Sunday, 28 January 2018

K 2-1: Never be discouraged

I've written this already a couple of times before, but never be discouraged by a strange object denominator. There's so much more to discover beyond the classic Messiers and NGCs and often you'll be amazed by what you find. Take this strange planetary nebula, for example. Its name is Kohoutek 2-1, after its Czech discoverer, and it lies about halfway between Elnath (B├Ęta Tauri) and Iota Aurigae. Although it's obviously not the brightest of planetaries, it immediately leapt out at me when it moved into the field of view of my binoscope. Even more so, I had no difficulties at all noticing that this particular planetary is way out of the ordinary. As you know, planetary nebulae are usually round or elliptical, hence the nick "planetary" nebulae because they look a bit like a planet. This one's a whole different league with its strange lobes and wonderful structures.

I've found very little information about this little nebula, but I suspect that its central star's binary. I did have the impression to have seen a tiny companion which I've also represented in the sketch. This would certainly explain a lot because the gravitational pull and radiation of a companion star would severely disrupt the nebula's shape.

To make the picture even more interesting, the nebula's surrounded by a lovely, loose cluster of tiny stars, denominated "Skiff 3". Again, no other information to be found anywhere. The nebula would be 3,600 light-years distant, but the for the cluster I can only guess that it lies way beyond.

Friday, 26 January 2018

NGC1555: Hind's Variable Nebula

T Tauri is a very young star that's only just emerged from the cocoon of dust and gas in which it was born. Fusion's just ignited in its core but is still unstable. Soon, this star will blow away the dust that's still surrounding it and grow into adulthood as a stable main-sequence star, fusing hydrogen into helium. 

For the moment we're not quite there yet as you can see. The star has a distinct yellow-orangy colour and varies in brightness as fusion still needs to stabilise. The surrounding dust glows in its light, obviously with the same variations as the star. I had the impression that also the nebula appeared slightly yellowish, but that's obviously an optical illusion due to the proximity of such a strongly coloured star. Still I couldn't resist adding a bit of yellow to the nebula too, for artistic reasons and because it renders the illusion at the eyepiece. 

It also seems that this nebula was significantly brighter when it was discovered in the late 19th century. The famous German astronomer Friedrich Struve reportedly found another, similar nebula very close to NGC1555 and this discovery was confirmed by others. Strangely enough, this nebula, which had been catalogued as NGC1554, couldn't be found anymore a decade after its discovery, nor has it been found ever since. Scientists now speculate that it was a transient portion of the same reflection nebula complex. 

T Tauri and its surrounding nebula lie approximately 500 light-years away.


 

Wednesday, 24 January 2018

Procyon

Procyon, bright and yellowish, is the brightest star in the winter constellation of Canis Minor, the small dog, and the eighth brightest star in our sky. Not that it's a big and impressive star as such, but its relative brightness merely originates in its proximity. At a distance of only 11.4 light-years, Procyon is the 14th closest star to our Solar System. Let's say it lies right under our doorstep, in astronomical terms. For the rest it's nothing out of the ordinary, with a mass s.5 times that of our Sun and a diameter twice as big. It also boasts a solar-like corona which it heats up to 1.6 million °C. Procyon's much younger than our Sun though, but after 1.7 billion years it has already depleted its entire hydrogen supply and fusion has started to expand outside of its nucleus. It's preparing to evolve into a much bigger, helium-fusing red giant, which will happen in the next 10 to 100 million years.

Nothing out of the ordinary, you'd say. Yet, this inconspicuous, bright star hides a little secret. It had already been suspected in the early 19th century due to irregularities in the star's proper motion, but it was not confirmed visually until 1896. Procyon is indeed double, the main star orbited by a tiny companion that's extremely difficult to observe. Procyon B lies 4.3 arc-seconds from Procyon A, which should be doable also in small telescopes, but the problem is that A shines 15,000 times more brightly than B and therefore the little one disappears into A's glare. Even with my binoscope I had a really hard time separating the two and I had to wait for that moment of perfect seeing to detect the companion, as I've tried to reflect in my sketch.  

B revolves around A in a highly eccentric orbit which takes it as close as 9 AU (Astronomical Unit - the distance between the Earth and the Sun) and as far as 21 AU over a 40-year period. It's a white dwarf only 30% larger than the Earth but contains 60% of the Sun's mass. Its average density is therefore a whopping two tonnes per cubic inch! Scientists believe that B was once bigger and hotter than A and therefore it evolved a lot faster. When it got older, it evaporated much of its mass onto A, which gradually became the dominant star in the system. We find that A is indeed quite rich in heavier elements, byproducts of advanced nuclear fusion in B. 

No evidence for planets has been found to date and even if there were, they would probably not be suitable to sustain life due to the distortion and radiation of this extreme double star system. However, a large ring of dust has been detected. 

PS: The image doesn't show well in Blogger, but B lies slightly to the bottom-right of A...



Monday, 15 January 2018

Jonckheere 320: Off the beaten path again

Most amateur astronomers prefer to stick to the well-known Messier and NGC catalogues when preparing their observation night as the more exotic ones like Minkowski, Kohoutek, Berkeley and the likes have the reputation of being too difficult for basic, amateur instruments. Nothing, however, could be further from the truth. Yes, there are some pretty invisible objects in those catalogues which even in my big binoscope refuse to reveal themselves. On the other hand, some of these more exotic objects turn out to be surprisingly easy.

Take Jonckheere 320 (J320), for example. It's a small planetary nebula in Orion, almost halfway between Bellatrix and Aldebaran. Actually, it's so small that it was originally mistaken for a double star and it takes as much magnification as circumstances allow you to bring out the details. But searching with an OIII filter will surely make it stand out against the background and I didn't have any difficulties at all finding it. When you then push telescope power to the max, you'll notice that this little gem has a lot of interesting detail on offer. 

Its bright central area boasts a lot of filaments and structures, as is typical for a young planetary nebula in full expansion. I even managed to get a glimpse of its "ansae", puffs of hot gas that are ejected from the central star's poles at the incredible speed of 43km/s. The central area itself rotates at 13km/s which is surprisingly fast. Usually stars tend to rotate slower as they grow older, but in this case the dying star's still driving the surrounding nebula into a fast spin. 

Unfortunately, the central star itself was invisible to me, but this has probably everything to do with its great distance. Measurements differ greatly, as is usually the case with nebulous objects, but 15.000 light-years seems to be the more popular value. This obviously also explains why it appears so small to us. And yet... being so far away and still shining so (reasonably) brightly in our sky... this planetary must really be something extraordinary.

Wednesday, 10 January 2018

The Horsehead

Few objects stimulate the imagination as much as the famous Horsehead Nebula (B33 in technical terms). Its suggestive shape has amazed people ever since its discovery in 1888 and it's become one of the most photographed objects in the sky. Unfortunately, to us, humble visual observers, this extraordinary patch of dust is a daunting target. Yes, I've read all of the reports that say that it was "easy to see in a C8" and I've even seen sketches, observed through a 6" without filters (!), that show it in all of its glory (and almost in 3D-Technicolor too). But are they trustworthy? No, unfortunately not. 

Sometimes, we visual astronomers behave like fishermen who claim to have caught a five-foot sardine. It's not just about showing off, but we also want to convince ourselves that we've really seen a very difficult object, even though it was on the border of visible, or sometimes beyond. Who can blame us? Often we spend many hours trying to find it, peering through that tiny little hole of our telescope's eyepiece until our other eyelid's sore of keeping it shut, our whole body's shivering because of the biting cold, our limbs numb, our noses dripping, our foreheads frosted, our brains begging us to go back indoors and preferably to sleep. Yet, we persevere because we want to find that particular object. It's like a trophy we desperately want to hang on the wall. 

In the case of our beloved Horsehead, which is so incredibly faint that it was hardly visible through my 18" binoscope, things tend to get a little out of hand. A H-Beta filter helps a lot to bring it out and makes this nebula accessible to smaller scopes under dark skies, but don't expect miracles. Given that a pair of these filters'd cost me €400 and that they're only useful on a handful of objects, I preferred to try and find it without. And with success, although it remained extremely faint as I've tried to reflect in my sketch. The background nebulosity, scarcely illuminated by the embedded newborn stars was hardly apparent as a somewhat lighter half of the field of view, compared to the darker left half. Something that struck me much more was the almost total absence of little background stars in that left half. Obviously, the light of background stars is completely blocked by the enormous cloud of dark dust that cuts through the field of view and of which the Horsehead is just a bulge sticking out. Fortunately for us, this peculiar bulge drifts in front of the delicate bright nebula behind it (IC434) and therefore becomes "easily" visible. Well, let's say that I've seen it. This whole area, some 1,500 light-years distant, is but a part of the gigantic Orion Molecular Cloud, a vast region in space where a lot of star formation takes place. Also the Orion Nebula is just a part of this complex. 

Much more evident in the same field of view, is a reflection nebula called NGC2023 (bottom-left on my sketch). Being over 4 light-years across, it's actually one of the largest reflection nebulae in our sky, brightly illuminated by the young and extremely hot giant star that lies within it.