Saturday, May 13, 2017

M71, A Globular Cluster in Sagitta

Many of us have heard of the constellation Sagittarius in the austral skies, but Sagitta is an unknown constellation for many amateur astronomers. Even I can’t remember where it is located in the sky and it is difficult to trace in polluted skies because  it has no star brighter than 3rd magnitude.

Discovered in 1745, M71 is a dim and loose globular cluster located in Sagitta, right between Aquila and Cygnus, two birds that govern the summer skies.  The best way to find M71 is to star hop from the  1st magnitude star Altair , the eye of the Eagle (Aquila). From there, trace a line to the star Sadr in Cygnus and in the first third of that line you will be close to the area where the globular should be.  To the west of the glob, there is an a unique asterism that looks like a tiny arrow made by four stars: 9 Sge (Mag 6.20), HIP97818 (Mag 7.65), HIP97840 (Mag 8.30) and a fourth one of magnitude 9.10.  If you see it, you can‘t miss M71.

It is visible with binoculars under moderate light polluted skies (Surburban skies).  It looked like a ghosty patch next to the asterism decribed below. In fact, one has to use some averted vision to see it. It does not show a definite core, but the whole surface has the same low brightness. I have seen it with my telescope at 100x.  Even at such magnification on 6” of aperture, it  looked like a nebular smudge with about 10 dim stars in it.

Sumer is coming soon so it would be a good time to plan on catching M71!

Clear skies,


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