This is a collage of the Top 9 globular clusters in the southern hemisphere skies.

Of the group, only Omega Centauri and Messier 22 can be observed from northern latitudes, and then not well as they lie low in the south for many observers. As such, northerners consider the Great Hercules Cluster, Messier 13, a superb target. But it pales in spectacle compared to almost all the globulars here. The best deep-sky objects are in the austral skies!

All the images were taken with the same telescope at the same focal length and with a similar set of exposures, to allow a ready comparison between the clusters' sizes and appearances.

Some, like 47 Tucanae and NGC 2808, are richer than the others with dense bright cores. In the classification scheme devised by Harlow Shapley and refined by Helen Sawyer Hogg and Henrietta Swope, they are Concentration Class III and I respectively, on the scale that runs from Roman Numeral I (most densely packed) to XII (loosely concentrated).

Examples of the other end of the scale shown here are NGC 3201 and NGC 4372, at Class X and XII, respectively. They appear visibly looser to the eye and camera, with fewer stars distributed more evenly across their disks.

The central object in this collage, fittingly so, is in a class by itself. Omega Centauri, aka NGC 5139, is so large and rich it is classified as a dwarf galaxy, or at least the core of an ex-dwarf galaxy. It is the largest globular in angular size in our sky (it is large even in binoculars), but it is also intrinsically the largest Milky Way globular known, at 150 light years across. Within its volume is an estimated 10 million stars — it would never be night on any planet in Omega Cen!

47 Tucanae is second only to Omega for visual spectacle in the eyepiece of any telescope, though many observers consider it the better of the two globulars, with its dense core that can exhibit some color.

NGC 6723, while technically in Sagittarius, lies next to the complex of bright reflection and dark dusty nebulosity in Corona Australis, which adds the blue glow in the frame corner here.

There are certainly other fine globulars down under that I've not included in this collage, such as Messier 4 in Scorpius and NGC 288 in Sculptor. Even NGC 362 right next to 47 Tucanae is a fine target, but is overlooked in the shadow of its glorius companion.

All these globulars lie in the same sector of the sky surrounding the galactic core, as they orbit the center of our galaxy. Indeed, their concentration in that direction in our sky was the clue that led astronomers like Shapley to realize the Sun and Earth do not lie at the center of the Milky Way.

But exactly how and when globulars form is still a matter of debate. They seem to be a by-product of galaxy formation or perhaps galaxy collisions. Our Milky Way is accompanied by about 160 known globulars. These are among the best of the lot!

North is up on all the frames. The objects are presented in order of increasing Right Ascension, i.e. from west to east, across the sky, from the westernmost (47 Tuc) at upper left, to the eastermost (NGC 6752) at lower right.

Technical:
All images taken remotely in 2024 at the iTelescope Observatory at Siding Spring, NSW, Australia, using the T33 telescope, a 12.5-inch f/9 Ritchey-Chretien reflector made by RCOS, on a Paramount ME mount, and equipped with an Apogee Alta U16 CCD camera with 9-micron pixels. All images are from monochrome sub-frames taken through clear Luminance, and Red, Green and Blue filters to create a full-color image in processing in Photoshop. Exposures were 2 minutes for L and 4 minutes each for R, G and B subs.

Tags:   2024 47 Affinity Ara Carina Centaurus Color EFX Concentration Class June LRGB M22 Median filter Messier 22 Musca NGC 104 NGC 2808 NGC 3201 NGC 4372 NGC 5139 NGC 6397 NGC 6723 NGC 6752 NoiseXTerminator ON1 NoNoise Omega Centauri Pavo Sagittarius Shapley-Hogg Classification StarShrink T33 Tucanae Vela classification globular globular cluster iTelescope morphology remote telescope southern star cluster types

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The waning last quarter Moon rises in conjunction with the Pleiades star cluster, aka Messier 45. here just having risen out of a band of clouds at the bottom of the frame that was just above the northeast horizon. The Moon was only 2 or 3 degrees above the horizon when I shot this.

This was the evening of August 25, 2024. Earthshine is just visible on the "dark side of the Moon." And yes, the sky really was this colour, as this field was so low and it was lit by moonlight reddened by atmospheric absorption.

Taken from home in Alberta at latitude 51° N.

Technical:
This is a blend of 10 exposures taken in quick succession, from 15 seconds for the stars and base sky, to as short as 1/30-second for the lunar disk, blended with Lights1 luminosity masks created with Lumenzia extension panel in Photoshop. The exposure blending results in an image that better resembles what the eye could see in the scene with such a high dynamic range in brightness.

The Canon R5 was at ISO 1600 and on the Astro-Tech 90CFT refractor telescope at f/4.8 for a focal length of 430mm. It was on the Astro-Physics Mach1 mount tracking the sky at the sidereal rate. Thus the blurred clouds. Finishing-touch Orton-style glow and stellar diffraction spikes added with Nik Color EFX and AstronomyTools actions.

Tags:   2024 90CFT Astro-Tech AstronomyTools August 25 Conjunction Earthshine Lumenzia M45 Moon Moonrise Nik Color EFX Pleiades Rising Waning absorption clouds exposure blend last quarter luminosity masks orange reddening star cluster star spikes telescope third quarter

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Low altitude satellite tracks cover nearly every subframe from this 19 image set acquired over two nights for Comet 13P Olbers passage by M64. Photographing the night just after dark or just before dawn becomes more and more problematic with each passing day. 13P is visible for only minutes after the sky becomes dark enough and the satellites still catch the light. The tracks are faint but still ruinous to the "pretty picture"

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Questar telescope and Nikon Z7II

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