Sky & Telescope - December 2018 - 11

SOLAR ECLIPSE

ECLIPSE PHOTO: MILOSL AV DRUCK M ÜLLER / PE TER A NIOL /
SH A DIA H A BBA L; ECLIPSE SIM UL ATION: PREDICTIV E SCIENCE;
BE TA PICTORIS B: ESO / A-M. L AG R A NG E E T A L.

Scientists Successfully Predict Shape of Solar Corona
SCIENTISTS ATTEMPTED TO predict the shape of the Sun's corona as
it would appear during the total solar
eclipse on August 21, 2017. Observations conﬁrmed that they got the broad
strokes right.
The corona, an intricate crown of
thin, super-hot plasma around the Sun,
expresses our star's hidden magnetic
angst. Its charged particles respond
to the magnetic ﬁeld by twisting into
loops, bands, and even erupting into
interplanetary space. Solar physicists
led by Zoran Mikiü (Predictive Science)
report August 27th in Nature Astronomy
that they can accurately predict the
appearance of the corona one week in
advance - an important milestone on

the path to predicting the oncoming
solar wind.
The team offered a new model of
the Sun's outer layers that takes into
account how their heat and magnetic
ﬁelds stimulate the corona. Using observations of the Sun taken on July 16 and
August 11, 2017, as a baseline, Mikiü
and colleagues ran a simulation on a
NASA supercomputer to calculate the
solar corona's appearance 10 days later.
They then compared these visualizations to images taken by ground-based
photographers during totality.
Encouragingly, the simulated corona
has the same general shape as its reallife counterpart, with a few bold, bright
plasma "streamers" ﬂowing out into

parcos and Gaia missions to measure
the star's wobbles on the sky, due to the
planet's gravitational tugs on its host.
Unlike previous estimates, the new
result doesn't depend on assumptions
about the star or disk. The astronomers pinned Beta Pictoris b's mass to
between 9 and 13 times that of Jupiter.
Snellen and Brown used the same measurements to conclude that the planet
takes at least 22 years to circle its star.
While there are many observations
of disks that have yet to form planets
and thousands of known planetary

u The planet Beta Pictoris b (arrowed) is visible
orbiting its host star in this composite image
from the European Southern Observatory's 3.6m telescope and the NACO instrument on the
ESO's 8.2-m Very Large Telescope.

p An enhanced photograph of totality (left)
compares well to the simulated view (right).

space, as well as intervening loops similar to those seen dancing in the images.
The simulated Sun doesn't perfectly
mimic the corona's ﬁner features, but
its large-scale correspondence gives
solar astronomers conﬁdence that
they're on the right track to understanding the physics of the Sun's outer
layers. It also enables them to test their
ideas of solar physics. With improved
measurements of solar magnetic
ﬁelds, such as those expected from
NASA's Parker Solar Probe (S&T: Nov.
2018, p. 9), models like this one could
soon track the Sun's evolution and
potentially improve space weather forecasts, the authors conclude.
■ EMILY SANDFORD

systems, the number of known, stillforming planets is small. As one of the
youngest directly imaged planets, Beta
Pictoris b provides a vital data point in
understanding how young gas giants
accumulate material. Moreover, Gaia
data may help astronomers investigate
many more planets in the same way.
■ JOHN BOCHANSKI

sk yandtelescope.com * DECE MBE R 2 018

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Sky & Telescope - December 2018

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