Tuesday, 18 October 2016

We all have to start somewhere

When rummaging in some old boxes I came across a plastic folder containing my very first astronomical sketches. Back in 1983 I was still a kid but incredibly passionate about the stars, as is obvious from the sketch and the many details I added about the observation. Do you want to know how I made it? You're going to laugh... :-) First, I drew a black disk with india ink for the field of view of my little 60mm refractor with 20mm Kellner eyepiece. By the way, can you believe that I was incredibly proud of that eyepiece at the time? For those of you who don't know anything about telescope eyepieces... suffice to say it equals staring through a small keyhole and these days such an eyepiece would only be used as a doorstop. The object was M13, a globular cluster somewhat bigger than M15, which in my first telescope looked exactly like how I've drawn it: a dull, greyish blob. But... now we come to the real masterpiece: the three stars I chose to portray as well. I painted those with the only bright white substance I could lay my hands on... corrector fluid! Let's say that at times emerging artists have to improvise. :-) 

Browsing through the dozen or so sketches I made this way, brought back fond memories of innocent days and unstoppable dedication to the discovery of astronomy. We should never lose this passion because, although seemingly childish and therefore too often neglected, it will push us to new heights. It's the spirit that drove an extraordinary genius like Bach to write the St. Matthew Passion or Leonardo da Vinci to paint the Mona Lisa. It will also drive you to achieve new goals which you'll be so proud of afterwards, just like I'm proud of my latest sketches, yet convinced that I can do even better next time. I'm not a genius at all. Heck, I'm just an ordinary guy making ordinary sketches that you too can make just as well, as I'm demonstrating with my video series. But nonetheless the satisfaction's equally strong as if you'd created the greatest of all masterpieces.


Friday, 14 October 2016

Beauty lies in the details

Of course, during a public star party everybody wants to see big and spectacular things such as the Moon, the planets, sizzling globular clusters or large and complex nebulae like the one in Orion. If I then show a small but fascinating planetary nebula, such as the Blue Flash, people start to become a bit bored and say: "Nice, but can't you show us something interesting"? This is of course perfectly understandable because most people who've never looked through a telescope don't really know what to look for and, more importantly, how to look. Therefore they fail to see all the tiny detail that you can see on the sketch of the Blue Flash; the lovely, frail filaments of gas which contain the spirit of a star that's just died. If I then turn my telescope to an incredibly distant galaxy such as the one here, NGC6906, they'll simply leave in disappointment and try their luck at someone else's telescope. 

But next time, don't run off so quickly. Take your time. Absorb what's in the field of view. Relax. Let it talk to you. You'd be amazed how much there actually is to see here apart from the "incredibly faint blob" which you see at first glance. First, look at this galaxy's nucleus. It isn't simply round, but has this bar-like structure running through it (click here for explanation). Then look at the spiral arms. There are at least four of them which are clearly visible, two above and two below the nucleus. They're deliciously thin and razor-sharp, don't you agree? Now I'll add some figures. This galaxy's twice as large as our Milky Way and contains 1 trillion stars. Yes!! It's travelling away from us at the incredible speed of 4.800km... per second! That's almost the distance between London and New York... in one second! And finally, it lies 214 million lightyears away from us. 

Of course, loyal readers of this blog have become used to astonishingly vast numbers so there's nothing unusual here, and this is indeed so. There's nothing out of the ordinary about this particular galaxy. Yet, it has its own personality and in spite of the almost imcomprehensible distance it does its best to show us how beautiful it actually is. Therefore, look a bit closer next time you get the chance. I'm sure that you'll be amazed!

Tuesday, 11 October 2016

Suppose that a gigantic star nears the end of its life...

It'll explode as a supernova, right? Yes, it probably (but not necessarily) will. But let's talk about what happens just before the inevitable end. I've already written a lot about planetary nebulae, shells of gas ejected by ordinary stars that run out of hydrogen and become critically unstable. Eventually the remaining, extremely hot core, will cool down as a white dwarf and extinguish while the ever-expanding bubble of gas - the planetary nebula - will dissipate into space. Also our Sun will suffer the same fate. 

Supermassive stars, on the other hand, like to go with a bang. We're talking about stars which are ten to even forty times as massive as our Sun. By the time they run out of hydrogen and become red supergiants, they start fusing nitrogen or heavier elements in their core. They expand so much that they don't have a real surface anymore. Imagine an ocean full of gigantic tidal waves... gas blown up by the unstable core and then pulled back by gravity... One such example is Betelgeuse. This giant star's arrived at a point where it starts shedding its atmosphere into space and at a fast rate too. 

Now let's fast forward many thousands of years. Our giant star's blown vast quantities of gas into space. A planetary nebula on steroids, as it were. These stars, however, are so massive that they're able to regain some stability after having got rid of their outer atmosphere. They contract and become extremely hot with surface temperatures reaching 200.000°C (against 5.500°C for our Sun!). Stellar winds from the revived star that's now fuelled by the heavier elements in its core generate a tremendous shock wave. You've probably already seen footage of a nuclear explosion where the shockwave blows everything in its surroundings to smithereens. Well, this is worse. About a gazillion times worse. The stellar winds from a "Wolf-Rayet" star can reach velocities of 3.000km... per second! They quickly catch up with the previously expelled gas bubble and cause such havoc as you can see on my sketch (note the bright central star at the centre of the nebulosity). In the end, the "Wolf-Rayet" star will collapse and explode as a supernova.

Such "Wolf-Rayet" stars are quite rare because they can only come from the most massive of stars, which are also rare because they don't form very often and have exceptionally short lives. It's estimated that there are only some 500 "Wolf-Rayets" in our Milky Way, 206 in M33 and only 154 in M31. Although the Andromeda Galaxy's bigger than ours, it doesn't contain as many supermassive stars because it has a much lower metal content.

The object of my sketch is called the "Crescent Nebula", or NGC6888 in scientific terms. It's a fairly difficult object at the heart of the constellation of Cygnus and needs quite a bit of telescope to be admired fully. But my binoscope clearly showed me the many ripples caused by the violent radiation of the central star. It lies 5.000 lightyears away from us.

Thursday, 6 October 2016

There are sooooooo many stars

A very wise person once said that the universe's so mind-bogglingly large that it would be a serious waste of space if it were just for us. The Sun's an insignificant little star among the 100 billion others in our galaxy alone (200 to 300 billion if you count in dwarf stars), and according to the best estimates astronomers can come up with there must be at least 100 billion galaxies in the universe. If you then consider that most stars have a planetary system, it would be most unlikely that we were on our own. After all, scientists are no longer asking themselves if there ever has been (or still is) life on Mars but when we're finally going to find undisputable proof of it and there are at least three or four other candidates for life in our solar system. So imagine how much other life there must be out there! Life, no matter how primitive, almost seems to be inherent to the formation of planets.

Take a look at this sketch... In the centre you see a galaxy (denominated NGC6928) comparable in size and shape to our own. Yes! That blob's just like our Milky Way and contains at least as many stars! It lies 200 million lightyears away from us and therefore we see it as it was 200 million years ago. The light that we now see from the galaxy started its journey towards Earth at the era of the Triassic-Jurassic mass extinction, the event that wiped out about 50% of all life on our planet, which in turn created the opportunity for the dinosaurs to become the dominant species. I'm telling you this so that you'd get the right sense of proportion.

On the top-left there's another galaxy (NGC6930), which is of the barred-spiral type (see here for explanation) and slightly smaller. But that's not all. If you look very carefully on the right of the main galaxy, you might see a faint little blob. Also that's a galaxy (NGC6927), but with a diameter of "only" 36.000 lightyears a fairly small one. Are we over and done with? No! Look on the top-right, between the two stars near the border. If you've got good eyes, you might see yet another little galaxy (NGC6827A) there. With a diameter of 17.000 lightyears it's rather a dwarf galaxy, but still it contains many billions of stars. Now go back to NGC6930, the brighter galaxy on the top-left. If you take a good look at its lower extremity, you may again see a kind of blob. Also this is a galaxy, a bit more distant, which lies behind NGC6930 and which scientists refer to as UGC11590.

That's all that I managed to see with my telescope and my eyes. Photographs of this area, on the other hand, will show you yet another, much more distant galaxy that lies exactly between the two main ones. The whole group of galaxies is travelling away from us at a speed of 4.100km... per second!

So how many stars are there in this view? There must be at least 1 trillion!!!! Just in this tiny little corner of our universe which I zoomed into at a magnification of 285x!

No, we're definitely not alone. The problem, however, is that communication with any extraterrestrial in one of those galaxies would be a bit slow because it would take 200 million years for our message to arrive.


Tuesday, 4 October 2016

The jewel inside the glitterball

Last week I talked about M15, the sparkling glitterball in the constellation of Pegasus. Well, today I'd like to take a deeper look into this beautiful globular cluster because it hides a tiny little secret. You need quite a bit of telescope, clear skies and a sufficiently high magnification in order to spot it between those thousands of bewildering stars but using a nebula filter you can't miss it. 

Most nebulae emit a large part of their light in a couple of very specific wavelengths of the visual spectrum, predomiantly ionised oxygen and hydrogen. Stars on the other hand emit light in all wavelengths. If you use a filter that blocks all the light, except for these very specific frequencies, the stars become significantly dimmer and the nebula leaps to the foreground. Such was the case when I magnified the M15 cluster to 507x and screwed the nebula filters on my eyepieces. The stars turned bluish and less bright, whereas a tiny patch near the top-left of the cluster's nucleus seemed to light up. This patch is a planetary nebula right in the cluster's core. It's one out of only four planetary nebulae that have been found inside globular clusters thusfar and was named after its discoverer: Pease 1.

So you see... the life of a star is the same all across the universe: they're born, life their life and when their fuel runs out they die, leaving a beautiful and bright cloud of gas for us to admire.

How to make astronomical sketches - Part 05

Here's the fifth episode of my video series about astronomical sketching: stars on the pc.


Thursday, 29 September 2016

Sparkling glitterball

No, this blog post isn't about a wild seventies' disco night. It's about globular clusters.

On public star parties, there's usually a little professor around: a cute little boy or girl that already knows everything about the planets and stars and who'd been moaning all day until his (or her) parents finally gave in and took him on a 50-mile drive to an incredibly remote spot in the mountains in total darkness in order to meet us astronomy goons. Obviously he can't wait to cast an eye into my telescope and so for starters I point it at a globular cluster. Then, before I guide him up the ladder, I assign him with a very important scientific mission: "Please, this is incredibily important! You have to count exactly all the stars that you see!"

Now have a look at my sketch and smile. There are about a hundred thousand of them :-)

Globular clusters are more or less spherical objects that contain many thousands of stars and which accompany our Milky Way, or other galaxies as well. These clusters are among the most spectacular objects in the sky, especially when observed through a medium to large telescope which allows you to distinguish all of the individual stars right into the cluster's core. This particular one, M15, is 175 lightyears across and lies more than 33.000 lightyears away from us. It's also one of the most compact globulars that we know as it has undergone a "core collapse". Scientists believe that there may be a black hole in it which caused this sudden contraction. Another surprising fact about globulars is that they're not young objects at all. Originally, scientists believed that they were made up of stars which had been ejected from our galaxy. But in reality they were formed at about the same time as our Milky Way, some 12 billion years ago, very similarly to the the formation of planets around newborn stars. However, star formation within the globular clusters began much sooner than within the galaxy itself and so they contain some of the oldest stars in the universe. Given that the universe itself is estimated to be some 13,8 billion years old, these globulars and their stars have been around for most of that time. In comparison, our Sun and solar system are "only" 4,5 billion years old. 

Globular clusters are also incredibly dense, as you can see on the sketch. Whereas the nearest star to our solar system lies 4,2 lightyears away, the stars in the globular's core are at least a thousand times closer to one another. If you'd like to know what it would be like to live in a globular cluster, imagine that the whole sky's filled with stars that are 10 to 20 times brighter than the full moon! Such an environment would be most unfavourable for planets because of the constant gravitational interaction with nearby stars and therefore it's highly unlikely that we'd find life there. But they remain unparallelled in beauty when observed from good old Earth.