Thursday 27 April 2017

Jupiter with better seeing

In a previous post I explained that the biggest enemy of astronomers, next to odious public lighting, is the Earth's atmosphere. Last week the turbulences in our atmosphere (what we call "seeing") had settled down somewhat and I was able to make a better observation of the biggest planet of our solar system. 

What struck me at first glace was the large number of dark wisps in Jupiter's bright equatorial belt. They do appear and disappear regularly in the planet's extremely stormy atmosphere but I can't recall to have seen so many of them at the same time. 

Also interesting to note is Io, the third largest and innermost of the Galilean moons, which was transiting in front of the giant planet. Despite being larger than our Moon, in front of Jupiter it looks like a tiny, bright dot. Much more conspicuous was the shadow it cast on the planet and which you can see somewhat to the right. Remember that Io's pulled and squeezed so much by the gravitational interaction with Jupiter and its other moons that its entire surface moves constantly up and down one hundred metres! Compare that to the extremely mild tides on Earth! No wonder that Io displays the greatest volcanic activity of the entire Solar System. 

A bit to the right lies the smallest of the Galilean moons: Europa. As I explained, this is perhaps the most interesting of Jupiter's moons because it hides a deep, liquid water ocean under its icy crust and there's strong evidence that it may even be suitable for life. Of course, Europa's too small and much too far away to be able to discern the many cracks and streaks on its constantly moving surface with amateur telescopes, but I did notice a darker patch near its left-hand border. For this reason I've created a highly magnified inset in the top-right corner, to show you my impression. In reality this moon was just the size of the dot on the main sketch of course. 

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


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.