M 72

Globular Cluster M72 (NGC 6981), class IX,

in Aquarius

Right Ascension	20 : 53.5 (h:m)
Declination	-12 : 32 (deg:m)
Distance	52.8 (kly)
Visual Brightness	9.3 (mag)
Apparent Dimension	5.9 (arc min)

M71 (class X-XI) and M56

(class X) are even less concentrated.

M72 is approaching us quite rapidly, at 255 km/sec, and has the considerable

number of 42 known variables, mostly RR Lyrae stars.

Its diameter is a bit more than 90 light years.

According to the Deep Sky Field Guide to

Uranometria 2000.0, the brightest star in M72 is about 14.2 mag, while

Kenneth Glyn Jones, quoting Helen Sawyer Hogg, gives the average of the 25

brightest stars as 15.86. The horizontal branch level magnitude is 16.9

(Uranometria 2000.0).

There are several ways to locate M72:

Either find 4.5-mag 3 Aqr and 4-mag Epsilon Aqr from Delphinus; M72 is 3 deg S,

1.5 deg E of Epsilon. Or locate M73, the group of four

stars, from Nu Aquarii; then M72 is 1.5 deg E and little N. Or find it 9 deg E

of 4-mag Alpha Cap.

M72 is a pale nebulous patch of light, very small and of grainy texture in a

4-inch, which shows only the 2′ diameter core region. Larges scopes show it

larger. This globular is of notable even brightness, fainting very gradually

to the edges. It is hard to resolve in amateur telescopes; in the 8-inch, only

the extreme edges show suspicions of resolved stars. A close pair of stars is

situated to the south of this cluster.

---

Hartmut Frommert

([email protected])

Christine Kronberg

([email protected])

Last Modification: 30 Jul 1999, 22:40 MET