Astronomy - USA (2021-12)

Double down on

DOUBLE

STARS

DOUBLE

DOUBLEDOUBLE

STARS

STARSSTARS

40 ASTRONOMY • DECEMBER 2021

Roughly half the sky’s

stars have a partner.

Here are some of the

most famous, colorful,

and compelling pairs.

BY RAYMOND SHUBINSKI

ABOVE: The Big Dipper in Ursa

Major houses a famous double

star that ancient Arabic texts

refer to as a visual test. Just at

the kink in the Dipper’s handle

is bright Mizar, with dimmer

Alcor 12' to its east-northeast

(upper left in this image).

ALAN DYER

LEFT: This meticulously hand-

drawn diagram from Edward

Crossley’s A Handbook of

Double Stars shows the orbits

of Castor A and B. RAYMOND SHUBINSKI

VIEWING DOUBLE STARS is a popular activity at star parties. The

presenter will usually point out Mizar and its dimmer companion, Alcor, in

the bend of the Big Dipper’s handle; or, in summer, telescopes are often turned

to Albireo in Cygnus, to everyone’s delight.

But double stars are often neglected by today’s serious amateur observers,

who are more interested in deep-sky objects. It’s a shame, because not only are

double stars beautiful, but they are also a challenge by which to measure the

skill of the observer and the quality of their telescope. Double stars were once

the focus of both professional and amateur observers alike, and they have

played an important role in our understanding of gravity and of the galaxy

in which we live.

Mizar and Alcor