Sky & Telescope - USA (2020-01)

56 JANUARY 2020 • SKY & TELESCOPE

the primary. The sparse cluster shows

11 stars and is elongated north-south

about 6½′, while the nebula is a little

longer and extends farther east of the

cluster than west.

Stock 8 looks much richer when

viewed through my 10-inch refl ector at

118 ×. I see 35 to 40 moderately bright

stars loosely strewn across 11′ of sky. IC

417 engulfs the more crowded regions

of the cluster and covers about 8′.

Viewed through my little refractor

at 47×, IC 417 shares the fi eld with

the smaller but much more obvious

nebula Sharpless 2-237. The 11th-

magnitude star nestled in its heart is

almost overpowered by the glow of the

nebula, but it shows up much better

when I increase the power to 87×. It

sits at the northwest corner of a 3½′

box that it forms with three dimmer

stars. The nebula is very bright close to

its star and fades sharply outward to a

diameter of perhaps 3½′.

NGC 1931, the cluster associated

with Sh 2-237, begins to emerge in my

10-inch scope at high power. The bright

star is shown to be a quadruple, with

Chariot of Stars, Clouds of Fire

Object Type Mag(v) Size/Sep RA Dec.

Melotte 31 Asterism — 135 ′ 5 h 18.2m +33° 22′

IC 410 / NGC 1893 Nebula / cluster 7.0 40 ′ × 30 ′ 5 h 22.6m +33° 22′

Espin 332 Double star 8.9, 9.5 14.8′′ 5 h 21.4m +33° 23′

AE Aurigae Bright Star 6 — 5 h 16.3 m +34° 18 ′

IC 405 Bright nebula — 30 ′ × 20 ′ 5 h 16.6m +34° 25 ′

Cheshire Cat Asterism 3.9 90 ′ 5 h 27.3m +34° 52′

Stock 8 / IC 417 Cluster / nebula — 15 ′ 5 h 28.1m +34° 25′

Sh 2-237 / NGC 1931 Nebula / cluster — 7 ′ 5 h 31.4m +34° 15′

Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture

and magnifi cation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

JANUARY 2020 OBSERVING

Deep-Sky Wonders

the three brightest members arranged

in a tiny triangle and the fourth

component to their northeast. Several

additional stars straggle south through

west-southwest of the group.

The three clusters highlighted here

are among the youngest visible in the

sky. Their eldest members are a mere 4

million years old, and starbirth within

them is still ongoing.

¢ Contributing Editor SUE FRENCH

wrote this column for the January 2010

issue of Sky & Telescope.

pOpen cluster Stock 8, together with the surrounding emission nebula IC 417, is visible in

small telescopes under moderately dark skies.

uSharpless 2-237 is so bright that it almost hides NGC 1931, its embedded star cluster.

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