Friday, 26 February 2016

The colours of the heavens

The night's sky is full of colour. It's just that we, poor humans, are having great difficulties to see them because our eyes are... well... almost useless at night. We've got very small pupils, relatively few light-catching cells on the retina and we lack the tapetum lucidum of the true creatures of the night which reflects the light back into the retina, thus doubling the eye's capacity to see in the dark. Many people who're looking in a telescope for the first time feel probably overwhelmed when they see the craters and mountains of the Moon and rejoice when they can make out details on the planets. But during the three decades that I've participated at star parties where the public could come and take a look at the heavens, their enthusiasm often faded when the objects I showed faded as well. Some deep sky objects are incredibly spectacular, such as the Orion Nebula or large globular clusters with their hundreds of thousands of stars. But after a while you have to start showing less impressive objects, such as galaxies, planetary or faint diffuse nebula and the "wows" and "ohs" quickly change into "can you show us Saturn again?". Not that Saturn wouldn't be breathtaking to look at with its elegant rings, but in the end I usually feel a bit disappointed because there are so many other things I'd like to show and which are just as spectacular in their own right, if you know the story behind them and you start to realise what exactly it is that you're looking at (with a certain difficulty). 

Alas, observing through a telescope is a work of patience, relaxing and letting your eye (or eyes in my case) adjust to the dark image. You also have to explain that it helps to look just next to the object because most of the light catching cells on our retinas are next to the point where we focus. But in these times of fast consumerism, patience is becoming a rare quality and I have to admit that I'm no better than anybody else in that regard, perhaps on the contrary. Most of the time, people will glance into the eyepiece for about two seconds and then happily exclaim: "Wow! I've seen it!". Believe me, these people haven't seen a thing.  

Returning to my topic, as much as we're useless at distinguishing light in total darkness, we're even ten times worse at detecting colour in the dark. That's because colour is perceived through a different kind of cells on the retina than those which capture light. As soon as the dark sets in, all colours fade to grey. This is probably another reason why many people feel disappointed after having looked through a telescope for the first time. We've been conditioned too much by all of the wonderful and immensely colourful pictures of our universe that we find in books or on the internet that we tend to forget that those are the fruit of many hours of exposure time and digital rendering. 

And yet... even with our poor little eyes there is a lot of colour to see up there. The object we look at just has to be sufficiently bright for us to be able to perceive the colour. Stars, for instance, are a perfect example. Many stars show a wonderful amount of colour if you take the time to appreciate it, from great red Betelgeuze, orange Aldebaran, yellow Capella (and our sun!), green Procyon, white Vega and bright blue Rigel. The colour of the star is a consequence of its temperature and contrary to what you might expect, red is cold and blue is hot! Think about the flames in a fire... the red flames, which you usually find at the edges, are the coldest, whereas in the heart of the fire the colour changes to yellow and even white. Blue flames on the contrary, like the ones from a gas stove, are extremely hot. The colour game of stars becomes even more spectacular when we're looking at double or multiple stars. Just look at the example on this sketch: Almach or scientifically Gamma Andromedae, the third brightest star in the constellation of Andromeda. It's a beautiful double with the main star being a yellow-orangy giant and its companion a smaller but hot blue star. The companion's actually a lot more complex than you'd guess at first sight because it's a double star on its own! It's sister star can be resolved with large telescopes (with larger magnification than I used here) given perfect sky conditions and it revolves around the other in a period of 64 years. But that's not all. The blue star is itself an extremely close double, the components of which orbit each other in a period of only 2,65 days! So in total, the Gamma Andromedae system is a quadruple star!

But this is only the beginning. In my next posts I'll show you more and very unexpected colours. I'm sure that you'll be amazed!

Wednesday, 24 February 2016

A shiny crystal ball

When the famous British astonomy pioneer Sir William Herschel pointed his telescope at it back in 1790, he was so amazed by what he saw that he had to completely rethink his idea about the many nebulous objects he had thusfar discovered. Until then, he had always held the belief that all nebulae or fuzzy objects consisted of stars that were simply too remote to resolve in a telescope. But here he saw a star that was clearly enveloped by what he called a "luminous atmosphere". And this observation turned out to be correct.

The Crystal Ball, or NGC1514 in scientific terms, is what's called a planetary nebula. This doesn't mean that there's a planet in it or anything, but rather that it looks a bit like a planet. Indeed, most planetary nebulae are small, round and do look a bit like a planet when observed at lower magnifications. In reality however, a planetary nebula is a shell of gas surrounding an old, dying star. The outer atmosphere of the star is expelled into space by powerful stellar winds, exposing its hot inner core which emits strong ultraviolet radiation. This radiation in turn heats up the nebulosity so much that it starts to emit light on its own and thus making it visible to us. A curious thing about this particular nebula is that its central star is extremely bright compared to the nebula itself. Usually the central stars of planetary nebulae are much fainter and sometimes even invisible to amateur telescopes. Recent studies conjecture that the central star in the Crystal Ball nebula is in fact a very close double star, two stars which orbit each other. In this case they're so close to one another that they're impossible to distinguish by any telescope we possess for the moment and that we can only conclude the presence of a companion star through mathematical deductions of our observations. The orbit of the companion is believed to be so close that it revolves around the main star in a period of only 10 days! So don't be fooled by the little star you see a bit to the upper-left of the central star on my sketch because that one's a lot closer to us than the nebula, which is well over 800 lightyears away in the constellation of Taurus.  

Nebulae like these are very important to the universe because they feed it with heavier chemical elements such as carbon, oxygen and nitrogen which were formed inside of their central star before it started to fall apart. We've also already been able to observe similar nebulae in other galaxies, which tell as a lot about the chemical composition of those. Most planetary nebulae are incredibly spectacular objects which reveal a great deal of detail in larger telescopes and at high magnifications, such as the various and complex gas shells. Unfortunately, due to circumstances beyond my control (well... actually it was all my fault because I'd made some "modifications" to my telescope which made it technically impossible to reach high mags) I couldn't push my telescope beyond 206x anymore. But the two main shells were clearly visible, as was their rather irregular shape. The faint nebulosity inside of these shells indicates that the star's still blowing gas into the nebula. Or in other words, we're testimony to its death struggle. That sounds very dramatic and in a certain way it is also a drama. The universe creates and the universe takes away. But one day perhaps a new star may be born from the ruin of this one.


Monday, 22 February 2016

On our way to the end of the universe

The universe is big. Or as Douglas Adams described it in his bestselling novel "The Hitchhiker's Guide to the Galaxy": you just won't believe how vastly, hugely, mind-bogglingly big it is. Scientists currently estimate its size to be 91 billion lightyears in diameter. However, this is obviously rather difficult to determine. Because how do we define our universe in the first place? Some say that the universe is everything within our space-time environment which could have a chance to interact with us and vice versa. How plausible this definition may seem at a first glance, it's also quite restrictive because some parts of the universe may expand faster than light can traverse it so any message we send will never arrive at its destination. That's a direct consequence of the speed of light being constant and finite and so far Einstein has always been proven right. So we must assume that regions of our universe exist which are just as much part of reality as we are but which will forever remain beyond our reach of interaction or observation. Therefore we'll never know how big the universe really is.

The part of the universe which we can interact with, on the other hand, is the observable universe and the edge of that is, indeed, almost 46 billion lightyears away, which makes it just over 91 billion lightyears across. This edge is very close to the actual age of the universe times the speed of light (13,9 billion lightyears), but this is not a correct representation since our galaxy and the edge of the universe have travelled substantially further apart since the Big Bang and our universe is still expanding at a breathtaking rate. 

Today, I want to show you some of the furthest objects that I've ever observed with my humble, homemade 18" telescope: a cluster of galaxies, scientifically denominated Abell 2666. I was able to identify 5 members of this cluster, with NGC7768 being the prominent one, near the centre of the field of view. The other 4 are a lot less obvious and I challenge you to find them all! :-) Contrary to some of my colleagues who try to sketch every little detail they thought they perceived during their observation, I try to give my audience an experience as close as possible to really looking through the eyepiece. The details are still there but you'll have to look for them very carefully, just like I had to do for a considerable time when I made my observation. The central galaxy immediately draws the attention, being easily visible with its 12.3 magnitude. The faintest on the other hand is close to mag. 16 and therefore at the limit of what you can expect to see through a similar telescope. NGC7768 is a fairly primitive galaxy and still fully under development. Analysis with the Hubble space telescope revealed a disk of dust and at least one star forming region. 

Imagine that every little patch you see on my sketch is a complete galaxy, just like Andromeda, Triangulum, the Pinwheel or our own. The distance of this particular cluster is estimated between 340 and 360 million lightyears, so at not even one hundredth of the distance to the edge of the observable universe! So yes... the universe is big!


Friday, 19 February 2016

The Cigar Galaxy and a Supernova

Every now and then, we are testimony of something so incredibly extraordinary that we can only explain it in math because our minds are simply too small to grasp the mindboggling facts. 

We all know that looking at our sun is bad because its brightness is such that eventually it'll burn your eyes. Now imagine... something 10 billion times as bright!!! That's a 10 with another 9 zeroes behind it! That's how bright a supernova can be! But wait a minute... What exactly is a supernova? In short, it's a massive star, much larger than our sun, which at the end of its life dies in a gigantic explosion. Its entire atmosphere is blown away into space, leaving only its core, glowing and slowly fading until it dies. If the star is massive enough and hence has a sufficiently heavy core, the explosion may even result in the formation of a black hole! More technically, at the end of the star's lifecycle, the nuclear fusion process which generates its energy becomes so unstable that it can no longer withstand the gravitational pull from its core. The star suddenly collapses and this shock causes the expulsion of the outer gas layers into space.  

Only five such events have been recorded by mankind in our own galaxy. The most famous of which were the one in 1054, observed worldwide and resulting in the notorious Crab Nebula, and the one which was amply observed and documented by Kepler in 1604 in the constellation of Ophiuchus, the snake bearer. Supernovae were important events because they convinced early scientists to abandon the old Aristotelian idea that the universe beyond the moon and planets never changed. Since then, many more supernovae have been observed in other galaxies and two years ago we were so lucky as to have one in the fairly close Cigar Galaxy, or also known as M82. When you look at my sketch, you'll immediately understand where it got that nickname from. It's a so-called "starburst" galaxy, which means that due to external circumstances, in this case the strong gravitational interaction with nearby galaxy M81, the galaxy's being pulled and squeezed all over. This interaction started about 100 million years ago and has gradually deformed M82, resulting in all of the galaxy's gas being funnelled into its core which in turn triggered an extraordinary rate of star formation, at least tenfold compared to normal galaxies such as our own. 

Two years ago a stunning supernova exploded within it, becoming so bright that it actually became visible to small telescopes and binoculars! Given its distance of roughly 12 million lightyears, that's quite an event. Yet, it's one of the closest supernovae observed in recent history, superceded only by the 1987 Tarantula Nebula supernova, which was only visible on the southern hemisphere and was 167.000 lightyears away. Yes, and the one in 1972 which happened 11 million lightyears away if you wish. But bear in mind, as I explained in my previous posts, that in reality the Cigar Galaxy supernova happened already 12 million years ago, much prior to the appearance of the first hominides on the african plains. On my sketch it's the bright little star within one of the galaxy's dark dust lanes. Observational data confirmed that in reality it should've appeared much brighter still but that much of its light was indeed blocked by that cloud of dust. It was first discovered on the 21st of January 2014 (although earlier photographs of the galaxy already show it) and reached its peak about a fortnight later, before beginning to fade again slowly. Soon after I made this sketch the supernova disappeared for us humble amateurs and its remnants can now only be observed with extremely large and professional instruments.


Wednesday, 17 February 2016

M101, the Pinwheel Galaxy and a little Relativity

There are at least 100 billion galaxies in the known universe. Imagine that! Some are smaller than our Milky Way, which is roughly 100.000 lightyears across, but many are much bigger such as Andromeda. The largest we know so far is designated as IC1101 and scientists believe that its size is a whopping 5,8 million lightyears across and that it contains at least 100 trillion stars (compared to 100 billion in our Milky Way). Now imagine that there are an estimated 17 billion Earth-like planets in our Milky Way alone and you'll certainly agree with me that there must be millions of other forms of (intelligent) life out there. Actually, some scientists are no longer asking themselves if there has been or still is life on Mars, but when we'll discover undisputable proof of it. Also Europa, one of Jupiter's moons, and Enceladus, one of Saturn's, seem to be highly probably candidates for extraterrestrial life. Of course, we shouldn't start the whole Roswell flying saucer hysteria all over again, or at least not for the time being. If there's life on other places in our solar system it's almost certainly quite primitive, such as bacteria or other micro organisms. But then again, if there's life, either intelligent or primitive, on even more than one planet in this tiny little solar system, how big are the chances that there are more forms of life out there in the universe than we can possibly imagine? 

Unfortunately, even if we do discover a star with a planet containing intelligent life, it's not going to be an easy conversation, as Carl Sagan perfectly described in his novel 'Contact' (cfr. also the film with Jodie Foster). Suppose that that star's 50 lightyears away from us, which still isn't our backyard but rather the terrace around our house in stellar terms. Then it would take our message 50 years to arrive! And what's more, we'd have to wait yet another 50 years in order to receive their reply! If we then consider that exceeding the speed of light is mathematically impossible (unless Einstein was completely wrong) and that in order to create a wormhole  shortcut through our universe (supposing that this theory is correct) we'd need an energy source at least the size of Jupiter, it's not that we can embark on an interstellar holiday cruise already tomorrow. And to stray completely from my chosen topic for this post, even if we were be able to take that cruise, it'd not be a merry homecoming since the Earth may have aged centuries in the meantime whereas to us the cruise only lasted a couple of weeks. Ah... relativity... the universe is all about relativity and about how incredibly insignificant we humans are, even though some still believe in their arrogance that we're the 'centre of creation', or whatever that may mean. Looking up at the night's sky instead of keeping your nose stuck in a dusty old book nobody knows for sure who wrote it anyway certainly teaches you to put things into perspective. 

To illustrate all of this, I've chosen this sketch of M101, nicknamed the Pinwheel galaxy due to its obvious spiral shape. It's also comparable in size to our Milky Way and therefore it gives us a very good idea of how our galaxy might appear to an inhabitant of the Pinwheel. Although it seems to be much more active than ours and numerous incredibly large stellar forming regions have already been discovered within it. It's not really visible on this drawing but the galaxy's slightly deformed due to gravitational interaction with its 5 major companions, all of which are quite smaller than the prominent galaxy of their group. It lies 21 million lightyears away, almost ten times as much as Andromeda! Or in other words, we see this galaxy as it was when North and South America were still separated, India had only recently begun crushing into the Eurasian plate (forming the Himalayan) and the first ape-like primates appeared. And this is still close by! How about that for relativity? 

Tuesday, 16 February 2016

M33, the Triangulum Galaxy



Thursday, 11 February 2016

M31, the Andromeda Galaxy

The Andromeda galaxy is the nearest major galaxy to our own and it's actually the largest in our local group of galaxies, which contains the also famous Triangulum galaxy (M33) and at least 44 other, smaller members. Recent studies show quite different results but we can assume that the Andromeda galaxy is easily more than 50% larger than the Milky Way and that it contains a lot more stars too. It's 220.000 lightyears across, twice as much as our own galaxy, and that still isn't big at all if you compare it to some of the giant galaxies out there. 

If you look up at the autumn sky you can't actually miss it since it's certainly visible to the naked eye, unless you're observing from a city centre. It's easy to find, just above Mirach (Bèta Andromedae) and if you've got a pair of binoculars you may even see two of its companions: M32 (to the left on my sketch) and M110 (a bit further out to the right). Both are mini-galaxies that accompany their master, much like the Magellanic Clouds, which can be seen on the southern hemisphere, are dwarf-galaxies that accompany ours. The distance of this galaxy system is estimated at 2,5 million lightyears and this brings me to an interesting thought. 2,5 million lightyears means that light, with its formidable speed, needs 2,5 million years to travel from the Andromeda galaxy to us. As a consequence we don't see the galaxy as it is now, but as it was 2,5 million years ago. Yes! The image of it that has reached us today actually left the galaxy when the first humanoids appeared on the African plains! We haven't got a clue what the Andromeda galaxy, or by extension any other star or object in the night's sky, looks like today. For as far as we know, it may already have blown up! Of course, a galaxy the size that it is doesn't disappear overnight and we can rest assured that it's probably still there. However, some other stars or objects may have disappeared, or appeared without us knowing it. We can only wait until the light from those events has eventually reached us. 

In summary, looking at the night's sky actually means looking into the past, because everything that you see doesn't exist anymore as it is today. The closest star, Proxima Centauri, is only 4,3 lightyears away so we see it as it was 4 years ago. But the further we look into the universe, the further we look back into time. Isn't that exciting?

Another interesting thing is that the Andromeda galaxy's heading towards us. It's expected to collide with ours within 3,75 billion years. That's still a lot of time and that doesn't necessarily mean that some star's going to crash into us. Most of the space in a galaxy is absolutely void (think of the distances between us and the closest stars) and therefore collisions are highly unlikely. Most probably, as is the case with other colliding galaxies, the two will simply merge through gravity into a single, giant galaxy.     

I know that my observation seems a bit out of season. But the Andromeda galaxy happened to be at a very comfortable altitude above the horizon for my binoculars so I couldn't resist it. There was a fair bit of wind which gave me some trouble but the sky's transparency was excellent. I immediately noticed the dark dustlane on the right and the two companions just leapt out at me. Mind you, the stars you see, also the ones "within" the galaxy, are much closer to us as they all belong to our own. A galaxy's so far away that it's impossible to distinguish any individual stars in it, at least not with an amateur telescope. 

Tuesday, 9 February 2016

NGC1647, another lovely cluster in Taurus

If you've got a nice pair of binoculars, nothing's more pleasing than surfing the sky with it, in search for one of the thousands of jewel boxes up there. This particular star cluster close to Aldebaran, the orange eye of the bull, doesn't appear particularly rich. Estimates suggest that it doesn't contain more than 200 stars and not even half of them are visible to us. The problem is that the cluster lies partially behind a dark dustcloud which seriously impairs our vision of it. And yet it's a real beauty with its large number of cute double stars which fill the centre of the field of view. 

Sky conditions weren't ideal when I made this sketch but still I think that I got most of the stars that are possibly visible with my Nexus 100 astronomical binoculars. The cluster lies at almost 1.700 lightyears in our arm of our galaxy. It definitely deserves a bit more attention since it's such an easy and noteworthy object. About thirty of its stars are brighter than the 11th magnitude, so it's within reach of even the smallest telescopes or binoculars.  

Monday, 8 February 2016

NGC1807-1817, the little Double Cluster in Taurus

Yes, also the constellation of Taurus has its double cluster. Perhaps it's not as famous as the one in Perseus (NGC869-884 of which I wrote earlier), but it's certainly beautiful in its own right and without any doubt worthy of our attention. These two, which may have originated as a single cluster that later split up, are quite old. Whereas the Perseus double cluster's still very young with its 13 million years, the Taurus' one is actually between 0,8 and 1,2 billion years old. Not quite as old as our Sun, which is now a middle-aged star at 4,5 billion years, but for a cluster this is still quite remarkable. Most clusters dissolve over time under the gravitational infuence from our galaxy and the individual stars each go their own way. This cluster on the other hand has remained surprisingly compact. The ageing process of its stars is also much faster than that of most ordinary stars and some of them have already reached their red giant stage. Stars transform hydrogen into helium through fusion, the energy source which makes them emit so much light and other radiation. But at a certain point they'll run out of hydrogen and start fusing helium into carbon, oxygen or nitrogen. This causes the stars to expand greatly (when this'll happen to our Sun within 5 billion years it'll swallow up Mercury and Venus and the Earth will be scorched by its atmosphere) and cool further down. Young stars are hot and emit blueish light, just like blue flames are much hotter than yellow or red ones. But over time they cool down and change colour, becoming white, green, yellow, orange and eventually red. I could easily distinguish at least two orangy stars in the left cluster (NGC1817). Please don't consider the big orange star in the foreground because it's not part of the clusters at all! It lies at a distance of 343 lightyears whereas the clusters are a whopping 6.400 lightyears away from us, in the opposite direction of the centre of our galaxy.

So through my sketches I've granted you a view of the different stages of star cluster formation, from the newborn baby stars within the Orion Nebula, over the young Perseus double cluster, the Pleiades that are currently breaking up and this old one. 

This little double cluster's easy to find on the border between Taurus and Orion and is within reach of even a small pair of binoculars, although in order to resolve the entire cloud of tiny little stars in the background a somewhat bigger instrument's required. For those who want to leave the beaten track...

Friday, 5 February 2016

IC2118, the scary Witch Head

The Witch Head Nebula, hence nicknamed because of it's particular shape (upside-down on my sketch), is perhaps an example that in our universe sometimes a catastrophe can lead to something beautiful. The scientific community believes that this particular nebula is in fact the remnant of a supernova explosion, a cataclism in which a dying giant star blows its entire atmosphere into space. The cloud of gas and dust is all that remains of this event, and in this particular case so much time has passed that the gas has cooled down up to the point that it doesn't transmit light anymore on its own. However, that's without taking another nearby giant into account: Rigel, the bright blue left knee of Orion. You can't see it on my sketch because it was a bit outside the field of view of my binoculars (to the bottom left), but this enormous and very hot star illuminates the nebula so much that we can see it. Its shape also indicates a strong influence by the star, the stellar wind of which clearly ripples it, as if it'll never be allowed to rest in peace.

But is this the end? Has the old star just died without leaving anything else but its ashes spread across the galaxy? No! Recent research has shown that many parts of this gas cloud are contracting again under its own gravity and... that new stars are forming within it! So with time the Witch Head Nebula may become a bright stellar nursery, just like the Orion or Monkey Head nebulas of my previous posts. Isn't astronomy something beautiful?

This drawing has been high on my wish list for a long time but for some strange reason I've never really got to it. And when I did, sky conditions were always such as to impede any serious observation. But yesterday evening the sky was particularly transparent after the storm of the day before so I had another go at it. I had expected a very difficult observation because the nebula's incredibly faint and usually only visited by photographers who're able to capture it after many hours of exposure time. But yet, with some careful looking the patch around the central star appeared quite easily. And after some time and adapting myself fully to the dark, also the two "wings" revealed themselves, with the top-left one slightly brighter than the bottom-right one. Also the bright border, the one illuminated by Rigel, was quite pronounced, whereas the rest of the nebula faded in to the background towards the top-right.

All in all I'm quite pleased with this observation and I hope that you like it too. It's a very difficult object and given its enormous size a pair of big binos must be the perfect instrument for the job. As always I didn't want to make things too easy for my public so I've tried to create more or less the same challenge for you as it was for me behind the eyepieces of my binoculars. Enjoy!  

Wednesday, 3 February 2016

Street lights: an incredible waste

We've always assumed that street lights protect us against criminals and that they seriously reduce the number of traffic accidents. But new research actually indicates the opposite, i.e. that turning the lights off doesn't result in a higher crime rate or accident statistics at all or on the contrary, that it even results in much less burglaries or accidents. There are a good number of arguments that support this theory, which I demonstrate in the video below, because seeing the effect of turning the lights off will convince you more than me explaining what happens.

Moreover, several studies have linked artificial lights directly with cancer, placing it just below the risk level of asbestos! The argument goes that specific wavelengths of artificial light suppress the production of melatonin, the hormone that is responsible for regulating our sleep. This particular hormone has the capacity to absorb free radicals and other cancer-generating substances and it can even shrink and kill entire cancer cells. Therefore, suppressing the production of melatonin makes us much more vulnerable to cancer.

On top of that, artificial light has a devastating effect on animal and plant life, destroying their biological clock. Sea turtles can't find their way home anymore, migrating birds fall under the spell of brightly illuminated buildings and die of exhaustion, many insects and other animals are attracted to our lights and become a too easy prey for predators, fireflies or other animals which use light as a means of communication suddenly lose track of each other, frogs refrain from singing their love chorus under the glare of artificial light and stop reproducing, and so on. The effect of all this on the Earth's ecosystem is so far completely unknown, but in our arrogance we assume that with time all animals and plants will adapt to our desire for light. If you ask me, that's a serious risk we're taking.

And to round it off, noone actually has any idea how incredibly big the energy consumption needed for our night lights actually is. For a medium-sized country like Italy, the energy required for its public lighting is estimated at a whopping 900 Million kWh, making public lighting overall by far the biggest consumer on the planet! Imagine how much this costs us, not just in terms of money, but also in terms of damage to the environment. Electricity has to be produced somewhere and for such an enormous need a couple of solar panels (which don't work in the dark anyway) won't do. In stead, traditional coal and gas power plants have to continue operating at night with dire consequences for global warming. 

And all of this... just to appease our completely superfluous animal instinct which tells us to be afraid of the dark, whereas the dark actually protects us. 

I'd call that insane. But who am I...

The Italian version...

Tuesday, 2 February 2016

M42, the mighty Orion Nebula

Orion's certainly the most prominent constellation of winter and it holds one of the greatest night sky treasures visible in the northern hemisphere: the famous Orion Nebula. It's easy to find, below the three stars in Orion's belt, at the middle of a string of small stars we call the "sword". If you look carefully, you can already see it with the naked eye under a not too much polluted sky. The total nebula extends over an area of 1°, or about two full moons across, but in reality it's just a part of a much larger nebula complex, including the also famous Horsehead Nebula, the Flame Nebula, M78 and gigantic Barnard's Loop which draws half a circle around the entire constellation. 

The Orion Nebula is a schoolbook example of a stellar nursery and observations have revealed up to 3.000 newborn stars at several stages of their formation within it. Stars are born when large clouds of gas and dust collapse under their own gravity and the heat generated by their compression ignites nuclear fusion. The best known baby stars within this nebula are without any doubt the so-called "trapezium", four bright stars which are so close to one another that in the large field of view of my binoculars they could hardly be separated. Some of the brightest stars we see in this nebula may only be 10.000 years old, which in stellar terms is extremely young. The Hubble space telescope also revealed so-called protoplanetary disks, which is a disk of hot gas and dust surrounding a newly formed star. Gravitational collapse within these disks results in the formation of planets. Given the sheer number of these disks that we've already discovered, scientists conclude that stellar and planetary formation is very common in our universe.

The nebula will have evaporated completely within 100.000 years due to stellar radiation and the star cluster which was formed within it will start its journey through space, eventually falling apart as well. The Pleiades of which I spoke in an earlier post are a perfect example of such a young cluster that's just emerged out of a similar nebula, the remains of which have already evaporated. Although the evolution of our universe appears extremely slow in comparison to the lifespan of a man or even the entire human civilisation, the total lifespan of such a nebula would be no longer than 30 million years, meaning that the Orion Nebula must've formed much later than the age of the dinosaurs and even later than the Eocene. It is believed that some stars which can now be found in nearby constellations such as Auriga, Aries and Columba in fact originated from this nebula and are still zooming away from it at a speed of 100 km/s. It's also odd that not a trace of this nebula can be found in any written account before the beginning of the 17th century. Ptolemy for example didn't mention it, although he did mention other (fainter) nebulous objects in the sky. Galilei noted the trapezium but didn't mention the nebula either. It is therefore believed that a current flare-up of young stars causes a temporary increase of the nebula's brightness.

The Orion Nebula is one of the few large nebulae with a high enough surface brightness to reveal colour to the human eye. With my binoculars I noticed a very faint blue-green hue, which is actually the first colour that our eyes can perceive in darkness and which is caused by doubly ionised oxygen in the nebula. But with my old 18" Dobsonian reflector I was also able to see a very faint reddish tint near the brightest edges.

Almost attached to the great Orion Nebula, you can see its smaller companion: M43, and a bit more towards the top the "Running Man Nebula". The dark dustlanes within it do show the silhouette of a running man in a serious telescope but obviously my binoculars are not powerful enough to show all of that detail. The faint glow around the bright star below the nebula, is NGC1980, another part of the Orion cloud complex.