IntensityHydrogen absorption spectrumWavelength (nm)400 500 600 70068 ASTRONOMY • JUNE 2019A: The solar wind is composed
of a plasma of positively and
negatively charged particles
(protons and electrons) with
temperatures up to 2.7 million
degrees Fahrenheit (1.5 million
degrees Celsius). Such high
temperatures mean that these
particles are moving so fast that
they can escape the gravita-
tional attraction of the Sun and
are ejected from the Sun’s outer
layer, the corona, at speeds
between 150 and 500 miles
(250 and 800 kilometers) per
second. The winds trace the
solar magnetic field as it forms
a complex structure of closed
loops, with some field lines
staying close to the Sun and
others extending far past Earth.
Since these charged par-
ticles were first hypothesized
in 1918 by Sydney Chapman,
a multitude of studies andhundreds of spacecraft have
focused on learning more
about their physical properties.
One of the most famous space-
craft is the Solar and
Heliospheric Observatory
(SOHO), launched in
December 1995 and still in use
today. One of SOHO’s instru-
ments can detect the number
of charged particles of different
energies hitting its sensor.
Particles with smaller energies
(1–2 keV; 1,000 to 2,000 elec-
tron volts) come from the solar
wind, while large energies
(>10 MeV; 10 million electron
volts) come from large solar
eruptions. By determining the
number of these particles hit-
ting the sensor over a fixed
period of time and knowing
the mass of these protons and
electrons, it is possible to
extrapolate the mass of theAstronomy’s experts from around the globe answer your cosmic questions.
SOLAR STORMS
particles being ejected from
the Sun during a solar storm.
Kathryn Neugent
Ph.D. Candidate and Research
Associate, Department of Astronomy,
University of Washington,
and Lowell Observatory,
Flagstaff, ArizonaQ: HOW DO SCIENTISTS
DETERMINE THE CHEMICAL
COMPOSITIONS OF THE
PLANETS AND STARS?
Cristina Montes
Muntinlupa, PhilippinesA: The most common method
astronomers use to determine
the composition of stars, plan-
ets, and other objects is spec-
troscopy. Today, this process
uses instruments with a grat-
ing that spreads out the light
from an object by wavelength.
This spread-out light is called a
spectrum. Every element —
and combination of elements
— has a unique fingerprint
that astronomers can look for
in the spectrum of a given
object. Identifying those fin-
gerprints allows researchers to
determine what it is made of.
That fingerprint oftenappears as the absorption of
light. Every atom has electrons,
and these electrons like to stay
in their lowest-energy configu-
ration. But when photons car-
rying energy hit an electron,
they can boost it to higher
energy levels. This is absorp-
tion, and each element’s elec-
trons absorb light at specific
wavelengths (i.e., energies)
related to the difference
between energy levels in that
atom. But the electrons want to
return to their original levels,
so they don’t hold onto the
energy for long. When they
emit the energy, they release
photons with exactly the same
wavelengths of light that were
absorbed in the first place. An
electron can release this light
in any direction, so most of the
light is emitted in directions
away from our line of sight.
Therefore, a dark line appears
in the spectrum at that particu-
lar wavelength.
Because the wavelengths at
which absorption lines occur
are unique for each element,
astronomers can measure the
position of the lines to deter-
mine which elements are pres-
ent in a target. The amount ofASKASTR0
Q: WHENEVER I READ ARTICLES ABOUT
SOLAR STORMS, THEY TALK ABOUT
BILLIONS OF TONS OF CHARGED
PARTICLES THAT ARE EJECTED. HOW
ARE THESE AMOUNTS CALCULATED?
Ralph Heide, El Segundo, CaliforniaEach element absorbs light at specific wavelengths unique to that atom.
When astronomers look at an object’s spectrum, they can determine its
composition based on these wavelengths. ASTRONOMY: RICK JOHNSONThe astronauts of Apollo 12 — Alan Bean, Pete Conrad, and Dick Gordon
— experienced a solar eclipse while returning home from the Moon.
Their spacecraft flew through Earth’s shadow, allowing them to capture
this image on their 16mm motion picture camera. NASA/JSC