Ara’s Gorgeous Globular Clusters

NGC 6397 ARA — *The heart of globular cluster NGC 6397. Image credit Hubble*

1 Sept 2016

Globular star clusters are among my favourite deep-sky objects. These beautiful swarms of ancient stars are among the most stirring and beautiful sights in our skies. They are full of wondrous light and a sense of movement.

Their wondrous light… be it nothing more than a faint droplet of unresolved starlight to one that displays a dizzying chaos of stars radiating out in all manner of arcs and curves and lines and bows and curls, they are all beautiful.

Their sense of movement… more than any other objects globular clusters give me a sense of vast movement. While each globular cluster moves as a whole orbiting in the halo of our galaxy, within the cluster the stars also move individually and randomly – almost like molecules in a gas.

Ara has a beautiful trio of globular clusters, all three of them absolute delights of glittering richness. What an honour it is to see them through a telescope.

Astronomy… I’m so glad I devote so much of my life to this. I wouldn’t have it any other way.

Observations

10″ f/5 Dobs at magnifications of 90x, 144x and 208x

10×50 binoculars

NGC 6397 Globular Cluster

RA 17 40 41.36 Dec -53 40 25.3 Mag 6.8 Size 31′

This globular cluster is an observer’s dream… it is the fourth brightest globular cluster in our skies (Omega Centauri, 47 Tuc and M22 being brighter). It is the second closest globular to the sun (M4 is closer by a paltry 700 light years). It ranks first for brightest stars (10^th mag) and resolvability (its horizontal branch magnitude is 12.9.)

Through 10×50 binoculars it is lovely – a big and conspicuous glow of soft and gentle light, like silk in candlelight. There is a gradual brightening toward the centre, a sort of silkier glow upon a silky glow.

At low magnification, it is a breathtaking beauty. Strings of mixed stars curve away from the core, which itself is absolutely gorgeous… a tight little circular core that is brilliantly bright. The strings of stars taper off into the surrounding field in a way that no other globular does.

There are three lovely orangey stars in the southern region. At medium magnification it is even more gorgeous, a dizzying turmoil of stars exploding outwards. I can see dark speckled dark areas between the strings of stars that spiral out. At high magnification the core of diamond dust resolves into tiny pinpoints that glitter like crushed diamonds.

Herschel mentioned a double star at the northern border, but I forgot to look for it; no matter, another night, another look, another treat.

NGC 6352 Globular Cluster

RA 17 25 29.16 Dec −48 25 21.7 Mag 8.87 Size 9′

A beautiful little cluster. In the 10 x 50 binoculars it is a small, round silvery glow set amongst a lovely backdrop of stars. At low magnification it appears as a bright irregular round hazy glow, not very dense; the frosted look of sand-blasted glass. A hazy opacity of light. An absolutely gorgeous sight against the rich background field.

At medium magnification the glow became a haziness enveloped in a silky glow. At high magnification I could see a beautifully bright core but not a single star resolved in the cluster. There is a hazy granular busyness of stars toward the southwester area, and a hint of grainy glints scattered around the hazy periphery.

NGC 6362 – Globular Cluster

RA 17 31 54.8 Dec −67 02 53 Mag 8.1 B * V m 12.7 HB V m 15.3 Size 15.0’

The only word to describe this beauty is scraggly (although in the binoculars it isn’t scraggly, just a lovely small soft round glow.) At low power it is large and bright, and slowly brightens towards a dense wide core. It has a very bedraggled looking halo, and the whole globular looking as if it is covered in a layer of haziness. Its irregular appearance is very striking.

At medium power the globular is a glorious blaze, with its appealing straggly appearance accentuated. Tiny stars are resolved across the globular, looking like tiny diamonds lying on a bed of diamond dust. High power resolves a host of resolved stars across the core, and out across the scraggly edges and deep into the star-field; some in really lovely arcs and sprays of faint stars. A very unusual string of resolved stars bisects the cluster in a north northwest to south southeast orientation.