Geodes are the mysterious treasure-boxes of the geological world. Undistinguished round rocks from the outside, they reveal a cavity in the middle filled with beautiful crystals when they are broken open. The rough exterior of a geode gives no indication of the treasures held within its core – its composition is only discovered when it is cracked open – and the size and formation of the crystals and the different shades of colour make each geode unique. From those literally bursting at the seams with gorgeous crystals to those that contain the most delicate outcropping of tiny crystals, no two geodes are alike.

One may be forgiven for wondering what geodes have to do with one of the Large Magellanic Cloud’s rich collection of superbubbles! But peering into the heart of a superbubble is like peering into the heart of a celestial geode… instead of a bubble of rock with fabulous crystalline treasures in its cavity, a superbubble’s cavity is surrounded by rich H II regions and contains at its heart the most gorgeous starry treasures. And like terrestrial geodes, from those literally bursting at the seams with gorgeous stars to those that contain the most delicate outcropping of stars, no two superbubbles are alike! And as a dedicated rockhound, I can assure you that this glorious superbubble in N158 looks just like any one of the geodes in my collection!

A superbubble full of stars… and a geode full of crystals

16″ at 228x: LH 104 = NGC 2081 is a superb star cloud, dominated by B-class supergiants, and lying in the star-filled cavern blown by the lives and deaths of its massive OB members. It is ~5′ in size, and surrounded by a soft and raggedly uneven wash of brightish nebulosity in an oddly triangular shape. Close to twenty stars are resolved, set against the beautiful glow of unresolved starlight. Three Wolf-Rayet stars are among the star cloud’s treasures – mag 13 Brey 94, mag 13.1 Brey 95, and mag 12.2 Brey 95a. And a very special treat lies on the northeast side – mag 11.9 star HD 38489 is an extreme luminous blue variable, 16″ at whose spectrum is similar to that of our very own Eta Carinae!! And looking like nothing more than a slightly bloated mag 11.3 star, HD 269936 is another of the Cloud’s numerous compact clusters, consisting of 14 components. It seems inconceivable that 14 stars are crammed into that point of light that looks very little different to any other mag 11 star!

The nebulosity surrounding LH 104 has a great response to the UHC filter – the soft, ragged wash is revealed as a beautifully bright (but still ragged-looking) nebulous glow that has the most fabulous shape – resembling a hybrid between a circle and a triangle! (On a geological note, most geodes are also oddly hybrid shaped.) The northwestern side is quite faint – an uneven patch of very soft and translucent nebulosity, and with no edges as it simply dissolves into the starry background. The northeastern and eastern sides are very attractive – they are beautifully brighter, smudgy strands and patches scattered along the length of soft and translucent nebulosity.

The nebulosity is brightest and most detailed along the southern rim. It looks like a bright, somewhat warped and tattered ribbon of nebulosity against the faint overall background haze. Its brightest section is BSDL 2722, a bright knot that looks as if it is pushing the fainter surrounding nebulosity into the star cloud, for there is a lovely hazy headland of nebulosity that bulges northwards into the star cloud. A bright strand of nebulosity sweeps away from the bright knot towards the east and in fact, the whole southern portion has a number of streaks and wisps within it. Lovely!!

16″ at 228x: LH 101 = NGC  2074 is gorgeous!! It is a large, beautifully bright semi-circular chain of stars, open to the southwest and surrounded by N158C’s bright and large arc-shaped nebulosity. The chain of stars is marked by bright stars at either end. On the northwest side of the chain lie two bright and rare stars oriented SW-NE (50″ separation). Mag 10.7 HD 269927 (the northeastern star of the two), is a pair of OB stars (TDS 3273 = 12.0/12.2 at 1.8″.) And the southwestern star of the two is a mag 12.5 Wolf-Rayet star, Brey 91. And if these two beauties aren’t enough, the mag 10.3 star to Brey 91’s southwest is A0-class HD 269923, the lucida of the association. The bright star on the southwest end of the chain is mag 12.5 CPD-69 471, an O3-class supergiant. And between these bright stars, at 333x ten fainter stars are resolved, set in a lovely pool of unresolved starlight.

The arc-shaped nebulosity is stunning! Elongated 4.0′ x 2.5′ E-W, without a filter it is bright and uneven and has a gloriously pearly aspect to it. It has an excellent contrast gain with the UHC filter: it is bright, dense, beautifully uneven, and full of shifts in brightness. A small but brighter knot of nebulosity lies in the gorgeous glow within the northeast side of the arc. The nebulosity’s edges are very irregular and fade rapidly into the background.

16″ at 228x: The small dark streak that cuts into the nebulosity on its eastern side is known as the “Seahorse of the Large Magellanic Cloud”. It is a gigantic dust pillar structure roughly 20 light-years long; condemned to disappear over the next million years as more stars in the cluster form, their light and winds slowly blowing away the dust pillars. What an object to see!! But it remained unseen by my eyes and equipment despite a long and diligent search. (Who can’t love the enchanting little seahorses that inhabit Earth’s seas… and to observe one in the LMC would have been enchanting, but alas, the vagaries of astronomy dictated not.) I wonder if big amateur telescopes will pick it up, or is it just a candidate for astrophotography?

The Seahorse of the LMC. In 2008 Hubble took this dazzling photograph to commemorate completing its 100,000th orbit in its 18th year of exploration and discovery! The roughly 100 light-year wide region is a firestorm of raw stellar creation. Credit: NASA, ESA, and M. Livio

16″ at 228x + UHC filter: It is astonishing to observe a star in the first phase of its life, having evolved past the protostar stage (i.e. is shining by way of internal nuclear reactions) but that is yet to enter the main sequence of the Hertzsprung-Russell diagram! It appears as an extremely small, faint droplet of dimly glowing nebulosity with crisp edges.

16″ at 228x + UHC filter: This emission object appears as a small, smudgy glow of pale nebulosity with crisp edges.