Sky & Telescope - April 2021 - 13
N IG E L S H A R P ( N S F ) / F TS / N SO / K PN O / AU R A / N S F
X The Sun emits
every wavelength
of visible light, but
elements in the solar
atmosphere absorb
specific wavelengths,
imprinting the spectrum with dark bands.
While these absorption lines provide
insight into the Sun's
chemical composition, understanding
the interior is a far
more difficult task.
looks like a colorful barcode, and in effect that's what
it is. Scanning the solar spectrum tells us the Sun is
at least 98% hydrogen and helium; metals make up
the remaining 2%.
An alternative method for taking a solar inventory focuses on the way the Sun hums. Huge flows
of material swell and sink under the solar surface,
meaning the underbelly of our star is in a constant
state of flux. These motions create sound waves that
bounce around inside the Sun, with some making
it to the photosphere, resulting in an undulating
surface that throbs in and out. Just as seismologists
on Earth track the passage of earthquakes through
the planet to learn more about its internal structure,
helioseismologists can use the Sun's pulsations to
uncover its composition and structure. The vibrations are sensitive to both the Sun's temperature and
its composition.
" The higher the abundance of metals, the more
opaque solar material is, " says Sarbani Basu (Yale
University). Opacity is a measure of how " seethrough " the layers of the Sun are, and it affects the
speed and pattern of the sound waves reaching the
solar surface. Metals in particular absorb energy and
impede the waves' path to the surface.
For years these two independent yardsticks for
the Sun's makeup were largely in harmonious agreement. Then, in the 2000s, spectroscopists dropped a
bombshell: The Sun had far fewer metals than they
had originally said. The two sides have been duking it
out ever since.
sk yandtelescope.org * APRIL 2 021
13
http://www.skyandtelescope.org
Sky & Telescope - April 2021
Table of Contents for the Digital Edition of Sky & Telescope - April 2021
Contents
Sky & Telescope - April 2021 - Cover1
Sky & Telescope - April 2021 - Cover2
Sky & Telescope - April 2021 - 1
Sky & Telescope - April 2021 - Contents
Sky & Telescope - April 2021 - 3
Sky & Telescope - April 2021 - 4
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Sky & Telescope - April 2021 - Cover3
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