astronomical knowledge was not so bounded after all!

What Fuels the Sun?
What was known about the physics of our Sun at the opening of the 20th century? Not a lot, it would seem. Beyond
its overall dimensions and evident surface features, virtually
nothing was known of our star's real age and inner workings.
Flammarion, Todd, and Newcomb all dealt expansively with
visible solar phenomena, especially sunspot frequency, size,
and shape, in their public writings. For instance, issue No. 4
in 1894 of L'Astronomie featured many beautiful lithographs
of major sunspots, as well as a paper on the physical properties of the Sun that detailed its rotational aspects and what
sunspots might tell us about the solar interior. Since features
like prominences and the corona were only visible during
relatively rare total eclipses, not much was known of them,
and based on early spectroscopic data, Newcomb described
them as ". . . large masses of incandescent vapour burst forth
from every part of the Sun."
The fundamentals of nuclear fusion wouldn't become
clear until the 1920s and 1930s when Arthur Eddington
suggested, and later Hans Bethe and others showed, that the
Sun's main source of energy involved the fusion of hydrogen
to helium. Prior to that, vague theories of meteoric impacts,
solar contraction, and heat output were proposed, which, if
true, would make the Sun at most a few million years old,
something most scientists knew couldn't be the case. As Todd
noted, "Only one possible explanation remains; if the Sun is
contracting upon himself [sic], no matter how slowly, gases
composing his volume must generate heat in this process. The
eminent German physicist, von Helmholtz first proposed this
theory of maintenance about 1850, and it is now universally
accepted." Agreeing that the Sun's heat was maintained by
uniform contraction, Todd speculated that the Sun, then
thought to be about 20 million years old, would've shrunk to
half its present diameter in 5 million years and "might continue to emit heat sufficient to maintain certain types of life
on our earth" for an additional 5 million years. He figured
the solar system life expectancy at 30 to 40 million years.
tt AT THE EYEPIECE
Camille Flammarion perches
before the 240-mm (9½-inch)
Bardou refractor at his observatory in Juvisy-sur-Orge, c.
1885.
t FIRST RELEASE The
first issue of L'Astronomie,
the cover page for which
is shown here, came out in
January 1883 (though it was
written in 1882). The popular
magazine was printed monthly
through 1894, after which
time it merged with the Bulletin mensuel de la Société
Astronomique de France, the
official journal of the French
Astronomical Society.
sk yandtele scope.com * D EC E M B E R 2 019

61


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Sky & Telescope - December 2019

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