Sky & Telescope - USA (2019-11)

Open Clusters

66 NOVEMBER 2019 • SKY & TELESCOPE

M93

King 24

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PUPPIS

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the images in July and September 2018 and March 2019, all

from New Ringgold, Pennsylvania. He used two telescopes,

an 11- and a 12.5-inch, and applied 60-second exposures to

acquire the images via a CCD camera. For each image, 20 or

more exposures were collected and stacked to reduce noise,

and luminance, red, green, and blue fi lters were applied to

reproduce color. The short exposure time was chosen to simu-

late what a visual observer would see. Each image has a bar

representing 5 arcminutes superposed.

One thing to bear in mind is that it’s obvious that the

camera is much more capable of recording fainter stars and

resolving the cluster than the observer’s eye. The camera can

integrate light and make objects stand out better than large-

aperture telescopes. However, as experienced visual observers

have learned, increasing the magnifi cation can increase the

contrast of the fainter objects, and the eye is better able to

distinguish them from the background. As planetary scien-

tist and imaging-instrument

developer Roger Clark states:

“The eye is more sensitive

to fainter, lower contrast

objects when they appear

larger to your eye.” Cells in

the visual system respond to

sudden changes of bright-

ness but do so poorly when

the illumination is gradual.^

Although the aesthetics

of most of the King open

clusters may not overwhelm

the observer, the challenge

of fi nding them and sepa-

uKING 25 In northern Aquila, King 25 is fairly faint, and I can just

about see it. I can possibly snag three stars with averted vision. I fi nd

it hard to reconcile the numbers and brightness of its Trumpler clas-

sifi cation; I would probably consider it to be more like II1p.

Mv = unavailable | S = 5′ | No. = 40 | Tr = III2m | Mag. = 272×

qKING 23 We head into Monoceros for this cluster, also called

Czernik 28, which appears as a gentle arc of about 5 stars that seem

to cup some haziness. King 23 is in the same low-power fi eld as

Berkeley 37, a slightly more obvious open cluster visually.

Mv = unavailable | S = 5′ | No. = 20 | Tr = III2p | Mag. = 337×

qqKING 24 In Puppis, this cluster — another that also has a Cz-

ernik designation, Czernik 32 — comprises two “bright” stars with a

faint hazy glow near a delicate string of stars.

Mv = unavailable | S = 3′ | No. = 30 | Tr = II1m | Mag. = 337×

Monoceros

Puppis

Procyon

King 23

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CANIS

MINOR

MONOCEROS

7 h 30 m

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7 h 20 m 7 h 10 m

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