Astronomy - USA (2021-12)

WWW.ASTRONOMY.COM 43

about four times the mass of our Sun; it

shines with intensely blue-white light.

Astronomers long wondered whether

these two stars were physically related.

In the last few years, the European Space

Agency’s Gaia spacecraft has provided

data suggesting this is an optical double,

also known as a line-of-sight double.

Regardless, the close visual effect is

spectacular and Albireo is

always a favorite object for

viewing.

But perhaps aiming

to take Albireo’s spot is

Izar (Epsilon [ε]

Boötis), also known as

Pulcherrima, Latin for

“the most beautiful.”

That name was

bestowed by Friedrich

Georg Wilhelm von Struve,

who split the star into two col-

orful companions using the Great

Dorpat Refractor in Estonia. He said the

primary was gold and the secondary an

appealing blue. Other observers claim

the stars look yellow and green, respec-

tively. Epsilon can be difficult to separate

with a small telescope but is well worth

the effort.

Yet another crown jewel of the sky,

Gamma Delphini is located in the con-

stellation Delphinus’ Job’s Coffin aster-

ism. An easy double to split, observers

describe it as having unusual colors.

SEEING CLEARLY

Throughout the 19th century and well

into the 20th, both professional and

amateur astronomers preferred

refracting telescopes. Refractors offer a

clear aperture free of the distortion and

diffraction caused by the secondary

mirror in reflecting telescopes. But two

drawbacks of early refractors were their

long focal length and their chromatic

aberration, which cause poor images

and color distortion, respectively. The

development of achromatic and

apochromatic lens systems has

eliminated these issues. I currently

observe double stars with both a 6-inch

Celestron refractor and an 8-inch

Celestron NexStar Evolution HD reflector.

Both scopes provide excellent images, as

will many others. Even a good pair of

binoculars can provide enjoyable

viewing of wide double stars. — R.S.

Nineteenth-century observer Admiral

William Henry Smyth called it a “beau-

tiful double star” and said the two stars

appear yellow and light emerald. Others

have said they’re orange and lime. What

do you see?

One of the most glorious stars in the

sky is Antares, the heart of the Scorpion.

The name means “rival of Mars.” And

anyone who has scanned the summer

sky knows that Antares has a distinct

red hue. At a distance of 550 light-years,

this star is a nearby red supergiant.

In 1844, Scottish astronomer James

W. Grant observed a companion star

near Antares. The secondary star was

seen again in 1846 by American astrono-

mer Ormsby M. Mitchel. The two stars

are separated by 2.5" and their

colors have been described

as fiery red and green

or blue. The prolific

English astronomer

the Rev. Thomas

W. Webb said that

the companion

appeared “yellow,

with flashes of deep

crimson alternating

with a less proportion of fine green.”

Antares is so bright that the fainter star

can be overwhelmed by its glare, making

this delightful double star a challenge to

split, depending on the telescope and sky

conditions.

Also in Scorpius, Acrab (Beta Scorpii)

at the root of the Scorpion’s

uppermost claw is yet another

colored double star. With a sepa-

ration of more than 13", this system

resolves into two stars at relatively

low power. Beta appears truly white,

while the second star has been called

lilac or green. The discrepancy may be

due to contrast between the two stars.

Like Porrima, Acrab lies on the ecliptic

and is occasionally occulted by the

Moon.

Our final destination is the left foot

of the Princess Andromeda, which holds

the delightful double star Almach

(Ga mma A ndromedae). First

split in the late 18th cen-

tury, the two stars

have been described

as orange and

emerald green

(like Gamma

Delphini).

Others have

seen gold and

indigo blue. This

contrasting pair provides yet another

challenge for color perception.

See for yourself

Observing double stars is a rewarding

experience. They give us the opportunity

to challenge our equipment, our sky con-

ditions, and, most of all, our own observ-

ing skills. If you have the patience to

watch stars like 61 Cygni over the course

of many years, you’ll see that the sky isn’t

static, but dynamic and alive. And ulti-

mately, the challenge of visually observ-

ing double stars gives a sense of connec-

tion with the cosmos that no photograph

can possibly convey.

This highly magnified shot shows Antares’

much smaller close companion, Antares B.

GIUSEPPE DONATIELLO

Antares

This sketch of Beta Scorpii, made with an

8-inch f/5.9 Newtonian telescope, shows the

white primary accompanied by a secondary

that appeared blue to the observer. JEREMY PEREZ

Beta Scorpii (Acrab)

Almach, located in the foot of Andromeda, has

a small companion that may appear either

green or blue, depending on your color

perception. NVN271/WIKIMEDIA COMMONS

Gamma Andromedae

(Almach)

Raymond Shubinski has observed all of

these double stars and more. He also enjoys

comparing his observations with those of

bygone astronomers.