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.  

Saturday, 23 December 2017

IC2087: When dust lights up

This may sound a bit odd, but most of our Universe is actually invisible to our eyes. When we look up at the night's sky and admire that mesmerising blanket of millions of stars, we only see things that emit light, i.e. stars and gas clouds that are heated up so much that they start glowing. But this is only a small percentage of all matter that surrounds us. The so-called dark matter is, indeed, invisible because usually we can't see it in a Universe that is essentially dark. 

And yet, every now and then we can catch a glimpse of all the dark dust and gas that's floating through space. When a cloud of this dark matter drifts in front of a bright stellar background, for instance, or when it reflects the light of nearby stars. In the case of IC2087, we observe both.

On the border between Taurus and Auriga there's a gigantic dust cloud, merely 700 light-years distant and denominated as Barnard 22, which blocks the light of all the stars that lie behind it. Just point your telescope in that direction and you'll agree that there are only very few stars to be seen. Even with my binoscope the field of view looked strangely empty. In the middle of all that darkness, however, you may find the bright patch which is the protagonist of this blog post. IC2087 is a reflection nebula, i.e. that this cloud merely reflects the light of stars that are embedded in it. Careful study of this cloud with infrared telescopes has not only revealed its main light source, but also that this nebula contains a lot of embryonic stars. These baby stars haven't really lit up yet and therefore the nebula remains difficult to see, for the moment. But soon fusion will kick in in the star's cores and the gas and dust will be heated up. Probably, within a couple of hundreds of thousands of years, this nebula will become a spectacular stellar nursery, brighter than the Orion Nebula. 


Tuesday, 19 December 2017

PuWe1: Mission Impossible?

There are certain objects which tickle the imagination. You know that they're supposed to be virtually impossible to see with any amateur telescope, and yet the temptation's too strong. No matter how cold it is; no matter having to look for it for over an hour, you simply give in to this nagging crave in your chest and you point your telescope towards a remote corner of the obscure constellation of Lynx. There, in 1980, two Austrian astronomers called Purgathofer and Weinberger, discovered an extremely large, ethereal planetary nebula. It appeared so faint on their original photographic plates that they were unable to present it for printing along with the report of their discovery. Nowadays it has become a challenging object for skilled photographers who manage to capture its delicate structures after many hours of exposure time.

With its extremely low surface brightness of 23.7 mag/arcsec², it has always been deemed impossible for visual observations. But, as loyal readers of my blog will know, impossible is my middle name. What's more, I've got just the perfect instrument for large and extremely faint objects at my disposal. A binoscope effectively collects the same amount of light as a telescope 1,42 times its diameter, but... it offers that amount of light at a much lower magnification. I won't bother you with the technical explanation of all this, but suffice to say that the lower magnification allows to concentrate the frail light of the object on a smaller surface. In other words, you see it more clearly. How clearly? Well, don't get overexcited. After having stared at the right spot for at least fifteen minutes, I daresay that I did see "something". Yes, there was a broken circle of extremely faint nebulosity. It must be the faintest and most difficult object I've ever observed, even more so than oddities like ARO215. Yet, that's exactly the thrill that we faint-fuzzies lovers get from it. You know that it's on the edge of impossible. You're freezing, your limbs are giving in, your eyes are having difficulties to focus. But then... suddenly... that extremely faint arc reveals itself. And it was all worth it.

PuWe1 is one of the nearest planetary nebulae, its distance estimated at under 1,200 light-years. As you might have guessed, it's also very old and has extended over 6 light-years across in the last 20,000 years. Let's enjoy the show while we still can, because it won't be long before this nebula will be gone forever.


Friday, 15 December 2017

IC417: the yellow spider

Rounding off my series about vast and faint nebulae in Auriga, I present you with IC417, otherwise known as the Spider Nebula. Again, it's not an easy object for visual astronomers but with a sufficiently dark sky and generous aperture you should be able to spot it. Although the nebula is a hot star forming region and would therefore benefit from the use of filters, I decided to make my observation without as I shall explain. 

The nebula complex lies somewhere around 7,500 light-years away, in the outlying Perseus arm of our galaxy. As I said, it is another giant stellar nursery in the heart of which we find a lovely, somewhat elongated cluster of young stars, denominated Stock 8. Interesting to note is that these young stars seem to have different ages, ranging from 1 to 5 million years, which indicates that stellar formation has continued over a long period of time here. 

Now let's turn our attention to the bright, yellow star which appear to be the protagonist of this sketch. As you might have guessed, this star (Phi Aurigae) is much closer to us, at a distance of 450 light-years, and is already visible to the naked eye under suburban skies (mag. 5.05). It is an orange giant (although I saw it rather as bright yellow), meaning that it has evolved off the main sequence and is now fusing helium into carbon and oxygen. Although nearly 300 times as bright as our Sun and 31 times its diameter, it does bear a lot of similarities to our star. For starters, it weighs in at 1.2 solar masses and it has a very similar chemical composition. In fact, it's a perfect example of how our Sun will look like in about 5 billion years, after it'll have consumed all of its core hydrogen.

I guess this is just an optical illusion, caused by the brightness and deep colour of Phi Aurigae, but I had the impression that the nebulosity in its immediate vicinity also had a slight yellowish hue. The sight was so lovely that I wanted to capture it this way, rather than to use nebula filters which make all stars appear blue.

Friday, 1 December 2017

NGC1893 and IC410: surrounded by tadpoles

Just one and a half degrees south-west of IC405, we find NGC1893, a young star cluster that lies embedded in the nebula from whence it originated some four million years ago. Even from its respectable distance of 12,000 light-years it shines with a magnitude of 7.5 and is therefore an easy target for binoculars. 

The nebula itself is quite a different matter. With its petals whirling around a dark centre, it closely resembles the Rosette Nebula, even though it appears much fainter and smaller due to its distance. In reality, this nebula spans over a hundred light-years across, four times the size of the Orion Nebula! From Earth, you need a medium to large telescope in order to see it and special nebula filters help as well. These filters block all light, apart from the very specific frequencies which these kinds of nebulae emit. The result is that the background and the stars significantly darken but the nebula doesn't. Therefore it becomes more visible because you get a lot more contrast. 

With my binoscope I was able to see some very interesting structures around the central void. The reason why the nebulosity disappears at the centre is because it's being blown away by the radiation of the hot, young stars that have just emerged from it. So here you're looking at a star-forming nebula in a somewhat advanced state of its evolution. As more stars are born, radiation and stellar winds increase, expediting the nebula's evaporation into space. 

Another interesting feature about this nebula is that it contains "tadpoles". They're extremely difficult to see with amateur telescopes and also I was only able to see two of the "heads" (scientifically referred to as "Simeis 129" (top) and "Simeis 130" (bottom)). Just left of the cluster's central stars you'll see two little knots in the nebulosity. The "tails", gas plumes that are blown away from these "heads" and eroded by a powerful stellar wind, were unfortunately invisible to me.

Monday, 20 November 2017

IC405 and the runaway star

AE Auriga is a very peculiar giant star. It's radius 7 times solar is quite impressive and its 23 solar masses make it definitely a member of the most massive stars club. But this is not the main reason why this star's so out of the ordinary. What does make it so special is that it travels through our corner of the galaxy (well, 1,700 light-years away) at the breakneck speed of 200km/s! Now, if we take the star's estimated age of 2,2 million years and trace its movement all the way back, we find that it originated somewhere in the vicinity of the Orion Nebula! Until recently it was believed that AE Auriga, with Mu Columbae and 53 Arietis, were hurled out of the Orion Nebula together by some sort of cataclysm, like a supernova explosion or a near collision. However, recent measurements by the Hipparchos satellite reveal this to be highly unlikely and the three runaway stars have most probably different origins, albeit still within the Orion complex of star forming regions. 

Currently, our giant star's travelling through a cloud of gas and dust in the constellation of Auriga, the charioteer, which is reflecting its bluish light. The star's high velocity's causing a bow shock and leaves a trail of hot gas in its wake: IC405, better known as the "Flaming Star Nebula". It does seem as if the star's on fire and emitting fumes, isn't it?