Saturday 24 December 2016

Towards the edge of our galaxy

Our galaxy, which we call the Milky Way, is some 100.000 lightyears across. In kilometres, that would be more or less! Our solar system lies in one of its less fashionable parts, in the heart of a spiral arm that's not even worthy the name. Astronomers refer to it as the "Orion Spur", because our part of the Milky Way's most visible in the constellation of Orion and because, as I said, it's not a full-grown spiral arm but a sort of spur in between the Saggitarius and Perseus arms. On the image below you can see an artist's concept of our galaxy and I've highlighted the position of our solar system with a red dot.

With my sketch, I want to take you towards the edge of our galaxy, towards the yellow dot on the map. Because there, 15.000 lightyears away, lies a beautiful open cluster, called NGC1193. It's a fairly difficult object because of its distance, but also because a lot of its light is being blocked by the dust of the large Perseus spiral arm. And yet, there it is... a middle-aged cluster which is slowly falling apart and stars that are beginning to leave the nest in which they were born. 

And with this, I'd like to wish all of you a Merry Christmas and a very Happy New Year. After a year of activity, my blog has grown considerably and that's all thanks to you, my dear, loyal readers. I hope you enjoyed my posts and I can assure you that I'll do my best to do even better next year. All my best wishes to all of you!!!


Thursday 22 December 2016

Stars in another galaxy

Have you ever wondered what the universe would be like in another galaxy? Well, the answer's quite simple: very similar to our own. Of course, every star's different and there are probably planets out there so weird that not even the wildest science-fiction writer could've invented them. But basically the universe's quite the same everywhere. Stars are what they are... big stars, small stars, hot ones and cold ones. Most will die quietly as planetary nebulae, others are so massive that they'll explode as supernovae. But all of them are born in huge hydrogen clouds. I've already shown you many examples of these star-forming regions, such as the famous Swan Nebula and I've even made a video about flying into the Orion Nebula

But let's go back to my previous sketch, the one about the Triangulum Galaxy (M33). On the bottom sketch I've added labels to highlight some of the star forming regions in that other galaxy which are already visible to ordinary amateur telescopes. Each of these bright knots in the galaxy's spiral arms is a nebula complex, similar to the Orion, Swan and other star-forming nebulae. Inside those knots, baby stars are born. 

By far the biggest of these nebulae in the Triangulum Galaxy is the one on the far left, which astronomers refer to as NGC604. Can you believe that this nebula's so big that it's 1.500 lightyears in diameter? That's the distance from the Orion Nebula to Earth! This makes it probably the biggest nebula complex in our entire local group of galaxies! Encouraged by the spectacle I observed at low magnification, I pushed the binoscope to 507x and pointed it at NGC604. What I saw nearly made me tumble on the ground (and I was standing 6 steps up on a ladder). Not only did I see some incredible detail in that nebula (the slant "H" or "M" really stood out), I was able to see individual stars in it! They were impossible to pinpoint exactly - they were so tiny and they seemed to be "dancing" across the nebula - so on my sketch I just put some random dots to give you the idea. But I did see them!

I had always assumed that it was impossible to see individual stars in other galaxies with an amateur telescope because they're simply too far away. The Triangulum Galaxy lies at a distance of 2,8 million lightyears! But I was wrong. It is possible with a sufficiently big telescope and good sky conditions. 

These dots are bright and hot baby stars, much like the trapezium stars in the Orion Nebula. One day planets will form from the debris around them (if that hasn't already happened) and they'll start their journey through their galaxy like our little Sun's flying around our Milky Way's centre. So you see... the universe's pretty much the same everywhere.

Tuesday 20 December 2016

M33 revisited

Almost a year ago I wrote about M33, the famous Triangulum Galaxy. The sketch I presented at the time was observed through my 100mm astronomical binoculars, which is in fact one of the best instruments to use on this object. The galaxy spans an area of almost 4 full moons in our sky, meaning that its light's dispersed over a large area. Therefore it appears very faint and doesn't support high magnifications well. An ordinary pair of binoculars, on the other hand, has a relatively low magnification compared to the combined aperture of its lenses and will show the galaxy as a small but reasonably bright smudge. Remember what I told you about magnification! Suppose the total amount of light a telescope can capture of an object is one of these mini jars of jam you get in a hotel. When you spread the jam on one slice of bread (small surface - low magnification), you will taste the jam quite well. But when you spread it on a whole loaf (large surface -  high magnification), its taste will hardly be noticeable. 

A telescope often struggles with these large and extremely faint objects and with good reason too. The main job of a telescope is not to magnify, as many people think, but to capture as much light as possible, concentrate it and let it all fit into your eye. The bigger the lens or mirror of a telescope, the more light it can capture and the better you'll see the object. But... every telescope also has a minimum magnification which is directly related to the size of its lens or mirror. If you go lower, not all of the light that the telescope captures will enter your eye anymore because its "exit pupil" will be too large. The "exit pupil" is the little image disk that comes out of the telescope and which you can observe. If this disk's larger that the pupil of your eye, some of its light will be lost and this would be the same as looking through a smaller telescope. If we suppose that the pupil of a young person can open up to 7mm in the total dark, a telescope with an 18" mirror has a minimum magnification of 65x. Below that, the "exit pupil" will be larger than 7mm and hence be larger than the pupil of your eye. An 8" telescope, on the other hand, can go as low as 28x, or 2,3 times less than the 18" telescope. At 28x the object will appear 2,3x smaller but also 2,3x brighter than at 65x. Of course, an 18" telescope gathers 5 times more light than an 8" telescope so it still holds the advantage over its smaller brother. 

Now let's talk about a binoscope. In theory, its combined optical tubes gather as much light as a telescope of 1,41 times its diameter. An 8" binoscope therefore has the same performance as an 11,3" monocular telescope. But... with the 8" binoscope you can go as low as 28x, whereas the 11,3" telescope has a minimum magnification of 41x! This is one of the biggest advantages of the binoscope: the same light gathering power and optical resolution as a much bigger monocular telescope, but with a much lower minimum magnification. 

If you want to know what this means for our large and faint galaxy, here's my sketch of M33 through my 18" binoscope:

Not only did I see the spiral arms in a way that I've never seen before, many bright star forming regions in the galaxy really stood out. Here's the sketch with labels:

In my next blog post I'll take you a bit closer...

Thursday 15 December 2016

Bethlehem's star

Some time ago someone asked me what the actual star was that appeared at Jesus' birth. It's a question that has occupied the minds of many scholars and religious leaders over the last millennia because when you go back to the period of Jesus' birth, let's say from 10 to 1 BC, you come to the conclusion that nothing interesting at all happened from an astronomical viewpoint.

Some say that it was a comet, but for as far as we know there were no bright comets in that period. Perhaps there was a one-off bright comet - certainly not all of them have regular orbits - but its appearance hasn't been recorded by anyone. 

Some argue that it was a supernova explosion, but this is impossible because these explosions always leave a visible trace in the sky

During the last 50 years, there have been ever more claims that the star wasn't a real star at all but in fact an unusual position of one or the other planet in one or the other zodiac sign. These claims are again very unlikely because they're always based on greek astrology - which is unfortunately still being used today - whereas the magi or 3 kings came from Persia. Just for your information, babylonian and persian astrology was completely different from its greek counterpart and was based on a system of 17 or 18 zodiac signs. This means that all of these planet-zodiac theories are based on the wrong information.

But there's an even bigger mystery that none of the above possibilities can explain, i.e. how it was possible that the 3 kings who came from the east and who followed a star in the east could still end up in Bethlehem, in the west?!

The answer has only been discovered recently, in the 1980's if I'm not mistaking, and it's actually very simple. In order to explain it in a way that everybody can understand, I've created this small video. 

Enjoy and... Merry Christmas!!!


Friday 9 December 2016

A little butterfly

You may recall my blog post on the famous Ring Nebula (M57), in which I explained that this nebula's not a ring at all but a cylinder that we coincidentally see face-on. Today I'd like to present a very similar planetary nebula, but one that we see edge-on: M76 or the "Little Dumbbell", due to its resemblance to the much bigger and brighter Dumbbell nebula (M27). Personally I prefer to call it the little butterfly for obvious reasons.

On my sketch you can clearly see the bright central cylinder or the body of our butterfly The axis of the cylinder coincides with the rotational axis of our dying central star (which I couldn't identify during my observation). As I've explained before, the star's rotation causes an accumulation of matter along its equator, making it more difficult for the hot gas to escape from there. That's why many planetary nebulae have an elongated inner structure, or in extreme cases such as this become cylinders. 

The butterfly's wings on the other hand were formed much earlier, probably when our star was still a red giant that was running out of fuel and became unstable. It began to expand, cooled down, contracted under its own gravity, heated up and expanded again, blowing out large quantities of gas in the process. A good example of a star in this phase, ableit ten times more massive, is Betelgeuse. Eventually the star collapsed, expelling what remained of its atmosphere into space (the central cylinder). 

It's one of Messier's faintest objects but still surprisingly easy to observe, also in small telescopes (which may not reveal the "wings"). To my personal taste it's also one of the most beautiful planetary nebulae and every autumn night when I'm out under the stars I pay it a visit. It lies some 2.500 lightyears away from us and is headed towards us at 19km/s.

Monday 5 December 2016

The flying ghost galaxy

Those who've been following my blog have already been testimonies to many dramatic events that happen in the Universe around us. I've shown you the birth and the death of stars, supernova explosions and galaxies that have been ripped apart by unimaginably strong tidal forces. Today, I'd like to share a sketch of another incredible event: two galaxies that are crashing into each other!

NGC520, or popularly named the "flying ghost galaxy", is an object that's within reach of small telescopes under a dark sky. Right from first glance you'll notice that something's not quite right with it. It doesn't look like an ordinary galaxy at all, with a clear nucleus and spiral structure around it. A larger aperture telescope reveals the true nature of the cataclysm that started some 300 million years ago and that's now reached its most spectacular stage. Two nearby galaxies were attracted so much to one another by their mutual gravitational forces that they collided. However, you shouldn't think of this as the collision of two cars in a big fire ball. Given the enormous distances between the individual stars in a galaxy, it's highly unlikely that, when two galaxies meet, their stars will crash into each other. They'll simply fill the void and in the end the two galaxies will merge into a new and much bigger one. That being said, the tidal forces that these crashing galaxies generate, will seriously stir up the new entity and in turn this will lead to a burst of new star formation. 

Think of a galaxy as a cup of coffee with milk. Older galaxies that don't interact with others stop moving and become plain... the coffee being brown and uninteresting. Star formation comes to a halt. In younger galaxies - imagine these as coffee to which you've just added the milk - the gas clouds swirl and contract in the gravitational vortices, leading to the formation of many new stars. In the particular case of our flying ghost galaxy, the collision has added fresh milk and the gravitational pull is giving the whole a really good stir. Expect to see an explosion of new star births there!

The collision of galaxies is certainly not a unique event. Actually, in about 3,75 billion years the nearby Andromeda Galaxy is going to crash into ours! Our Sun will almost have reached the end of its life by then and honestly I don't think there will still be humans around to witness it, but as I explained, it won't be the end. It will be a new beginning.

Friday 2 December 2016

Street lights are destroying our lives

I've already written a lot about street lights and the adverse effect they have on our lives. I've even published a video to demonstrate that they actually reduce road safety instead of increasing it and that they make life a lot easier for burglars. Recent studies have also demonstrated a direct link between street lights and cancer! In spite of all this, tax payers around the world are still willing to cough up billions of €/$ to keep them burning.

But so far I haven't mentioned the biggest damage they cause to our planet yet, and with good reason too because most people couldn't be bothered less. I'm referring to the devastating effect street lights have on the greatest spectacle of our planet, the greatest work of art that any man has ever beheld: the night's sky. 

Most people have never really looked up. They're so busy with their own little lives, making as much money as possible, gathering a million likes on Facebook and commenting on the painfully stupid but yet incredibly important cows in the reality shows, that they seem to forget that their lives actually mean nothing at all. What is Earth anyway? A planet so insignificantly small that it would already completely disappear in the Sun's glow to an observer on Uranus. And our Sun's such an amazingly insignificant little star that it would not be visible to the naked eye anymore from a distance of merely 50 lightyears. That's hardly the doorstep to our backyard! 

Only those fortunate enough to have visited one of the ever rarer really dark places on Earth, a remote desert for example, realise what we've been missing over the last 60 years. Take a plane to Arizona, Namibia, the Sahara or Central Australia and you'll know what I'm talking about. It would be a useful lesson in humbleness that all of us should take. Just look at that incredible blanket of millions of stars and our Milky Way that shines down upon you like a bright string of clouds from horizon to horizon and you'll know that I was right.   

To show you the damage street lights have caused to our night's sky, I'm proud to present the work of Martijn, a Dutch astronomy friend and a highly talented artist. He made this series of 4 sketches of the Andromeda galaxy, the closest galaxy to our own, from 4 different locations. The first from his home town and a full Moon, the second from his home town without Moon, the third from a nearby somewhat darker location and the last from a place that we astronomers call "decent" (but far from perfect). What a difference, isn't it? Isn't it about time we switch those useless light off?