The Three Great Nebulae

4 Nov 2016

Little to me is more wondrous than looking at the silvery glow of nebulae churning gas and dust into newly-minted stars. From the nebulae that appear as nothing more than ghostly apparitions to the three colossal star-birth nebulae visible in our skies, I can’t think of any grander sight in all of nature than the birth of new stars out of a dark cloud of interstellar gas and dust.

One of the the most sublime experiences of living in the southern hemisphere is that a few languid slews of the telescope allow one to see all three of those mighty star-birth nebulae: the Great Orion Nebula… the Carina Nebula… the Tarantula Nebula.

Each so magnificent; so different; so astonishingly beautiful; so cosmically grand.

I’ve observed these nebulae countless times but last night was in the quantum leap category of observations. Not only because I’m observing from these steady Bortle black skies, but also because the night before last monstrous black clouds had come boiling up over the horizon bringing with them thunder, lightning and the Kalahari’s first rains (albeit only a few millimetres). The rain was glorious. The transparency after the weather system had moved on just after midnight last night… we’re talking nirvana: transparency as I’ve never experienced it.

It was the perfect conditions for exploring the three great nebulae.

Observations

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

The Great Orion Nebula

I’ve always thought this magnificent nebula looked like a gossamer gull, but no longer. About a week ago I was working at my desk when my hind brain perceived a strange hush had fallen outside. No birds singing, no ground squirrels scurrying around, no shaggy hyrax shambling through the grass.

I walked outside to an extraordinary sight: fourteen white backed vultures circling on a thermal right above me, some mere dots against the sky, some incredibly low, giving me a rare sort of naked-eye binocular view. And then, in what was certainly a once-in-a-lifetime experience for me, one of the vultures swooped down low and checked me out in a slow flyover, gliding silently a few metres above me on his enormous wings (how cool is it to be checked out by a vulture!!) and when he re-gained altitude I heard the equivalent of an avian sonic boom… a mighty flap of his mighty wings.

Looking at the Orion Nebula last night reminded me of the vultures. Naked eye, a fuzzy dot against the black sky. In binoculars, a glowing bird-shaped mist holding steady on some celestial thermal. In the telescope, a gossamer vulture soaring above me; its mighty wings sweeping back into a broad feathery tail that entangles a host of dim stars.

The detail was astounding; a beautiful painting of light and gradations no photograph can capture, and few words can describe; simply an extraordinarily personal view as the vast nebula’s photons streamed into my eye after journeying for 1,500 years through our galaxy.

And when I descended into the vast cavern carved out by the hot young stars of the Trapezium, I felt like I was actually inside that brightly lit cave, poking nosily around the stars of the Trapezium, all six of which showed as razor-sharp diamonds glittering against a background of almost transparent grey silk.

And most exciting of all, the edges of the cavern appeared tinged with rust – touches of delicate rust flecks here and there, as if the cavern is starting to corrode like an earth-bound can tossed negligently out into the veld.

Astronomy writer Walter Scott Houston said of the Orion Nebula, “No amount of intensive gazing ever encompasses all its vivid splendour”, and he is right.

Carina Nebula

If I ever design a workable time machine, I’m taking my 16” Dobsonian back to 1750s Cape Town and giving Nicolas Louis de Lacaille a look at the nebula he discovered. The detail he saw in the Carina Nebula through his 0.5-inch refractor is simply astounding, and I can’t imagine what his eyes would see through a 16″ telescope.

To me the Carina Nebula is the supreme nebula in our skies, vultures notwithstanding. Naked eye it is the brightest patch in the southern Milky Way, a large frosty patch in a rich star field. In binoculars it’s a fabulous sight – a beautiful glowing cloud of silky nebulosity cut across by a dark lane of cosmic dust that divides the nebula into one-third, two-third portions. But in the telescope it is preposterously beautiful… a billowing three-dimensional cloudscape, its raggedy outer edges building up out of the surrounding sky, all those obscure dust clouds, the astonishing radiance of the central masses bifurcated by the colossal forked dust lane, that gorgeous scattered cluster Collinder 228, rich little Trumpler 16 which contains Eta Carinae, the mysterious little smudge of the Keyhole Nebula, and all the other glittering stars that adorn this astonishing nebula.

The nebula’s piece de resistance is the tiny intensely orange little Homunculus – the bipolar shell of gas and dust that surrounds that amazing time bomb, Eta Carinae, and that was formed after the great 19^th century explosion witnessed by John Herschel when he was in Cape Town.

When I read his entries about the beginning of Eta Carinae’s great explosion in 1837 in my copy of Herschel at the Cape – the Diaries and Correspondence of Sir John Herschel, 1934–1938 – and look at the photo taken by Hubble 171 years later my brain boggles trying to envision the magnitude of what he actually witnessed:

Tuesday, December 19, 1837: “η Argus is now hardly inferior to α Centauri, but it is inferior. Very like in colour. It is much brighter than Rigel. Procyon is left out of all Comparison α is to η like a * 2m to one of 1st” (Tuesday, December 19, 1837)

Wednesday, December 20, 1837: “ η Argus is not so bright as α Centauri but it far exceeds β Orionis now at nearly same alt. It is much nearer to α Orionis than to β Centauri, α Orionis is small and Procyon trifling compared to it. NB α Centauri is low. As to α Crucis, β Centauri etc these are out of all question.”

Friday, December 22, 1837: “η Argus is far superior to Rigel… and decidedly exceeds α Centauri – but α is lower by far and there is also haze in the sky so comparison not fair – yet I perceived no haze in or near α . – η is now evidently going on to rival Canopus.

Sunday, December 23, 1837: “η Argus is larger than α Centauri, and begins now to approach Canopus – there is not so much diff bet Canopus & η and η and α Cent.”

And here I am, 179 years later, seeing the tiny soft hazy lobes, intensely orange, with post-explosion Eta Carinae buried within them. I read ages ago that Bart Bok’s wife – she was ailing at the time and they were at some do at some planetarium – told Bart that when she was gone, she was going to the Carina Nebula so she could have a front row seat and watch stars forming right before her eyes. I sincerely hope that in the distant future I am sitting beside her… not only to watch stars form but to watch this one star blow itself to smithereens.

Tarantula Nebula

When I was living in Kleinmond in the Western Cape, an eleven year old boy named Isaac came to look at the stars. He had never looked up; he knew nothing at all about the stars. When his mother arrived hours later to pick him up, I asked him what had been the most amazing thing he had seen, and this little boy who had arrived knowing nothing, gave my question more consideration than any adult ever has and after a long silence, replied, “Definitely seeing a nebula in another galaxy.”

Then he added, “And knowing that I am just a star with a people name.”

Well, I have to agree with him on both counts.

And a nebula in another galaxy is one of the most amazing things to see, especially one so vast that from 160,000 light years away it fills the FOV with its unmistakable shape.

Like the other two great nebulae, the detail in the Tarantula is astounding, a fantastic landscape of dramatic caverns, ridges and great loops of billowing cloud, brightly lit regions, dark dusty lanes and distinct entangled filaments, as well as ghostly smudges and threads and the silver sparks of starlight.

Without a filter the nebulosity is spectacular! With the UHC filter the radiance of this exquisite object is indescribable! It shimmers with every gradation of nebulous light and displays incredible depth and detail. Even with the filter its heart blazes with NGC 2070’s stars surrounded by an unsurpassed display of bright loops and arcs, streaming lanes of nebulosity, and dark voids. The 3-D effect is phenomenal; the ridges incredibly sharply defined and the rifts and ravines thrown into varying degrees of shadow. The dark voids resemble deep black lagoons surrounded by vast bright cosmic coral reefs with dramatic edges and filaments that curve and branch, and here and there jut back into the inky darkness.

Tendrils of interwoven nebulosity lead the eye outwards from the Tarantula. Some eventually fade away into the surrounding sky, while others lead you to more treasures. A web of tendrils streams out from the southwestern side of the Tarantula, leading to the supernova remnant N157B then further southwest to the superbubble 30 Doradus C. The southern and western tendrils lead one towards the gigantic supergiant shell LMC 2. And one tendril, swirling like a waft of smoke, leads northwards to NGC 2069.

Because out here there is no sense of being rushed by the approach of inclement weather, I am in the happy position of being able to examine an object (or three) as long as I want, but even so I was surprised when our friendly neighbourhood star brought a glow to the eastern horizon and an end to this unforgettable journey among three mighty nebulae.