Sky and Telescope - June 2018 - 54
JUNE 2018 OBSERVING
Deep-Sky Wonders by Sue French
t If you find yourself under dark skies, try to
spot Nu1 and Nu2 Coronae Borealis without
optical aid. At magnitude 5.4 and 5.6 respectively, they're bright and far enough apart that
you may be able to make the split with your
ship, the stars aren't physically related.
Although they might be roughly the
same distance away from us, somewhere in the vicinity of 600 light-years,
they're moving in very different direc2
tions on the sky.
Just 1.6° west of Nu1, Sigma (σ)
CrB is a colorful but closer duo you can
admire in a small scope. My 130-mm
refractor at 37× shows an unevenly
bright pair of close but cleanly split
stars that both gleam yellow, the companion ﬂoating 7.4″ west-southwest of
its primary. They lie 70 light-years away.
Next door in the Herdsman's
arm, we can procure a delightDetermining the colors of double stars - sometimes
ful two-for-one. Kappa (κ) and Iota (ι)
brilliant, sometimes subtle - can be tricky even for
Boötis are only 36′ apart, making their
couplets accessible in the same ﬁeld of
view. The 130-mm at 23× shows Kappa
as a close, yellow-white pair, with the
4.5-magnitude primary guarding a
6.6-magnitude companion to its westInstead of being white, they often shine
each pair more personally our own.
southwest. Kappa is a visual binary,
with a colored light, offering in their
Let's visit some of this season's shining
whose measure in 2016 placed the
strange couples admirable associations of
jewels and see what colors you detect.
stars 13.1″ apart. Southeast of Kappa,
contrast, where the astonished eye sees
We'll begin in the Northern Crown
Iota's stars vaunt greater color contrast,
wed emerald ﬁres with those of ruby, topaz
with Nu1 (ν1) and Nu2 (ν2) Coronae
magnitude difference, and separation.
with sapphire, diamond with turquoise, or
Its 4.8-magnitude primary also glitters
opal with amethyst, sparkling with all the
Borealis. They're so widely separated
yellow-white, but the 7.4-magnitude
nuances of the rainbow.
they can be individually seen with the
companion north-northeast wears a
unaided eye if your sky is dark enough
nice golden hue.
his charming description of double
On the opposite side of Corona
glows. A pair of binoculars will easstars was penned by Camille FlamBorealis, we ﬁnd the constellation
ily reveal their colors. Through 12×36
marion in his 1880 book, Astronomie
Hercules, home of the pretty double
image-stabilized binoculars, the
Populaire. These glittering gems of the
night sky are treasures that anyone with separation between the stars is
Kappa (κ) Herculis. The stars
extremely wide. I see Nu1, the
the desire to observe them can acquire.
are quite similar in hue, the
When viewing stars, color perception northern star, as an orange
primary deep yellow while
is a peculiar and very individual thing.
the companion shades a
ember, while Nu2 shines a
The ability to differentiate colors varies
skosh more toward yellowslightly yellower orange.
from person to person. Many men are
orange. They're widely split
As you might suspect with
colorblind to some degree. Women can
through the 130-mm scope
such a spacious relationgenerally distinguish ﬁner shades of
at 23×, with the 6.2-magcolor, but they often perceive a greater
companion northu Color perception varies greatly
from observer to observer. The author
color shift between one eye and the
northeast of its 5.1-magnitude
saw both components of Sigma Coronae
other. We all experience contrast illuprimary. You'd suspect two bright
Borealis as yellow through her 130-mm refracsions. When a deep yellow-to-red star
only 27.3″ apart on the sky would
tor at 37×. Jeremy Perez, observing with a
sits next to one that's not strongly colbe
bound, but in this case,
6-inch reflector at 240×, saw the secondary as
ored, we tend to see the companion as
they're not. Kappa is merely an optical
a reddish purple.
J U N E 2 018 * SK Y & TELESCOPE
CORON A E BORE A LIS: POSS-II / STSCI / CA LTECH / PA LO M A R OBSERVATORY;
SIG M A CORON A E BORE A LIS: JEREM Y PERE Z