STELLAR FAÇADES by Christopher Crockett

24 NOVEMBER 2019 • SKY & TELESCOPE

Astronomers are linking arrays of

telescopes together to reveal the

long-hidden visages of faraway suns.

Seeing

Stars

F

or all the time that humanity has spent gazing at the

stars, we still know shockingly little about what they

actually look like. Even with the biggest telescopes,

nearly every star except our Sun appears as a speck of light,

their surfaces hidden from view.

Some stars, however, are ready for their close-up.

At the southern tip of the constellation Andromeda sits

Zeta Andromedae, a moderately bright orange giant that is

now part of an elite club: It is one of a handful of stars to

have its surface mapped by astrono-

mers. In 2016, Rachael Roettenbacher

(Yale University) and colleagues

revealed the star’s portrait in new

detail: a patchy orb 15 times as wide as

the Sun and slathered in gargantuan

dark spots.

Zeta’s portrait isn’t like the gor-

geous space images that grace maga-

zine covers. This picture is blurry

and pixelated. But to astronomers it is captivating, and a

reminder that much about stars remains a mystery.

In the case of Zeta, the puzzle is its pockmarked face. Star

spots mark where magnetic fi elds punch through the surface,

and Zeta’s spots are laid out differently than spots on the

Sun. While sunspots gather in mid-latitude bands, symmetri-

cally straddling the equator, Zeta’s show up everywhere with

no discernible pattern. The Sun is free of spots at its highest

latitudes; Zeta has one large spot squatting on its north pole.

“Every star is uniquely complicated,” Roettenbacher says.

“We don’t have too many of these surfaces, but we do see

that they’re all distinctly different.”

“People don’t realize that stars are not that well known,”

says Fabien Baron (Georgia State University). But a hand-

ful of observatories are beginning to change all that. These

facilities combine many telescopes to see details no single

telescope can see and fi nally reveal the faces of the stars.

The Trouble with Stars

“Everything we do in astronomy is based on our understand-

ing of stars,” says Michelle Creech-Eakman (New Mexico

Institute of Mining and Technology). Stars light up the dark-

ness and churn out the raw ingredients needed to build more

stars, planets, and people. “If we don’t get the stellar physics

right, we can’t answer questions that are important for galax-

ies.” Our knowledge of other planetary systems, she adds,

also depends on assumptions about their host suns.

A star’s surface is its primary connection with the uni-

verse. It’s the gateway through which matter and energy pass, BA

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