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.

Wednesday, 4 January 2017

Galactic tango

The tango's the dance of lovers. It's a subtle game between two passionate souls who spin and turn by their mutual forces of attraction, without yielding, until they finally succumb and the two become one. 

Now look at the two souls on my sketch. They're two reasonably small galaxies, some 26 million lightyears away from us. On the left lies NGC672, our gentleman who's leading the dance, slightly larger than his female partner on the right (IC1727). Both are very active and passionate galaxies with a large and bright central bar. NGC672 shows very delicate spiral arms, the upper one of which points to the lady on the right. 

IC1727's leaning backwards, in a classical quebrada movement. She's still resisting, but the attraction of NGC672's too strong. Her spiral arms have become twisted, irregular, the ends bending towards her lover. They're ready for the final encounter but it won't be a happy end. They'll have one last spin and then the bond will be broken. The centrifugal force of the scissors movement will break the magical embrace of dark matter that's connecting the two. IC1727 will do a pasada and then swirl away behind NGC672. Unfortunately, the two won't become one as is the case with the Flying Ghost Galaxy. But the tidal forces of the close encounter will mix up the matter in both galaxies so much that they'll be bursting with new stars. 

A one-night stand... but a lot of new life...

Isn't astronomy romantic? :-)

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 1.000.000.000.000.000.000km! 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!!!