Monday, 24 April 2017

A whale, its pup and the effects of telescope power

Galaxies are huge, swirling entities that consist of hundreds of billions to even trillions of stars. Our solar system lies in one of the spiral arms of a galaxy that we refer to as Milky Way because we see it as the faint, elongated cloud that you can see across the night's sky from a dark place. But there are billions of these galaxies, many of them bigger than our own. One of these bigger galaxies can be found in the constellation of Canes Venatici, the hunting dogs, and listens to the denominator NGC4631. In more popular terms, this galaxy's known as the Whale Galaxy because of its fairly odd shape. We see this galaxy edge-on but unlike ordinary spiral galaxies that are more or less symmetrical either side of the nucleus, this one has a bulge towards one end. The reason for this are two minor galaxies that are pulling the stars and other matter in the Whale in one direction. One of these accompanying galaxies can be seen on the sketch just below the Whale itself: NGC4627, aka the Whale's pup. The other lies exactly behind the big bulge and cannot be observed with ordinary telescopes. The gravitational pull causes great starburst activity in the Whale's bulge, as you can tell by the many bright patches within it. The sketch below was observed at 285x and you can see a myriad of detail.


Now let's increase telescope power to 507x and see what happens. Obviously we can't see the entire galaxy in one and the same field of view anymore as we've zoomed in considerably. The image dims because the light the telescope captures is smeared out over a much larger surface. But will we be able to make out even more details? In this case the image at higher power didn't show me more. Every telescope has a limit, also depending on the brightness of the object, and in case of the Whale Galaxy I had the impression that I had surpassed that limit. A friend of mine commented that on the high-power sketch there were still more details to be seen, and perhaps there were also at the eyepiece. Another interesting thing to note is that these two observations were made a month apart, so the high-power sketch was observed with a fresh mind, not influenced by my other sketch. But the 285x view looked a lot more pleasing and I didn't have to peer as much to see all the details as I had to do in the dim 507x view. 

Astronomers call this the "sweet spot" of a telescope. It coincides with an exit pupil somewhere between 1 and 2 millimetres, or in other words the image that comes out of the telescope's eyepiece has a diameter of 1 to 2 millimetres. Or again in other words, you'll find the sweet spot of your telescope with an eyepiece with a focal length that's one to two times the focal ratio of your telescope. If you have a telescope with a focal ratio of f/5, then usually the best power to brightness ratio can be found with an eyepiece from 5 to 10mm. But as I said, this also depends on the kind of object. Small but very bright objects, such as planets or planetary nebulae, easily accept much higher powers, whereas very dim and large objects need much lower. 

Thursday, 20 April 2017

A weird sombrero

Because of its odd shape, M104 (aka the Sombrero Galaxy) has puzzled the minds of scientists for decades. It exhibits a small, very bright core that is home to a supermassive black hole. A spectacular, dark dust lane encircles the galaxy and is already visible in a pair of binoculars. This enormous ring of dust and matter generates most of the galaxy's stellar formation as can be deduced from the many ripples and structures within it. In between, however, there seems to be some sort of void. 

Recent study revealed that this galaxy in fact consists of two galaxies into one. It's still unclear how this came to be but most probably the Sombrero Galaxy's the result of a collision of two more or less equally-sized galaxies. The heart of the Sombrero remained an old, elliptical galaxy. Remember what I told you about the coffe and milk? When you add milk to coffee and stir it, a spiral structure appears and in terms of a galaxy this means that there's a lot of activity going on. But after a while the coffee and milk have mixed completely and the whole becomes a plain, brownish liquid. The galaxy's energy diminishes, the spiral arms disappear and all that's left is a vast cloud of stars: an elliptical galaxy. The cloud of old stars is very well visible here on the sketch. The second galaxy on the other hand was smeared out by centrifugal forces and formed this ring-like structure, just like the famous rings around Saturn. Therefore you get this old galaxy with little star formation activity in the middle and a ring of young, active material around it. 

This galaxy also seems to possess thousands of globular clusters, hovering around the nucleus. These were invisible to me off course, because we're talking about a distance of 28 million lightyears here. Still in our backyard in astronomical terms but imagine the time it took for its light to arrive! 

 


Saturday, 15 April 2017

A train wreck reborn

The Universe is filled with disaster. All stars will eventually die and some of them will even explode, blowing the planets that orbit them to smithereens. Entire galaxies are withering away because they're lacking the strength to revive star formation. Others are crashing into each other or absorbing smaller companions until they're utterly consumed. Even our seemingly infinite Universe is not eternal and most physicists currently agree that its expansion's accelerating and that it will continue to do so. All matter will eventually be dispersed so much that stars can no longer be formed and the existing stars will all die. Even black holes will disappear in the end since they emit mass through radiation (the so-called Hawking-radiation). The Universe will have no more energy and reach absolute zero temperature. A universal big freeze as it were.

But often these biblical calamities are not the end. NGC4449's a reasonably close dwarf galaxy (well... only 12 million lightyears away), similar in size to the Large Magellanic Cloud that's accompanying our Milky Way and which is a spectacular sight in our southern hemisphere. It can be found near the Cocoon Galaxy and has about the same apparent brightness, so accessible to all under a sufficiently dark sky. Just like the Cocoon, this little bugger's being influenced severely by its close neighbours, in this case an even smaller galaxy and a big globular cluster, both of which were invisible to me. They're perturbing NGC4449 with great force and deforming its entire structure. Let's face it, tidal forces have transformed it into a train wreck. But as you, my loyal readers, know very well, this calamity's actually reviving the Train Wreck Galaxy. I could clearly see many bright knots in it, regions of extreme star formation, much more than e.g. in the Cocoon. Thousands of new stars mean tens of thousands of new planets and probably a lot of new life to go with them. 

So let's enjoy this rebirth before the Univserse will eventually fade away. Well, we probably still have about a hundred trillion years before that happens. 

Thursday, 13 April 2017

Sometimes they do fall apart

Globular clusters... the eternal companions of galaxies, so old that they've witnessed the birth of the galaxy they're bound to. They can contain hundreds of thousands of stars in a spherical area with a diameter usually less than 30 lightyears. Or in other words, the stellar density's hundreds to even a thousand times greater than in our part of the galaxy. If you'd stare at the sky in a globular cluster, it would be filled with stars brighter than our own Moon!

Such a place would be most unfavourable for life because the tidal forces that all these close-by stars generate would disturb any planetary orbit too much, let alone the fierce radiation that they'd cause. A strange quality of globulars is that their stars, in spite of being among the oldest stars in the universe, often appear very blue and hot. Usually old stars tend to cool down and become orangy-red. The reason for this is that in a globular cluster the stars are so close to one another that they're able to strip each other's atmosphere, exposing the extremely hot core. Now imagine what they could do to a miserable planet's atmosphere!

Due to their huge density globular clusters are able to resist the galaxy's gravitational pull because stars within a few hundreds of lightyears' distance are influenced more by the gravity of the globular cluster than by the galaxy. Therefore they remain very compact and will continue to do so.  

But there are always exceptions.

Next time you're planning to observe the imposing globular M3, half-way between Bootes and Canes Venatici, point your telescope slightly more towards the northeast. There you'll find this much less known globular, called NGC5466. You'll immediately notice that it's not perfectly spherical like most of its peers, but highly irregular in shape. Stars seem to be scattered all over the place and the thing that struck me was that the stars appeared to form chains in more or less the same direction. After having done some research, my observation turned out to be correct. This particular globular cluster's losing the battle against our Milky Way and is being ripped to pieces as we speak! Its stars are being spread into a large stream between Bootes and the Big Dipper (invisible to amateur telescopes because too faint and distant), just like if you'd be smearing out a blob of paint with a brush. In a few hundreds of thousands of years this globular cluster will be no more...

 

Monday, 10 April 2017

The great whirlpool

Whirlpools have fascinated writers, artists and scientists since antiquity. I can still remember sitting on the edge of my chair of pure excitement when I was reading how Odysseus confronted the dreadful Charybdis and only just managed to navigate his ships passed it. Now, thirty-five years later, the story still enthrals me and it passes my mind every time I point my telescope slightly south of Alkaid, the outermost star of the big dipper. There you'll find the spectacle that you can see on this sketch. 

M51, or the "Whirlpool Galaxy", are in fact two interacting galaxies as you could've guessed. The little companion, otherwise referred to as NGC5195, came from behind M51 and literally passed through its disk some 500 million years ago. After that it made another disk crossing as recently as 50 to 100 million years ago and currently it lies slightly behind its big sister. Loyal readers of my blog will already have concluded that these events have led to intense bursts of star formation, due to the violent stirring up of matter in both galaxies, and that's exactly what we see here. Look at all these bright knots and patches in the Whirlpool's spiral arms! Those are all vehement star nurseries like the Orion Nebula, but much bigger still. The spiral arms themselves have also been deformed by the close encounter with the dwarf galaxy and aren't perfectly circular. Furthermore I was able to note some very faint nebulosity around the little one and on the right of the main galaxy where the outer spiral arm was clearly torn to pieces... all stars and matter that have been extracted from both galaxies under the unimaginably strong tidal forces of the two fly-throughs.

As spectacular as it may look on my sketch, please don't get too carried away because this is a fairly difficult object. Under a light-polluted Flemish sky, even with my former 18" telescope, I could only make out the two nuclei and some faint nebulosity around them. Then again, under a nearly perfect sky the main galaxy's full disk appeared as a large, cotton patch in my former-former 8" scope. So it's an object that, apart from aperture, also requires a very good sky to be appreciated fully. I'm afraid that I've slightly overdone the overall brightness of the object, having made the digital image nearly two weeks after the original observation and pencil sketch. Difficult to tell; sketching's not exact science, but I hope that you enjoy it anyway...

 

Friday, 7 April 2017

A cloud of invisible stars

Number 48 on Messier's list is an easy object. It's a very bright and large star cluster that's appreciated best in binoculars or a small telescope. Larger instruments will magnify too much and as such peer "through" the cluster rather than fill the field of view with it. But there's no need to despair! Just point your scope slightly to the right, towards the outer edge of the dim but noteworthy constellation of Monoceros, the unicorn. There you'll find this cluster which scientists refer to as NGC2506. It's significantly dimmer and it appears much smaller than M48 - being over 11.000 lightyears away (!) - but it's certainly much more interesting as well. 

For starters, NGC2506's much richer than its apparent neighbour. M48 counts about 80 stars whereas there are several hundred members that belong to NGC2506. The latter's much older too, at least 1,1 billion years against 300 million for M48. You can tell because unlike most clusters which merely consist of young and hot blue stars, I identified quite a few old orangy ones among the blue-white majority. This is quite surprising because, as I told you before, most star clusters fall apart after a couple of hundred thousand years under the gravitational pull of our galaxy. Similar to the even much older M67, this distant cluster seems to resist the tide quite well. That being said, my observation gave me the feeling that NGC2506's slowly giving in and will not hold out as long as M67. I noticed an overall flattened ring sort of shape which may indicate that the stars are being pulled away from the cluster's core, ready to be hurled into empty space. 

Being so incredibly distant also means that this cluster's difficult to resolve into individual stars. Modest telescopes will only show a nebulous patch with a couple of little stars in front and even with my big binoscope I wasn't able to distinguish every single star. Many remained hidden in the faint cloud. Nonetheless this is a beautiful and challenging object that I simply had to share with you.

Monday, 3 April 2017

Cocooning

With the word cocooning we usually express a sensation of protection in the sanctity of your house or favourite place. A feeling of leisure and not having a care in the world. Ah... what a comforting thought that is...

So how on Earth did anyone attribute the nick "cocoon" to this pair of galaxies that are currently racing past one another? Possibly because the biggest one does resemble and insect's cocoon at lower magnifications, but that's as far as my imagination goes. NGC4490 (the big one) and NGC4485 are a pair of closely interacting galaxies. The little one's just passed the closest point of its incredibly fast fly-by which has left the bigger one significantly distorted. Well... "just passed"... we're talking about millions of years ago here but in astronomical terms that's "only just" of course.

It's not the first time that I've written about galaxies that are zooming past or even crashing into each other (see e.g. my video about a galactic tango here). This universe is incredibly big but gravity, being only the third or the four forces that govern it, still remains absolute. Also the Andromeda Galaxy will crash into our Milky Way in 5 billion years' time. But as I've explained, that doesn't need to mean doom. On the contrary, these close encounters stir the matter in those galaxies up, triggering a burst of new star formation. Look at NGC4490 and the many bright regions that I managed to distinguish. These are areas of new, very intense star formation and so the fly-by of little NGC4485 has brought uncountable new stars into existence and... probably... a lot of new life with them. 

What a cocooning thought... :-)

Sunday, 2 April 2017

Jupiter and the effect of "seeing"

Street lights and bad weather are not the only enemies we astronomists have to contend with. There's also a sneaky adversary up there which will only reveal itself when you're looking through a telescope: our atmosphere. Twinkling stars may appear romantic, to us this is usually the sign that the observing night we were looking forward to so much will probably turn out to be very disappointing. Air turbulences, or "seeing" as we like to call them, are caused by the movement of the air mass around and above us, especially when there's high wind or a powerful jet stream around. As invisible as these turbulences may be to the naked eye, when your telescope magnifies 100x it also magnifies the ripples in the air just as much. Especially when you're trying to observe subtle details on a planet or when you're trying to separate an exceptionally close double star, these turbulences will mess up your view up to the point that you'll soon give up and go to bed.

In order to give you an idea how difficult planetary and high-resolution observation is, I've created this small simulation to show you how I really observed Jupiter the other night. Now you'll understand why the Hubble space telescope's so important.

 

Friday, 31 March 2017

Jupiter

I know that astrologists believe that Jupiter's in Libra right now but, sorry guys, it's actually right above Spica, Virgo's most prominent star. You should look up to the sky a bit more often... :-)

Jupiter's the biggest planet of our solar system, only preceded in brightness by Venus from Earth's point of view, if you don't count the Sun and the Moon. Its mass is two and a half times that of all the other planets combined and over 1.300 Earths could fit in it. Jupiter's gravitational pull's so strong that it manages to make the Sun wobble! In fact, you could describe this giant planet as a failed star because it emits more energy than it receives. And yet, our Sun, the tiny star that it is, still dwarves it. 

Jupiter's not a rocky planet like Earth but it's a big ball of gas. In case you'd like to visit it, be prepared for a storm because on Jupiter the wind velocity exceeds 600km/h, that's TWICE the wind speed of a tornado! These incredible winds create the well-known creamy and brown stripes that you can already see through a small telescope. Another famous feature is of course the great red spot that appeared very orangy in my binoscope. This is a gigantic hurricane that could easily contain three Earths! Imagine that! 

Jupiter has no less than 67 known moons, the four biggest of which had already been identified by Galilei, hence "Galilean moons". The biggest's called Ganymede and you can see it as the second moon from the planet on my sketch. Ganymede's also the biggest moon in our entire solar system and overthrows even Mercury in size. Closer to the planet we find Io, a moon that's distorted so much by Jupiter's powerful tidal forces that its surface's mashed into one big, constant volcano. On the edge of the field of view you can just see Europa, a very unusual moon that hides a water ocean under it's icy crust. Analysis of the brownish substance we can see on its surface suggests that this ocean may contain very complex molecules, if not foster life itself. Callisto, the fourth of the bright moons, is also the most distant one and as such didn't appear in this highly magnified field of view.  

April's the ideal month to observe Jupiter since it will be closest to Earth. So grab your binoculars or telescopes and enjoy the ever-changing spectacle that this fast-rotating planet has on offer. 


Wednesday, 29 March 2017

The Intergalactic Wanderer

Globular clusters are among the most spectacular objects out there. Imagine these almost perfect spheres that consist of hundreds of thousands of stars! They usually accompany a parent galaxy, although the word parent is somewhat out of place because globular clusters are generally older than the galaxy around which they orbit. They're among the oldest objects in our universe and contain the oldest known stars. Life in such a place would be hard to find since any possible planet would experience severe tidal disturbances from the multitude of extremely close stars.

As I said, globulars are usually bound to a galaxy and have the same origin. But every now and then there's this oddball (literally in this case) that doesn't exactly follow the rules. NGC2419 not only lies almost exactly opposite to our galactic centre, it's also such a distant globular cluster, travelling at some 300.000 lightyears away from us, that scientists believed for a long time that it was a loner and not tied to our galaxy at all. Hence the nickname "Intergalactic Wanderer". Recent study changed that view somewhat and we now know that it does obey our Milky Way's gravitational pull, albeit with some reluctance, and that it makes one rotation every 3 billion years. That's a very long time, isn't it? 

From an observation point of view, it's a rather faint globular obviously because of its extreme distance, but it should be visible also in modest telescopes given a not too light-polluted sky. resolving stars in it is another question. Whereas most other globulars will happily resolve into an uncountable amount of individual stars, you'll have a run for your money with this one. A friend of mine stated that he's never been able to resolve it with his 24" telescope, not even at 400x. With my binoscope I did manage to see some individual stars at 504x, but for the rest it remained a grayish blob with some hints of structure. Yet, the peculiarity of this object does make it a worthwhile winter target. 

   

Tuesday, 21 March 2017

Hubble's variable nebula

Ask ten astronomers about their favourite winter objects and maybe only one of them will mention NGC2261. This is really astonishing because this little nebula's quite bright, peculiar in shape and offers some remarkable detail at high magnifications. Yet, it roams in the shadows of much more famous objects such as the Orion, Rosette or Horsehead nebulae. It never ceases to amaze me that many astronomers prefer to peer for hours trying to spot the almost invisible Cone Nebula rather than having a look at its small but o so beautiful neighbour. And a real neighbour it is because NGC2261's an outlying part of the large Cone Nebula complex, which lies 2.500 lightyears away from us. In turn, this nebula complex is but a part of the gigantic Orion molecular cloud.

When Sir William Herschel discovered NGC2261 in 1783, he mistook the nebula for a comet and I'm sure that you can see why. The bright tip envelops the young double star R Monocerotis, which is thought to be only 300.000 years old. The system's surrounded by a thick disk of gas and debris, much like the one in which the planets of our solar system were born 4.5 billion years ago. As some of this debris falls into the stars, much of it gets ejected again. The dust around the stars' equators blocks this outflow, but at the poles the way out's mostly clear. The result is that gas and dust blows out in two opposed jets and one of these happens to be directed at the bright nebula. Just like the smoke from an oversized industrial chimney, the expelled matter forms dense clouds that drift in front of the nebula and sometimes block some of its light. In 1916 Edwin Hubble noted that the nebula changes brightness quite rapidly indeed, up to two full magnitudes in a matter of months. Comparing recent photographs to older ones shows that the nebula's also changed shape considerably over time and will continue to do so at a very fast rate until the newly formed stars stabilise and enter their adult life. Then the nebula will gradually expand and dissipate until it will have disappeared completely. 

Thursday, 16 March 2017

A pear-shaped cluster

I hope that it's just this star cluster being pear-shaped and not my observation... :-) The reason why I say this is because M67, a bright star cluster in the constellation of Cancer, is extremely old. Estimates vary between 3,5 and 5 billion years and this is extraordinary. As you remember, most star clusters are soon ripped apart by the gravitational pull of our Milky Way and the individual stars each go their own way some hundreds of thousands of years after they're born. But M67 seems to resist till the bitter end. Most of its stars are therefore middle-aged and in many ways comparable to our own Sun. Actually, it was once thought that our Sun also originated from this cluster, but that seems very unlikely now. You may also notice some reddish stars, which are the most massive ones in the group. Because of their great mass they've already run out of hydrogen and have swollen to red giants. Yet, I've also observed several young, blue stars in it, hence why I was having doubts about my observation. But a quick check revealed that quite a few young stragglers have been absorbed by the cluster. The more new stars the cluster absorbs, the greater its overall mass becomes and the more it manages to resist the gravitational pull of our galactic centre. Over 500 cluster members have been classified so M67's one of the largest clusters in our vicinity... well... it's only 2.600 lightyears away. It's total mass is estimated at 1.400 solar masses and originally it could have been even ten times greater! Imagine the gas cloud needed to produce 5.000 stars... it would have dwarfed the Orion Nebula!

Because of its proximity and the great variety of stars it contains due to its age, M67 has been observed extensively for the study of stellar evolution. Having such a strange cluster so close that you can already observe it quite easily with ordinary binoculars is much more convenient of course than having to peer at some of the other very old clusters like NGC2158 or worse... Be19, which are extremely far away.  

Tuesday, 14 March 2017

Just another planetary... or not?

As I explained already several times, planetary nebulae are formed when an old star becomes unstable and dies. The fusion process comes to a halt, making the core collapse whereas the outer layers of the star are expelled and form a gaseous bubble. Hence the name "planetary" because these nebulae are usually small and round and therefore somewhat resemble a planet.

The one I'm presenting to you now's denominated IC2165 and can be found in the constellation of Canis Major, the great dog, almost half-way between bright Sirius and Orion's left knee. It appears very small because it's quite distant, being more than 6.000 lightyears away from us, but as with most planetaries it's still quite bright and supports high magnifications well. Yet it was difficult for me to make out any detail in it, although I did see a brighter, elongated inner shell. This inner shell's caused by the collapse of the central star whereas the fainter, large bubble consists of gas that had already been expelled earlier, during the star's last, unstable phase. The inner shell obviously travels a lot faster than the outer, being propelled by the sudden collapse of the star, and is quickly nearing the outer shell where both will merge and eventually dissipate into space together under the strong stellar wind from the collapse. Scientists believe that this nebula has entered a late-intermediate phase due to the proximity of the inner shell to the outer and the much faded central star, which was indeed invisible to me.  

Friday, 10 March 2017

An exploded jellyfish

Actually, the title of this blog post's a bit misleading because in reality the explosion caused the jellyfish and not the other way around, but I thought it sounded nicer this way. Now what on Earth is going on here? The nebulous filaments you see on this sketch are the remnants of a supernova explosion, quite similar to the ones that caused the Crab and the Veil nebulas. The Jellyfish Nebula (or IC443 if you like) decorates the winter constellation of Gemini and contrary to its two more famous counterparts it's a lot more difficult to observe. For starters, it lies much further away from us - some 5.000 lightyears compared to 1.470 for the Veil - and it's probably much older and therefore more dissolved into space. Given its large size and considerable distance we find that the Jellyfish extends 70 lightyears across, much more than the Veil's 50 lightyears. But this doesn't mean that the Jellyfish isn't an interesting object at all; much on the contrary I would say. Yes, it does take a reasonable amount of telescope and a dark sky to spot it, but as you can see on my sketch it does have a quality that is no second to many of the brighter nebulae in the sky. If you get the chance to observe it through a really big telescope under a really dark sky the delicate whisps and filaments reveal themselves just in the same way as they do in the Veil. All that you see is gas and other matter that's blown away by the incredible shockwave that the supernova explosion generated. Remember that a supernova releases more energy in a fraction of a second as our Sun produces in its entire life! The initial velocities of such a shockwave can be as high as 30.000km/s, or one tenth on the speed of light, and the resulting gas bubble's heated up to millions of °C! Of course, our Jellyfish has slowed down (30km/s) and also cooled down (10.000°C) considerably over time and probably within the next centuries its expansion speed may fall below the local speed of sound. Unfortunately there's still great uncertainty about the age of this nebula with estimates varying between 3.000 and 30.000 years. Recent observations with NASA's sophisticated X-ray telescope, however, seem to confirm the latter figure. 

The Jellyfish is also an interesting object from another perspective. It lies within a dense molecular cloud complex and therefore scientists have studies this nebula to a great extent in order to see how the expanding blastwave interacts with the surrounding gas clouds. It's also been suggested that the star that caused the Jellyfish explosion had such a short life - perhaps as short as 30 million years - that it was still enveloped by its original birth nebula when the supernova went off. All that's left of it now is a tiny neutron star, merely 10km across but with a mass that's perhaps twice as much as our Sun's. Imagine how heavy it must be and how great the force must have been that was able to compress all of that matter into such a tiny ball! It's spinning rapidly whilst emitting radiation in a beam, much like a lighthouse on speed. Such pulsating neutron stars (or pulsars) can turn at a speed of several hundred rotations per second and they do this with such an accuracy that make them the most precise clocks in the universe.

Wednesday, 8 March 2017

The baby boom galaxy

In my previous post I told you about the close encounter of the M81 and M82 galaxies which happened a few hundred million years ago. As you could see on the sketch, M81 remained fairly intact after the M82 fly-by. Now have a look at the latter. Although evidence of a spiral structure has been found recently, it's obvious that this small galaxy has been deformed dramatically by the tidal forces that the encounter generated. Gas and dust have been stirred up severely and the main dark structures can already be observed through a small telescope. 

Now, what would be the consequence of all this, you might ask? Is this galaxy headed for destruction? Will it blow up? Fall apart?... Nothing of the kind! Actually, this galaxy's become a baby boomer! In another post I explained that galaxies are a bit like a cup of coffee. Older galaxies are like a cup in which the milk has been mixed completely. It's cooling down and the coffee has a plain, unattractive light-brown colour. Not much activity going on in that. Young and active galaxies, such as our own, are like coffee to which the milk's only just been added and which you're giving a good stir. The white trails of milk form a spiral pattern in the coffee and there's a lot of activity going on... clouds of gas and matter that are swirling, contracting and... forming stars. Now consider this little bugger. Here the milk's not simply been added and stirred. Oh no! In this case a whole can of milk was poured in at once and the coffee and milk are splashing everywhere! How about that for activity! The Hubble space telescope's discovered 197 starburst clusters in the core of this galaxy with an average mass of 200.000 Suns. This means that every single one of them is like a supermassive globular cluster of stars, all within the galaxy's central region! Stars in the core of this galaxy are being born ten times faster than they are in our entire Milky Way and consequently there are also much more supernova explosions when the biggest of those stars reach the end of their very short lives. Exactly three years ago one of these supernovae happened and could even be observed through ordinary binoculars. Here you can see the sketch that I made at the time with my former 18" telescope. The high supernova rate (about one every ten years) generates incredible superwinds that blow out matter from the galaxy's core as you can clearly see on my sketch. Most of this matter will eventually fall back into the galaxy (remember the splashing coffee) or form small and active satellite galaxies such as UGC5336 near M81.   

The universe never ceases to amaze us...

 

Monday, 6 March 2017

A perfect spiral

M81, or the 81st object on Charles Messier's list, is the brightest member of one of the nearest galaxy clusters to our own. Actually this cluster's much larger than ours and contains no less than 34 members, although the larger part of those are dwarf galaxies that are beyond the reach of most amateur telescopes. A few others, however, are a real treat such as strange M82 which lies almost as close to M81 as measures the diameter of our Milky Way (I'll tell you more about M82 in my next post). On the other side of the cluster lies NGC4236, of which I told you here recently, at a distance of 12° in our sky or almost 4 million lightyears from M81. All of these galaxies are physically interacting with each other and especially M81 and M82 (and less known NGC3077) have a very strong bond. A few hundred million years ago a close encounter took place between M81 and M82 during which the latter was dramatically deformed. M81 on the other hand survived this encounter almost intact but still the enormous tidal forces generated a lot of star forming activity in it. It is difficult to see the many star forming regions with amateur telescopes but you might notice the brighter knots in the spiral arm just below the two little stars below the nucleus. The interaction with M82 has also sucked out a lot of matter from both galaxies which led to the formation of filamentary structures in between them. Some of these gas glouds have fallen back into M81, leading to even more starburst activity.

For those of you with a keen eye, you might notice a faint patch towards the left-hand border of my sketch. This is an irregular dwarf galaxy denominated UGC5336 (or Holmberg IX) which is a close companion to M81. It's very young, with an estimated age of merely 200 million years and therefore scientists believe that it may have formed out of the debris left from the M82 fly-by. 

The M81 galaxy cluster's estimated to be 12 million lightyears away from us.

 

Sunday, 5 March 2017

Decorated with a rosette

The night's sky is the most bewildering spectacle that we, insignificant human beings, may behold. That is, if you go to one of the few areas left on our planet that aren't contaminated by useless street lights that we in our stupidity believe to make our lives safer. But if you're lucky enough to dwell in one of these rare places of exceptional darkness and the weather gods play in your favour too, try to look up a little more and you'll understand why we astronomers live our hobby with such great passion. While you're at it, try to ignore the imposing constellation of Orion which carries the famous nebula in its sword. Instead, look a bit to the left, to the almost indistinguishable constellation of Monoceros, the unicorn. Even though it doesn't contain any bright stars, the Milky Way decorates it with one of its brighter knots which means that you're bound to find lots of treasure in it. The most famous treasure is without question the glorious Rosette Nebula, which is so amazingly complex that it has no less than four scientific denominators: NGC2237-2238-2239-2246, plus another one for the bright and young star cluster within it (NGC2244). 

It is visible to the naked eye, but as I suggested you need a really dark sky for it. The Rosette is yet another area of massive star formation in our galaxy and with its radius of 20 lightyears it's also one of the biggest, even twice as big as the great Orion Nebula! The reason why it's so much fainter is because it lies 5.000 lightyears away, or almost four times further than its more famous counterpart. The Rosette proves to be a challenging object exactly because of its size. The frail light that eventually reaches us from it, is smeared out over a surface that would fit four full Moons! Luckily a binoscope offers the advantage that you can keep magnification lower for the same light gathering power so I managed to capture most of the nebula in the same field of view and with remarkable brightness. Look how the stunning Rosette's swirling around the newborn stars that are its offspring! Look at all those filaments of gas and dark matter that are yet contracting to form even hundreds of other new stars! Isn't it about time that we all turn the bl**dy lights off and start admiring what lies out there again, as did all of our forebeareres, instead of living in this tiny little world of fashion and social media?

 

Tuesday, 28 February 2017

On the border of intergalactic space

Yes, I know... Here I am again with a sketch on which you can't see a bl**dy thing unless in total darkness and after staring at the computer screen for three hours with averted vision. But Berkeley 19 (Be 19) is a very interesting open cluster, meaning that it's extremely old (perhaps even older than our galaxy itself) and that it lies at a distance of 25.000 lightyears. In other words... this cluster lies BEYOND the outer arm of our galaxy! If you go any further, you'll find yourself in the absolute void of intergalactic space! 

To give you an idea what it would be like to live there... Imagine a world where half of the year the only thing you see is the Milky Way splitting the sky in two, with perhaps here and there some stray stars, and the other half the sky looks completely empty and black to the naked eye. If you're lucky, you might spot a few faint, hazy patches of nearby galaxies such as Andromeda or M33, but that's it. For the rest the sky would appear as total emptiness. Well, it would have its compensations because for sure the astrologists would be out of business. :-)

But let's return to Earth. When I found out about this distant cluster I was immediately fascinated by it because of its extreme location. I had already tried a few times to spot it but since my telescope's database doesn't know it, I had to look for it visually (without a finderscope) and it turned out to be more difficult than I had imagined, even though it lies at only a small step from bright star Elnath. When I had eventually found the right place according to the map and with a magnification of 104x... I didn't see anything. Neither at 190x. At 285x I thought to have seen something (maybe) and only at 504x I've seen some of the cluster's stars. Centrally I noted a sort of a pentagon and there were two detached lobes, one above and one below. 

I could of course render extremely difficult objects like these a bit brighter on the sketch, making them more easily visible for you. But that wouldn't be right in my opinion because it might give you the impression that it was just as (clearly) visible through my telescope, whereas it wasn't. Sketchers like me thread on a very difficult line between realism and artistic expression. Sometimes I've not rendered an object bright enough, sometimes I've overdone it a bit. It's so difficult to tell how bright an object really was at the eyepiece, especially since I'm doing the processing on the pc sometimes days after the observation itself. In the end I try my best to give you the same experience as I had. Perhaps it's also more rewarding for you this way... 

"I've seen it!!!" :-)   

Friday, 24 February 2017

Near but so easily overlooked

Some astronomical objects receive far less attention than they rightfully deserve. There may be many reasons for this, as for example that the object in question's too challenging. But that's a real pity because sometimes even the more difficult objects can turn out to be extremely rewarding. 

NGC4236 is a galaxy that resides in the tail of Draco, the dragon. It's a member of the M81-M82 group and therefore it lies only 11,7 million lightyears away from us. In astronomical terms, that's our backyard. Actually, NGC4236's only slightly smaller than our Milky Way and therefore it's by far the largest group member, significantly bigger than it's two famous neighbours. We also see this galaxy under a shallow angle, meaning that its light isn't dispersed over such a large area as is the case with galaxies we see face-on, like M33 for example. In short, NGC4236 has all that it takes to become one of the most popular astronomical objects. And yet, it isn't as it's surprisingly dim and contrary to smaller M81 and M82 it's unsuitable for small telescopes. The reason for this is unknown to me... I suspect that much of its light must be absorbed by a cloud of interstellar dust. Strangely enough NGC4236's located well above our galactic plane so its light doesn't have to plough through a lot of Milky Way matter, but it's the only explanation I can think of. All I can say is that it's a real pity because NGC4236 has so much to offer if you take the time for it. 

As I expected, this galaxy didn't "leap out" of the eyepiece at all when I turned my binoscope at it. The central bar was easily visible, but not more than that. Quite disappointing, but I didn't give up so easily. I tried to focus, used a bit of averted vision and let my eyes adjust fully to the telescope view. Little by little... I started to see more. The central bar wasn't homogeneous at all, but showed some interesting brighter knots. Eventually also most of the faint spiral structures slowly revealed themselves to me. What a beauty it was! A perfect barred-spiral galaxy under a perfect viewing angle... 

So please, next time that you're out and the sky's dark enough, give this one a try. I'm sure that you won't be disappointed!


But... wait a minute! I'm not finished yet! I didn't know this at the time of observation and discovered it only when I was doing some research for this blog post. But look on the right-hand side of the bright central bar. You'll notice that above the end of this bar there are two small, brighter patches. The middle one of which is... another galaxy!!! Yes! It's a dwarf galaxy that accompanies its big sister, just like M32 and M110 accompany Andromeda. But in this case PGC39369 lies right in front of the main galaxy and this makes it a thousand times harder to see. But it's there!!! I saw it, even without knowing it existed! 

How about that for a satisfactory emotion? Oh well... I know, I'm just a geek... :-)



Monday, 20 February 2017

The helmet of mighty Thor

I've already written about this spectacular nebula in Canis Major here, but it's so beautiful that I couldn't resist dedicating a second blog post to it. NGC2359 or "Thor's Helmet" is another astronomical showpiece that leaves anyone who has the chance of seeing it through a big telescope in awe. As I explained, the cause of this incredibly complex nebula is the star at its centre. It's one of those rare Wolf-Rayet stars, just like the one in the Crescent Nebula. They contain at least twenty times the mass of our Sun and burn their hydrogen much faster. Once they've run out of sufficient fuel to keep the fusion process stable, they start fusing helium into heavier elements such as carbon, nitrogen and oxygen. The consequence is that the star's blown up to gigantic proportions, so big that even Jupiter might be swallowed by it if that star were at the centre of our solar system! The star's surface cools down and turns orangy-red. A famous example of a supermassive star in this phase is Betelgeuse, Orion's left shoulder (from our perspective). The star becomes highly unstable, gravity fighting with the outward energy generated by the nuclear fusion in its core. It expands, cools down, contracts, heats up and expands again... until the critical limit's breached and the star's outer layers are expelled into space. But contrary to normally sized stars, these supergiants will not simply let their atmospheres dissipate into a planetary nebula while their cores slowly extinguish as a white dwarf. Oh no! They're simply too big for that!

By shedding a part of their atmosphere, a supergiant can regain a certain amount of stability. It contracts so much that its surface reaches a temperature of 200.000°C or more and fusion's re-ignited, only this time carbon and oxygen are being fused into heavier elements still, like iron for example. Imagine the power behind all this! Imagine the fierce stellar winds that such an extremely hot star generates! The previously expelled bubble of atmosphere's blown up into space at incredible speed, like a balloon. That's exactly what we can see here at the nebula's centre. 

Soon the central star will collapse under its own gravity and explode as a supernova, which will feed the universe with heavy molecules that are vital for the creation of planets and life.

For the record, the previous sketch of Thor's Helmet was made with my old home-built 18" Dobsonian, whereas this was observed through my 18" binoscope. 

Sunday, 12 February 2017

Almost invisible, but that's the challenge

What is it that pushes us astronomers to go hunting those little blobs so faint that you almost need a healthy dose of imagination in order to see them? Why are we so passionate about staring through a small hole for hours in the biting cold until we eventually think that we've seen "something"? The answers's very simple: because it's a challenge! Because we want to be able to raise our heads and say to the world that we've seen it. Or because we want to discover something that no-one has ever discovered before. Of course, in these days of Hubble and high-definition photography there's anything left for us amateurs to discover with our limited telescopes and poor human eyes. But we don't want to give up and stubbornly try to push our observations to the limits. There's barely a challenge in observing the Orion Nebula or a bright star cluster. But there is a challenge in observing... ARO 215 for example. What the heck is ARO 215 (also known as Abell 7) anyway? It's an old planetary nebula in the constellation of Lepus, the hare, that's become so large that it's almost completely dissipated into space. This is an object that's reserved for the largest of telescopes or, better still, a big binoscope because this instrument allows you to observe at lower magnifications for the same light-gathering power. Since ARO 215 is quite large with its 13 arc minutes diameter, you need as low a magnification as you can get in order to observe it. The sketch below represents very well how I saw it with my 18" binoscope. Are you getting the idea of how faint it is? The Medusa was faint, but this... must've been the faintest object I've observed so far! 

Aren't you seeing anything? I advise you to turn off the lights and to have another look. Go on... concentrate, as I had to do behind the telescope. You didn't think that I was going to make things easy, did you? Use averted vision because your eyes are more sensitive to light next to the point where they focus. Now are you seeing something? You may even discover that I saw two distinct lobes in this planetary with the left one marginally brighter than the one on the right. And that... dear readers... is the kick that we astronomy-weirdoes are so addicted to!

Wednesday, 8 February 2017

Nothing to do with it!

Last month I explained how deceiving appearances may be. Things that seem to belong together from our point of view may not be related to one another at all. In this post I'd like to take you on a trip towards one of the most spectacular star clusters in our sky: M46. One of the peculiar things about this star cluster is that it seems to lie right next to another and even brighter star cluster: M47. They're so close that you can easily catch them together in the same field of view with a pair of binoculars:


M46, the richer but fainter star cluster lies on the left, whereas you can see the younger and brighter M47 on the right. They look like a couple don't they? With a bit of fantasy you could even swear that M47's spitting stars in M46's direction. But don't be fooled! M47's not only brighter because it contains younger and hotter stars, but most of all because it lies thousands of lightyears closer to us. It lies at a distance of 1.600 lightyears whereas M46's 5.400 lightyears away.

Now concentrate on far-away M46. Towards its top edge you might see a little patch. It's extremely difficult to make out, but if you focus well enough (and perhaps turn off the lights) you may spot it. Now let's take my old home-built 18" telescope and zoom in at 85x:


On this sketch which I've made 4 years ago you can see the little "patch" on the right-hand side of the cluster's centre. Keen readers of my blog will already have guessed what it is: a planetary nebula! Yes, this is an enormous shell of gas that was blown away by a dying star. You can already see a lovely doughnut shape in it, can't you? Indeed, in every aspect this little planetary nebula resembles the famous Ring Nebula a lot. Now let's take my new binoscope and zoom into it at 504x:

 

Here you can see our little planetary, called NGC2438, in all its glory. Also its central star's quite obvious. Much more so than with the Ring Nebula you can see that the gas cloud's not really a ring but more a sort of a cylinder, or something halfway a cylinder and the apple without core like the Owl Nebula. See how it's surrounded by the cluster's many twinkling stars that seem to say farewell to the dying companion in their midst. 

But... wait a minute... the nebula seems to be travelling at a much higher speed than the stars in the cluster and in a slightly different direction too. Actually, the gravitational force of the cluster wouldn't nearly be strong enough to be able to hold the dying star and its nebula if they're travelling at that speed. What's more, M46's a cluster of young stars that are hardly 300.000 years old. The star that caused the planetary nebula on the other hand must be billions of years old. It simply can't be a member of the cluster! Recent distance measurements revealed that it is in fact more than 2.000 lightyears closer to us. So it has... nothing to do with it.

Tuesday, 7 February 2017

The eyes of the owl

In the constellation of Ursa Major - popularly known as the "big dipper" or "chariot" - resides a fascinating planetary nebula which astronomers refer to as M97. It's one of the faintest objects on Messier's list and being 3,4 arc minutes across it's pretty large for a planetary, meaning that its frail light's dispersed over a large surface. But already with an 8" telescope you'll be able to see why this nebula bears the nickname "Owl Nebula". If you look very carefully, you'll see two big, dark "eyes" in it. 

Actually, these "eyes" are only coincidental due to the angle at which we see this nebula. As I explained in many earlier posts, planetary nebula are caused by dying stars of normal size which become critically unstable and shed their atmosphere into space. The radiation from the extremely hot stellar core that's left over (surface temperatures can easily reach 100.000°C or more!) makes the gas bubble glow and so we can easily observe it. Often this gas bubble takes an hourglass or even cylindrical shape because the star's atmosphere's much thicker around its waist and therefore the gas can escape much easier from the poles. One fine example is the Ring Nebula, which isn't a ring at all but a cylinder we see face-on. In the Owl Nebula's case the nebula's quite spherical but it has two big holes, one on either pole, where gas ejected at much greater speed. An easy way to imagine this nebula is to see it as an apple from which the core's been removed with a corer (top-right to bottom-left). But Owl Nebula sounds much more intriguing than Apple-Without-Core Nebula and it does seem to stare at you, doesn't it? 

It's 8.000 years old, lies 2.000 lightyears away from us and is expanding at 30km per second. In 10.000 years it'll be gone.

Sunday, 5 February 2017

And now for something completely different...

I thought, after the spectacle of the Orion Nebula: "Now let's show you something incredibly difficult". Minkowski 1-18 (M1-18) is a planetary nebula. Being of the 14th magnitude it's also an incredibly faint one and you need quite a bit of telescope and a very good sky in order to see it. I've read about someone who claims to have seen it in a 10" scope but that doesn't sound very credible to me since it was as close to invisible in my 18" binoscope as it could get. The reason for that is that it must be very distant. I couldn't find any details about this little nebula anywhere but considering its location in the southern constellation of Puppis (the stern) and its faintness I assume it must reside somewhere in the furthest extension of the Perseus arm of our Milky Way. This means that we're talking about a distance of some 12.000 to 18.000 lightyears. This also implies that we're still seeing it because light's travelling so "slowly". The light that we're seeing today of this nebula started its voyage some 12.000 to 18.000 years ago. But in reality this nebula's already dissipated into space much more by now, probably beyond the point that it would still be observable visibly through amateur telescopes. It's one of these odd effects when considering the size of the universe and the speed of light. Probably we're seeing many things in out sky that in reality are no longer there, but the light of the events that caused their disappearance hasn't reached us yet. Observing the stars is observing the past and the further you look, the further you're looking back in time. But for now, let's still enjoy little Minkowski 1-18 and the challenge that it takes to find it. In the end, that's also one of the things that makes astronomical observation so rewarding. Often you can spend hours trying to find something. And when you eventually do find it, it fills you with a deep satisfaction and a gratifying sense of achievement. 

So on you go... try to find it on my sketch! :-)

Friday, 3 February 2017

The Orion Nebula in all its splendour

I've already written many times about the Orion Nebula (see e.g. here and here) and I've also created a video about what it would be like to fly through it with a spaceship. The Orion Nebula, or M42, is of course the brightest nebula in the sky and can already be seen quite easily with the naked eye, even under less than perfect conditions. It's a giant stellar nursery, where hundreds of baby stars are born out of the vast, glowing hydrogen clouds.

I wasn't actually planning on making another sketch of it for the moment because it's such an impressive object that it always takes me many hours of work to put it all on paper (or on the pc). But when I had another peek at it last week, I was so shocked by what I saw that I just had to sketch it. It was in fact only the second time that I'd looked at the Orion Nebula with my new binoscope and as you may recall the first time I concentrated on zooming into it at high magnifications. This time I "only" used 104x in order to see it in all of its glory. And what a glory it was! The bluish colour was more than obvious and the view was filled with its delicate filaments. Nothing out of the ordinary when you've got a big telescope and reasonably good sky. The extraordinary thing was the black cloud of dust that covers the brightest region in part. Really... it was pitch-black, or in any case much darker than the background! Usually dark nebula are hardly visible because they disappear against the dark background and can only be spotted if there's something bright behind them that makes them stand out. That's why scientists are having such a hard time to determine how many dark matter there actually is, and hence to calculate if the overall gravity of all the matter in our universe will stop its current expansion or not. But in this case, I observed how the dark dustlanes continued into the background and what's more, I "felt" that they were well in front of the nebula as if I saw them in 3D.

It's theoretically impossible to see objects as distant as stars in 3D, simply because they're too far away and the light rays come from "infinity", meaning that they don't reach our eyes under different angles. There is however a theory that explains why observing with both eyes such as with a binoviewer or binoculars can still give a 3D feeling, and that's because the light's diffracted differently in both eyes. But here I was far beyond a mere superficial feeling of three dimentions. This was like seeing the Orion Nebula through a Viewmaster (those who've grown up in the 70ies or 80ies will know what I'm talking about :-) ). I had the impression that slightly changing the position in front of the eyepieces also made the view change, as if the dark cloud would move a bit to one side or the other! This is of course complete nonsense, theoretically speaking. The whole idea simply must be a distortion of my human brain. Well, I don't care because astronomical observing is all about sensations. This was perhaps the strongest sensation I've had... ever. 

Wednesday, 1 February 2017

Dark Medusa

Medusa; the frightful woman with snakes in stead of hair and a gaze that would turn any ill-fated man that happened to cross her path into stone. She was said to roam the underworld until Perseus, the valiant half-god, would cut off her head whilst using a mirror to avoid her deadly look. People were so abhorred by her name that the Romans eventually called some very nasty creatures after her: jellyfish. 

Now it so happens that there's an exceptionally dark and nasty jellyfish in the winter sky. On the border between the constellations of Gemini and Canis Minor (the small dog), you'll find a nebula so faint that it wasn't discovered until 1955. Scientifically it's called Abell 21, but more popularly it's known as the Medusa Nebula. If you haven't got a big telescope or if your night's sky polluted by the venomous glow of useless street lights, please don't bother. Even with my 2x18" binoscope this nebula wasn't keen on revealing itself at first, although after a couple of minutes some details started to appear to me. The overall jellyfish shape was faint, but fairly obvious and especially the two "tentacles" stood out. 

The Medusa Nebula is a planetary nebula, just like the Ring or Saturn nebulae, albeit a very old one. Many tens or possibly even hundreds of thousands of years ago a star died and shed its atmosphere into space. For a while this huge gas bubble would expand and glow under the fierce radiation from the remaining stellar core. But in Medusa's case, the nebula has now expanded to over 4 lightyears in diameter and the gas is slowly dissolving into space. The central star, or what's left of it, is cooling down and is now emitting much less radiation. Therefore the gas bubble's cooling down as well and hardly emits light anymore. Eventually Medusa will disappear forever.

 

Tuesday, 31 January 2017

A galaxy with a black eye

I've never been very fond of galaxies. Yes, there are some really nice ones such as M51, the famous Whirlpool, or M82, the Cigar Galaxy, without even mentioning Andromeda. But in the end, most galaxies appeared to me as amorphous, faint blobs lacking the details that could make them interesting. Perhaps I should've looked a little better, but in general I loved nebulae a thousand times more. At least these always showed me some remarkable details, frail filaments or internal structures. 

In comes the 18" binoscope and now things have changed. As you can see on my sketches, even very faint and distant galaxies have taken form and character. Sometimes, galaxies now reveal the scars of such cataclisms as we with our small human minds couldn't possibly imagine. I've talked about galaxies being torn apart by another galaxy zooming by such as the Tadpole or the galactic tango of NGC627 and IC1727 (see the video here). I've also already talked about galaxies crashing into other galaxies, such as the Flying Ghost. But in the end, the universe continues to be and even the scariest of scars will heal with time. The Tadpole's long trail of stars and matter will break off and probably form a new mini-galaxy of its own. The two wild tangoers will eventually regroup their stars and in a few billion years no-one will still be able to recognise a flying ghost in the seemingly normal, albeit enlarged NGC520.

And yet, that's not entirely true. Sometimes these scars will not heal completely. Take a small telescope and point it at M64, one of the finest galaxies in spring sky. You will notice that there's a dark patch under the bright nucleus, hence the nickname "Black Eye Galaxy". The larger the telescope, the more prominent this dark patch becomes and with my binoscope I saw it like on the sketch below. It even gave a sort of 3D-sensation to the galaxy's central part as if I was looking at a lunar crater! These enormous dark clouds of dust around the nucleus are caused by a strange phenomenon: the outer 40.000 lightyears of this galaxy are rotating in the opposite direction of the inner 3.000! The friction that this counterrotation causes at the separation point is generating thick clouds of swirling matter and... violent star formation! Now you might wonder... what the heck caused the outer part of a galaxy to counterrotate the inner part? The most likely explanation seems to be that billions of years ago another galaxy collided with it in the opposite direction of its rotation and was eventually absorbed. Perhaps one day the rotation of the large outer region will slow down, come to a halt and will then obey the galaxy's gravitational centre which tells it to rotate in the same direction as the nucleus. But for the time being it's still going its own way and the black eye's the proof that this galaxy's received a pretty hard blow to the head.  

 

Friday, 27 January 2017

Destiny is not an absolute

Yes, I know, this blog post has an awkward title. So what am I talking about here? Look at this older sketch that I made of the bright open cluster M35 in Gemini:


It's a treat, isn't it? Just look at those dozens of twinkling stars that under a really dark sky are already visible to the naked eye. Obviously you've also noticed that faint little blob, just below the drawing's centre. Now let's zoom into that with the binoscope:

 

It's another star cluster, called NGC2158. Is it related to big and bright M35, you might wonder? No, not at all! As I explained in my previous blog post appearances may deceive! M35 lies 2.800 lightyears away from us; to reach NGC2158 you'd have to travel 11.000 lightyears! All right, you might already have guessed that from the first sketch. But there's more! M35 is a typical middle-aged cluster, some 100 million years old, that is now slowly breaking up under the gravitational pull of our galaxy. Soon all of these bright and young stars will go their own way. NGC2158 on the other hand is surprisingly old for an open star cluster, it's age being estimated at 2 billion years! So why hasn't this cluster broken up as well? Isn't the force of gravity an absolute? Yes, of course it is. But first of all, NGC2158's much further away from our galaxy's gravitational centre and therefore it is influenced less by it. What's more, NGC2158's an extremely rich and compact cluster. Even at 285x with my gigantic telescope I wasn't able to resolve all the stars within it. Well, I could have taken the telescope to 500x and then perhaps I would have resolved more stars, but I liked the view as it was. So many stars packed together in such a confined space, means that their mutual gravitational pull outweighs the gravitational pull of our galaxy and therefore they've managed to stay together for such a long time. Many stars in this cluster have already come of age and some have even evolved into red giants, as opposed to the young, blue stars in M35. 

So you see, sometimes an unavoidable destiny can be avoided.

Wednesday, 25 January 2017

Appearances may deceive

When I was observing the remote open cluster NGC1193, I turned my telescope to this nearby couple of galaxies, which listen to the names NGC1160 (on the left) and NGC1161 (on the right). Not that they are that extraordinary to look at. NGC1160 definitely looked fainter than it's bigger sister, although I was able to make out a dark lane near its southwestern border (top left on my sketch). NGC1161 showed a bright and compact nucleus and a faint, regular spiral structure. It's obvious that the latter is the dominant galaxy of the two and its smaller companion looked a bit irregular and even distorted to me, as if it's being cannibalised by the other. 

Now here comes the surprise: they're no couple at all. In fact, they're nowhere near to each other and the brighter galaxy actually lies much further away from us! NGC1160 lies at a distance of 78 million lightyears, whereas big NGC1161's 102 million lightyears away. In other words, the distance between the two's ten times the distance between Earth and the Andromeda galaxy! 

Both galaxies are receding from us at incredible speeds, but nearby NGC1160's surprisingly faster. "Hey! Wait for me!" It's moving away from us at a speed of 2.500km per second (!) whereas big NGC1161 is doing only 1.950km per second. So perhaps... some time the little one may catch up with the bigger one after all. 

Friday, 20 January 2017

Birds leaving the nest

Stars are usually born together. They're brought forth by giant hydrogen clouds that contract under their own gravity into dense spheres; so dense that they light up and start nuclear fusion. The finest example of this in our sky is of course the Orion Nebula, where we can see a whole cluster of stars that's being born right now. The hundreds of young stars are so hot that their radiation causes the gas cloud to ionise and make it emit light as well. Eventually, the gas cloud will be spent. It will cool down and dissipate into space whereas the cluster of young stars will slowly fall apart under the gravitational force of our galaxy and the individual stars will go their own way. The famous Double Cluster in Perseus is a fine example of a group of young stars that has just emerged from a nebula which is now gone. There may still be gas and dust filaments of the Double Cluster's parent cloud flying around, but they're no longer visible to the visual observer and would need long-exposure photographs to reveal. 

But let's fast forward many millions of years. On my sketch you see a lovely little star cluster, scientifically denominated IC1985, which lies some 1.400 lightyears distant. This cluster's a lot older than the Double Cluster or the Pleiades and most of it's stars have already reached adulthood. Strangely enough, in this case we can still see some of the original nebulosity from which the stars were born a billion years ago. I'm speculating now but perhaps the cloud wasn't dense enough to form more stars, yet it was too important to dissipate into space. Indeed, the cluster doesn't appear very rich, does it? So I assume that star formation broke off in an early phase. The nebula has cooled down now, as have the stars in the cluster, and it doesn't emit light anymore. It only reflects the light from the stars within it, or rather, from the stars that're now flying away from it. Yes, this cluster's falling apart and every single one of these stars will become like our own Sun. Planets will already have formed around them and perhaps we could already find the first traces of life there?

There's one oddball on the sketch though, and that's the very bright star somewhat further away. This star's named Atik (or omicron Persei) and it's easily visible to the naked eye, even in light-polluted skies. This star's a blue giant with a mass twenty times our Sun's and it's 80.000 times as bright. Actually it's a complex system of two massive stars that are very close and are evolving around each other so rapidly that both stars have become ellipsoids, rather than spheres. It appears that also this strange couple of giant stars originated from the same cloud as the others, but that it's taking off with greater speed than the rest. Being so large, they will consume their hydrogen much faster and therefore have much shorter lives. Analysis suggests that one of the two has already run out of hydrogen and will soon evolve into a helium-fusing red giant, becoming even hundreds of times bigger.

In the future, the stars of this cluster will lead solitary lives, apart from those that are gravitationally bound such as Atik, but also quite a few other stars as you can see here. They will become double or even multiple stars, which are very common in the universe. Perhaps there are even more double or multiple stars out there than single ones. Also Alpha Centauri, the closest star to our Solar System, is in fact a triple star which... originated from the same cradle as the Sun. Our gas cloud's now long gone, but it's a nice thought that there are still many sister stars of our Sun flying around out there. 

 

Friday, 13 January 2017

Razor sharp

How would our good old Milky Way look if we could see it edge on? Well, pretty much like the galaxy on this sketch. Its scientific denominator's NGC891 and you'll find it a real spectacle, even with modest telescopes. Just look at that impressive dust lane that runs around it like an equator and which seems to cut it in two from our point of view. High resolution images with the Hubble telescope revealed millions of filamentary patterns in these clouds of dust, away from the galactic centre. Scientists theorise that these patterns were caused by several supernova explosions, which blew all the dust and dark matter away.

Apart from its size and luminosity, this galaxy has much more in common with ours. Infrared images and a study of the dynamics of hydrogen in NGC891 have suggested the presence of a small central bar, just like our Milky Way. Imagine that somewhere inside that carbon copy of our galaxy, about halfway between the nucleus and the edge, lies in insignificant little star, around which orbits an even much more insignificant blue planet...

NGC891 is a part of a modest group that contains 7 regular and just as many dwarf galaxies, almost 30 million lightyears away from us.

 

Wednesday, 11 January 2017

Venus in colour

I've never taken a very good look at Venus. Yes, it's the brightest "star" in the sky and perhaps also the most beautiful one. But as soon as you point a telescope at it, you'll be bitterly disappointed. The reason for that is that Venus is covered with a thick layer of clouds, making it impossible to see any detail on its surface. So the only thing you'll see is a white little disk. Well, that's not entirely true because being closer to the Sun than Earth, Venus displays phases, just like our Moon. So if Venus doesn't appear as a disk, you'll see half a disk or a crescent. 

That's what I thought until now.

But my English astronomy friend Paul proved me wrong. Paul's one of the best planetary observers I know and he granted me the privilege to publish one of his sketches here on my blog. On the sketch you see four impressions of Venus. The left one's the normal telescope view and note that these observations were all made during daylight! Paul saw some clear structures in the supposedly monotonous cloud cover, especially that dark patch on the northern hemisphere. 

Next, Paul used three different colour filters. These block all the light apart from a specific colour and sometimes they make it easier to discern specific details on planets. The first is a yellow-green filter (W11) and apparently this made the south polar cap sligthly easier to see. Of course, being the hottest planet of our solar system there's absolutely no ice on Venus, but its polar atmosphere contains swirling vortices of clouds and that's precisely what Paul noted here. The deep red filter (W25A), on the other hand, seemed to kill most of the details on the planet. Finally the blue-violet filter (W47) brought out the dark markings a bit more.

So not only does this sketch demonstrate that Venus deserves a lot more attention from us astronomers, but it also gives you a very good idea of what you can expect when using colour filters.