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CAC's Spaced-Out Challenge: Galaxy Guide (Part 3)

Welcome again to the Spaced-Out Challenge, the weekly astronomy post and your guide to the night sky. We are continuing our exploration of the summer Milky Way, and finishing our quick overview of the sights in Sagittarius with a few notable open and globular clusters.

Hop-to guide and a brief overview of objects below the fold.

Let's take a look at the overview chart of this week's targets:

So what are these?

Messier 18

Credit: Jim Thommes
The least distinct of all the open clusters we will discuss, it makes a great hop-through point when touring through the Sagittarius portion of the Milky Way. To it's "north" is the Omega and Eagle Nebulae. To it's "south", the Little Sagittarius Star Cluster. Look for a "patch" of about a dozen stars brighter than the background Milky Way field. An interesting note: some researchers claim it is part of a binary pair of clusters, it's sibling being NGC 6618, found inside the Omega Nebula.

Messier 21

Credit: Jim Thommes
Close by the Trifid nebula is a surprisingly small cluster, M21. It's hot stars are also some of the youngest associated with a cluster at just over 4 million years old. In binoculars it makes a nice balance to the intriguing Trifid.

Messier 23

Credit: Jim Thommes
Arguably the most spectacular of the non-star cloud clusters we'll discuss this week, open cluster Messier 23 is huge, and appears best in binoculars or in a low-power eyepiece through the telescope. This open cluster spans some 30 light years and is unusual in it's lack of diversity in stellar brightness or spectral class. It will appear as a slightly less nebulous patch than the Little Star Cloud. Some describe it as a “star field” due to it's diffuseness.

Messier 24, the Little Sagittarius Star Cloud

Credit: Jim Thommes
A sizable portion of the inner Sagittarius-Carina arm, made visible thanks to another "window" through the closer obscuring dust. While concentrated, it is less so than the central bulge portion discussed in Part 1, so it's stars are easier to resolve. Aim your binoculars and prepare to get lost in a vast swath of stars, not as numerous as in the Great Cloud discussed in Part 1 but enough to leave a deep view and lasting impression on the viewer.

Messier 25

Credit: Jim Thommes
Messier 25 contrasts well with Messier 23, and is located at roughly the same distance from Mu Sagittarius, just in the opposite direction. With a looser appearance, it also enjoys a bit more range in stellar brightness and color.

The Great Globular of Sagittarius

Messier 22 by wiki user Hewholooks
If it was just a bit further north, it would be more well known than the Great Globular in Hercules, being both considerably brighter and larger. The Great Glob of Sag is the third brightest in the sky, behind the massive Omega Centauri and Tucanae 47. It's position leaves it dimmed a bit with the dust and gas of the milky way plane between us, but it's surprising closeness for a globular (only about 10,000 ly away) allows for much of it to clear the galactic fog. An intriguing sight in binoculars, it becomes granular in appearance with even a small telescope.

There are dozens of other intriguing globulars and open clusters in this small region, but we are moving on and up into the southern portion of the Northern Cross next week as we continue our trip through the backbone of the night.

Link up to Guide Part 1
Link up to Giude Part 2
FULP List Link HERE
A quick note: those of you with light buckets or larger SCTs, this upcoming weekend will position the Eagle Nebula highest in the sky and without a glaring moon, so if you were intrigued by last week's guide to finding the Pillars of Creation, now's your chance to test it out.

As always, clear skies to you and keep looking up!