Sky and Telescope - November 2018 - 39

a dim smudge. I thought Hubble VII would be my last globular sighting in the galaxy. But in 2011 a wide-ﬁeld imaging
survey with the Canada-France-Hawaii Telescope (CFHT)
uncovered four new halo globulars in NGC 6822 designated
SC1-SC4. Two years later, three more globulars (SC5-SC8)
were identiﬁed using archival CFHT/MegaCam data. New
globulars and a new challenge!
SC7 (not to be confused with Hubble VII) lies outside
the visual boundary of NGC 6822, 22′ northeast of center,
making a positive identiﬁcation much easier. At 375× in my
24-inch, I immediately noticed a swollen 15th-magnitude
"star" about 6″ to 8″ in diameter. The globular could be held
steadily and seemed to have a brighter stellar nucleus.
SC6 is over a half-magnitude fainter than SC7 and a
much tougher catch due to a brighter 14th-magnitude star at
its north edge. I needed 500×, good seeing, and a healthy dose
of patience to tease out an occasional stellar sparkle.
Hunting globulars in M31 is a popular project for seasoned
deep-sky observers. I've tallied 45 (mostly with an 18-inch)
along with 10 open clusters. Three of the brightest - G76,
G78, and G280 - are close to magnitude 14.3 and readily
accessible in a 10-inch under dark skies. Contributing Editor
Alan Whitman covered these and many more in his article on
M31 (S&T: Nov. 2013, p. 58).

In 1932 Hubble charted 140 nebulous objects in M31
found on 100-inch Hooker telescope plates and tentatively
identiﬁed these as globulars based on "their forms, structure, colors, luminosities, and dimensions." Hubble missed
G1 (also called Mayall II), the most luminous globular in
the Local Group, as it resides in M31's halo, 2.5° southwest
of center at a projected separation of 130,000 light-years.
A kinematic study of G1's nucleus in 2002 using the HST's
Imaging Spectrograph provided strong evidence that it houses
a 20,000-solar-mass black hole.
But is G1 a true globular cluster? With more than twice
the mass of Omega Centauri (the Milky Way's heftiest globular), G1 may be the remnant core of a stripped dwarf galaxy
that was digested by M31 earlier in its history.
I've seen 13.8-magnitude G1 with only an 8-inch scope,
though two 14th- to 15th-magnitude stars on the west edge
confuse the view at low power. Using 323× in my 18-inch, G1
was easily visible as a 10″ puffball punctuated by a star-like
nucleus, and the two nearby foreground stars form a cute pair
of "Mickey Mouse" ears.
Recently, astronomers have found a cache of new globulars
in the extreme outer halo of M31. Martin-GC1 (MGC1) was
discovered in 2006 during a CFHT/MegaCam survey, a whopping 8.6° south of M31 in the constellation Pisces! A 2009

Extragalactic Globulars & Friends
Galaxy
LMC

Galaxy Type
Irr

# of GCs
16

GC

dIrr

1

RA

Dec.

10.2

05.1m

NGC 1916

10.4

05h

18.6m

-69° 24′

NGC 1903

11.9

05h 17.4m

-69° 20′

Open cluster

8.6-11.5

05h

18.3m

-69° 15′

Variable star

Reticulum Cluster

14.7

04h

36.2m

-58° 52′

NGC 121

11.2

00h 26.8m

-71° 32′

24.1m

-72° 05′

NGC 1835

-69° 24′

Milky Way

SBbc

160

47 Tucanae

4.1

00h

Fornax Dwarf

dSph

5

NGC 1049

12.6

02h 39.8m

-34° 15′

14.1

02h

38.7m

-34° 49′

40.1m

-34° 32′

Fornax 2

NGC 6822

M31

WLM
Sgr Dwarf

dIrr

Sb

8

> 500

Notes

05h

S Doradus
SMC

Mag(v)

Fornax 4

13.6

02h

Fornax 5

13.6

02h 42.4m

-34° 06′

SC 7

14.8

19h 46.0m

-14° 33′

Hubble VII

16.3

19h

44.9m

-14° 49′

SC 6

15.3

19h 45.6m

-14° 41′

32.8m

+39° 35′

G1

13.8

00h

Martin-GC1

15.5

00h 50.7m

+32° 55′

PAndAS-53/54

15.5

01h 18.0m

+39° 15′

dIrr

1

WLM-1

16.1

00h

dSph

4

M54

7.7

18h 55.1m

Milky Way satellite

Milky Way satellite
Milky Way satellite

Local Group Member

Local Group Member

01.9m

-15° 28′

Local Group Member

-30° 29′

Milky Way satellite

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

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Sky and Telescope - November 2018

Table of Contents for the Digital Edition of Sky and Telescope - November 2018
