Evening star., 1932-03-11
NEW LINE IN SUNS
CORONA REVEALED
|. BYECL|PSEPHOTOS
Discoveries by Navy's Ex-
petition to Tin-Can Is
land Are Announced.
COMPLETE SPECTRUM
GOTTEN FIRST TIME
Characteristic Lines of Mysterious
Substance Known as Coronium
Are Found.
BY THOMAS r. HENRY.

New clues concerning the nature of
the suns corona. which blossoms like
gigantic dahlia" during some total
eclipses, were uncovered by observa
tions taken during the Navy's eclipse
expedition to Tin-Can Island, in the
Southern Pacific, last Summer.
Prof. S. A. Mitchell of the University
Of Virginia, who was in charge of the
spectroscopic work on this expedition,
has just reported on the results of
laboratory analysis of his photographs.
For the first time he secured a COM
plete spectrum of the corona, contain
ing the characteristic lines of the
mysterious substance known as coro-
mum which. so far as is known, occurs
nowhere else In nature.
New Line Shown.
He found the spectrum lines of the
corona covered a wave-length range of
approximately 900 angstrom units and
his photographs show at least one new
line which is not duplicated by any
known substance. The nature of coro-
mum, the hypothetical substance known
only from its spectrum, remains a
mystery. Prof Mitchell points out. 1t
long was believed to be an unknown
element possibly prevalent in minute
quantities through nature, but most
abundant in the extremely tenuous,
luminous disk of gas circling the
eclipsed sun like halo The rare gas
helium was first identified in the sun
through its spectrum lines and after
ward found on the earth.
But numerous investigations have
failed to reveal anything correspond
ing to coronium and during the last
few months all of the hitherto hypo-
thetical elements needed to fill gaps
in the atomic table presumably have
been discovered. No place is left for
"coronium" as distinct element. The
report mentions the suggestion that it
may be neutral oxygen
The characteristic corcnium spectrum
line comes in the wave length range
associated with green. The new line
found In the corona by Prof. Mitchell
was in the red wave length range and
does not check with anything now
known. 1t is believed. however, to-
represent rare state of some known
substance.
The coronium, Prof Mitchell found.
Is mostly in the inner corona which
extends to within about 600 900 kilo-
meters of the surface of the sun.
Results Summarized.
Prof. Mitchell, in his report pub
ltShed in the Astrophysical Journal
summarizes the results of corona OBJ
servations on several eclipse observa-
t1ons; These show, he says, that there
are two main types of corona. One
is the minimum type, with extended
streams near the suns equator and the
other Is the gigantic dahlia" type.
circular in outline, with the blackened
disk OF the sun in the center. The
shape OF the corona, he points out, evi-
dentiy depends upon conditions within
the sun and hence is only a temporary
phenomenon which can have no con-
slant shape.
The giant dahlia" corona. he saws.
apparently comes two years before the
period OF the suns maximum activity
as revealed by sun spots and solar
promlnenceS The minimum corona
comes two years before the minimum
point in the solar activity Thus there
IS an indirect relationship between
changing coronal shapes and sizes and
the ll-year sunspot cycle. The regular
changes in the shape Of the corona.
Frol. Mitchell points out, have escaped
notice because the phenomenon can
De observed only for very brief period
at the time of total eclipse. When all
the periods of observation for many
years past are put together they amount
only 10 a short time