Sky & Telescope - July 2021 - 33

X BONUS NEBULOSITY M45 is the brightest of the Messier clusters
and among the five closest clusters to Earth. Long exposures reveal
bluish reflection nebulosity as well as the brownish dust clouds that
permeate the entire region.

appealing as an imaging target. It shows a distinctive triangle
of bright stars standing out from the rest of the cluster.
Our ﬁnal stop is NGC 2419 in Lynx. This tight globular
is one of the loneliest-looking deep-sky objects I've imaged.
The ﬁeld in which NGC 2419 resides contains relatively few
stars, and the cluster has a small, distant appearance. Being
so much further away from us than its northern cousins like
M13, NGC 2419's star colors are mainly reddish hues, and
the core is well resolved.

Imaging Strategies
When it comes to imaging star clusters, it's quite literally all
about the stars. Perfect focus is essential to make the stars
as sharp and contrasty as possible - poor focus makes them
appear puffy and bloated. I refocus the telescope frequently as
the temperature drops during my imaging session to ensure I
retain the smallest stars. It's also easy to overexpose very dense
clusters (particularly globulars), so I try to ﬁnd the exposure
that best reveals the fainter cluster members without turning
the brighter core region into an over-exposed blob.
For clusters with a wide range of brightness, or clusters
embedded within bright nebulosity (such as θ Orionis in
M42), consider using HDR techniques for acquisition and
processing. This involves capturing and later blending short
and long exposures to reveal detail in both the brightest and
faintest regions in a single image. Keep in mind that too
much brightness suppresses the perception of color, robbing
the brightest stars of their beautiful hues, so you may need
to increase the saturation settings while also decreasing the
brightness of the highlights in your picture.
Open clusters are also great tools for evaluating an imaging
system's performance. I often use them to conﬁrm optical performance in my imaging systems - star images quickly reveal
problems with camera tilt and collimation, and they help me
conﬁrm the proper spacing between a ﬁeld ﬂattener and my
camera's sensor. Stars emit light across the visible spectrum,
rather than at a few speciﬁc wavelengths, so clusters aren't
ideal targets for narrowband ﬁlters, including the multiplebandpass ﬁlters often used with one-shot color cameras.

Go for Galactic Glitter
Star clusters come in a wide variety of shapes, sizes, and
brightnesses. Some are surrounded by a variety of beautiful
celestial scenery, which creates a wide range of compositional
choices. Next time you think the Moon is too bright for deepsky imaging, remember that many of these sparkles in the
dark can show through even strong light pollution. So, give
them a shot - you won't be disappointed!

RON BRECHER photographs the night sky from his backyard observatory in Guelph, Ontario.

Select Star Clusters for
Mid-Northern Latitudes
Object

Constellation

Size

Dec.

M44

Cancer

1.7°

08h 40m

+19° 59′

M67

Cancer

30′

08h 51m

+11° 49′

M53

Coma Berenices

12′

13h

NGC 5053

Coma Berenices

8′

13h 17m

+17° 42′

M13

Hercules

20′

16h 42m

+36° 28′

Canes Venatici

16′

13h 42m

+28° 23′

21′

15h

19m

+02° 05′

36m

-23° 54′

Serpens Caput

13m

+18° 10′

M22

Sagittarius

33′

18h

M10

Ophiuchus

19′

16h 57m

-04° 06′

M12

Ophiuchus

14′

16h 47m

-01° 57′

M14

Ophiuchus

10′

17h

M11

Scutum

14′

18h 51m

-06° 16′

NGC 6791

Lyra

10′

19h 21m

+37° 46′

M56

Lyra

7′

19h 17m

+30° 11′

7′

20h

31m

+60° 38′

24m

+61° 35′

NGC 6939

Cepheus

38m

-03° 15′

Cassiopeia

12′

23h

NGC 884

Perseus

30′

02h 22m

+57° 07′

NGC 869

Perseus

30′

02h 19m

+57° 09′

16m

+58° 49′
+58° 20′

M52

NGC 436

Cassiopeia

5′

01h

NGC 457

Cassiopeia

12′

01h 19m

M45

Taurus

1.8°

03h

47m

θ Orionis

Orion

30″

05h 35m

-05° 23′

+24° 07′

NGC 1981

Orion

25′

05h 35m

- 04° 26′

35m

- 05° 55′

NGC 1980

Orion

14′

05h

M37

Auriga

15′

05h 52m

+32° 33′

4.7′

07h

+38° 53

NGC 2419

Lynx

38m

Angular sizes are from recent catalogs. Right ascension and declination
are for equinox 2000.0.

s k y a n d t e l e s c o p e . o r g * J U LY 2 0 2 1

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Sky & Telescope - July 2021

Table of Contents for the Digital Edition of Sky & Telescope - July 2021