Wednesday, 30 March 2016

Double Rammy

Aries, the ram, is a boring constellation. It's small and it doesn't have any striking stars or star configurations which makes it stand out between all of its brighter neighbours. Actually, my brother always referred to it as the "vaccuum cleaner" because according to him that's what it looks like and he does have a point. Yes, it houses a couple of interesting galaxies such as NGC772, but for the rest nothing worth noting. 

However... there's a very nice and challenging double star to be found in it, scientifically denominated 1 Arietis. Under a really dark sky it should just be visible to the naked eye, a tad above Beta Arietis. When you zoom into it with a telescope, and a sufficiently big one I'd suggest, it will reveal a very close companion. In scientific terms, the separation between the two is only 2,8 arcseconds and believe me, that's entering the realm of the big boys. 

Observing close double stars will immediately reveal whether your telescope has decent optics and whether the optical components of your telescope are well aligned (or "collimated" as we astronomers say). If your telescope's of poor quality, the main star of a close double looks that blurry that it disguises its companion. If on the other hand your optics are good, the companion will appear separated from the halo of the main star. Contrary to what you might expect, a star doesn't appear as a real point in a telescope, especially at high magnifications. Yes, stars are so far away that they should look like a point and not like a disk with a perceivable surface. And yet they do show a surface through a telescope, even when you've got perfect optics. In fact, this is an optical illusion caused by the characteristics of light. As you probably know, light acts like a wave which has tops and bottoms. When it passes through a narrow opening, like the lens of a telescope (yes, even a big lens or mirror has to be considered as a "narrow opening"), it will cause diffraction and create a strange pattern when magnified: a small central disk surrounded by rings that fade as their distance to the central disk increases. For more information about this phenomenon, click here. The result of all of this theory is that apart from the glare that a bright star causes, it will also appear as a disk with rings around it which may impede you from seeing a very close and faint companion. In the case of 1 Arietis I was still able to see quite a bit of black between the main star and its companion. But once we're talking about doubles that are less than 1 arcsecond apart, the stars may look as if they're glued together or the companion may become invisible altogether. 

In theory, the bigger a telescope, the smaller the diffraction pattern and hence the bigger its resolution power. Some people argue that the best telescope for this kind of high-resolution work's a big and high-quality refractor, but I strongly disagree. It's difficult to find a lens telescope with an aperture over 6 inches and they quickly become terribly expensive, whereas you can have a high-quality newtonian reflector that has three times the diameter of the refractor for only a fraction of the cost. Bigger aperture means that you'll see more and this also goes for objects where optical quality is vital, such as these close doubles. Of course, there's also a party pooper around which is called the Earth's atmosphere. Often our atmosphere will not be as steady as we'd wish and its turbulences will be so bad that not even a 100-yard telescope will allow you to separate a double star. The optical resolution is always limited by the resolution of our atmosphere. But if on a night with lots of turbulences ("bad seeing") you can't separate a double with a €5.000 18" reflector, you won't be able to separate it with a €20.000 8" refractor either.

Returning to 1 Arietis, I was able to see some yellow-orangy colour in the main star and when I did some research afterwards this was confirmed. It's an old giant star that's nearing the end of its life. The companion's much younger and hotter and appears clearly white. The brightness difference between the two isn't very big (magnitude 6,4 and 7,2 respectively) and yet it did look a lot bigger when I made this observation. But obviously a brighter main star will make a less bright companion look a lot fainter, so I guess that this sketch looks fairly realistic. The couple's 590 lightyears away from us and eagerly awaits your visit next time you're out under the stars. They surely deserve it.

Tuesday, 22 March 2016

What to do when the Moon's around

Most people consider the moon to be something wonderful and enjoy its blue rays of light that illuminate the fields of our countryside. The moon's like a friend walking you home on dark nights, making you less afraid of the imaginary dangers that may haunt you otherwise. As I explained in my post about public lighting, in spite of 3 million years of evolution, we still remain animals that are afraid of the predators that lurk in the dark. 

Of course, the Moon's beautiful to look at, especially with a telescope that will reveal its barren landscape of craters, canyons and mountains. The problem is however that when the Moon's around you can hardly observe anything else. That's because it reflects so much sunlight that most of the other objects in the nightly sky fade in its bright glare. Star clusters become less rich and sparkling, nebula filaments become ghosts of what they once were and distant galaxies disappear completely. So as much as the Moon may be pleasing to most people, many astronomers would like to fire a nuclear missile at it in order to blast it to bits. I consider myself fortunate to live in Italy where the climate's still fairly favourable and where I'm sure to get at least a couple of excellent observing nights a month. When I was still living in good old Flanders with its many weeks of rain and wind, being an astronomer could be very frustrating at times. If you then consider that for about 10 days a month the Moon will make observing difficult if not impossible, you'll understand why I only had about 10 really great nights... a year!
But... let's not overreact. Of course, deep-sky observing (nebulae, clusters, galaxies,...) is not the thing you'd want to do during a full Moon. But there are some interesting alternatives that can turn a moonlit night into a surprising observing success. One of them is planetary observing. I'll discuss this more into detail in the future, but planets are bright objects that don't suffer much from moonlight. Perhaps you'll lose a bit of contrast but nothing worth mentioning. That is... if there are planets around, because that's not always the case. Don't panic! One kind of objects will come to your rescue: double stars! I already mentioned double stars in my post about colour and just like planets they're generally bright and don't lose anything of their beauty during moonlit nights. The example I want to present today is Sigma Orionis. It's not just a double star, oh no! It's a quintuple star! The central star's already easily visible with the naked eye, just under Alnitak, the left star of Orion's belt. Actually, this central star's a double star - denominated "A" and "B" - but so close that it's impossible to separate with amateur telescopes. They're two very young stars, approximately only a couple of million years old, and they're quite massive too: 18 and 13,5 solar masses respectively. They're only 90 Astronomical Units apart, meaning 90 times the distance of the Earth to the Sun. Or to give you a better idea still, that's just over 2 times the distance to Pluto when it's farthest away from us. Since we're talking about such big and incredibly bright stars, you'll understand that this is pretty close. They orbit each other in a period of 170 years and also this is quite fast if you consider that Pluto takes 248 years to orbit our Sun.
Number three - denominated "C" - is that little star just on the left of the main star (or inseperable pair as I explained). It's a white dwarf which roams at a distance of 3.900 Astronomical Units (Earth-Sun distances) from the central pair. The two stars on the right, "D" and "E", lie at 4.600 and 15.000 AU respectively. Both of them are roughly 7 times the size of our sun, but that's where the similarities end. "E" is one of these weird helium-rich stars and this gas also appears to be concentrated in patches caused by rotational and magnetic forces. This kind of stars is still poorly understood and we need to do a lot more study to unravel their mysteries.
Where the orbit of "A" and "B" is stable, those of "C", "D" and "E" are not and soon they'll be flung into deep space, ever further away from the central pair. "A" and "B" on their part are so massive that they'll have a very short lifespan after which they'll both explode. "A" will be the first to go, possibly causing such a shockwave that it'll expel also "B" from the system.
High-accuracy observations have also revealed numerous brown dwarves in this system, stars that are actually too small to become real stars but which still radiate much more energy than they receive from their environment. Their size should be only a couple of times that of Jupiter.
I deliberately made this sketch during a full moon, just to show you what this does to the normally dark background of the field of view. But still, the Sigma Orionis system was a joy to look at. Interesting to note is another triple star in the same field of view, denominated "Struve 761", just a bit below Sigma Orionis (the 3 brighter ones). Again you can see how deceiving an observation can be because this system is actually much closer to us than the Sigma Orionis system, 142 lightyears against 1.150 lightyears!

Tuesday, 15 March 2016

Leo's bearing triplets!

I'm sorry for all of you who believe that Leo's a magnificent male lion because in reality she's a lioness. In fact, a pregnant one too because she's bearing triplets in her belly! What you see on my sketch is a group of three galaxies, about 36 million lightyears away. M66 is the most prominent one (bottom). It's more or less the size of our own galaxy but it's much heavier. That's because at some point in the past (we guess about 800 million years ago) it had a close interaction with NGC3628 (top left), the result of which is that it has an extreme central mass concentration and an unusually long, sweeping spiral arm which is barely visible here. 

NGC3628's also known as the "Hamburger Galaxy". With my binoculars it was again almost impossible to make out, but this galaxy features a very large and prominent dust lane all along its length, making it look like a hamburger squeezed between the two parts of a bun. When viewed through larger instruments this galaxy rather resembles a bone, with large clouds sticking out at both edges. These clouds consist of stars and gas and are also the result of its encounter with M66. Gravitational forces were so strong that they literally tore the galaxy's gas out, leaving the galaxy itself completely deformed. 

M65 (centre right) is the least interesting of the three. Star formation in it seems to be very low and therefore it has a very high ratio of older stars, although a recent burst of new star formation suggests that it may have had  a close interaction with the other two as well. 

Although a pair of binoculars are not the ideal instrument to observe distant galaxies, this trio truly deserved the visit because they were sitting so nicely within the large field of view. And in the end I was happy that I managed to make out more detail than I originally anticipated.

Friday, 11 March 2016

Bigger is better!

There's no field where the above statement is more true than in astronomy. No matter how you cut it or for how long we discuss about image quality, contrast and light-pollutes skies, there simply is no substitute for aperture. In the 35 years that I've been an astronomy enthusiast I've had the privilege of owning or using just about every type of telescope you can imagine, even some very exotic ones like a 25cm f/20 Schiefspiegler built by the extravagant German artist Anton Kutter. But every single time that I've had the opportunity to compare two different instruments of equal build quality, the bigger one always won the contest. So over the years my hunger for more became an unstoppable craving. The desire to see ever better and to penetrate ever deeper into the depths of our universe in order to satisfy my humble curiosity kept throbbing in my chest. I just couldn't help it. I got overwhelmed by an extremely virulent disease we astronomists call "aperture fever". It basically means that you can't stop buying new, and especially bigger, telescopes. Once you're under its spell, there's hardly any cure and the only thing you can do is to give in. So after my very first scope, a small 60mm Vixen refractor which I've held and pushed to the limits for almost 20 years (!), I bought a 20cm (8") Celestron Schmidt-Cassegrain (or more commonly called "SCT"). The 8" SCT was everybody's dream telescope in the 1980's but at the time only accessible to a lucky few, so you can imagine how happy I felt when I realised that I could finally afford one! Only to find out... that over time things had changed a little and that the 8" SCT was no longer the mightiest kid on the block. 

In the 1960's an American amateur astronomer called John Dobson built his first telescope out of plywood, formica, closet flanges and other bits and bobs. Its design was incredibly simple: a classic Newtonian reflector on a home-built mount which allowed you to move the telescope to the left or right and up or down. No complex equatorial mount with gearboxes and motor drive. No aluminium tripods and counterweights. It just looked like a giant soap drum on a wooden crate. But oh boy did it perform! The enormous advantage of the simplified version of old Newton's design was that you got a lot of all-important telescope aperture for very little money. Many amateurs even started grinding their own mirrors with surprising results and by the end of the 1980's a 20cm (8") mirror had become small compared to what many astronomers managed to build in their own garage. It didn't take long before the so-called Dobsonian telescope was commercialised and these days the names of Obsession, Starmaster, Webster and Lukehurst resound stronger in the astronomy world than the classical telescope manufacturing brands such as Meade, Celestron and the like. Moreover, the home-grinded optics of the Dobsonians are usually far superior to those of the large-batch factory telescopes and are probably only exceeded in quality by Nasa.

When I eventually put my 8" SCT next to a friend's completely home-built 35cm (14") Dobsonian, I was in for a shock. Not only did it blow my classic telescope to smithereens optically speaking, my friend had actually paid a lot less for his telescope than I had done for mine! So my SCT quickly ended up for sale because I wanted to see at least as much as what I had seen through that 14". So I got a 14,5" second hand. A wonderful telescope made completely out of carbon fibre, which made it extremely light and incredibly easy to transport to a dark site. But still my hunger wasn't satifsied so two years later I built my own 18" Dobsonian: the notorious PeterDob. But then I ran into another problem. After having spent the first 30 years of my astronomy existence peering through telescopes with one single eye, I got sick and tired of it. I tried to use an eyepatch so I didn't have to squeeze the eye I didn't use all the time, but that didn't help. The ideal solution appeared to be a so-called binoviewer: a set of prisms that split the single light beam of the telescope in two so you can watch with both eyes. Unfortunately, these binoviewers come with a price and I'm not just talking (a lot of) money here. In the end a binoviewer doesn't just split the light beam but also loses a lot of it in the process. Considering that for astronomical observing you need every photon you can get, this was very bad news indeed. On top of that, binoviewers are long and in order to get them to focus you need to attach a corrector lens in front of it which squeezes out even more light and comes with an unwanted extra magnification. Eventually I've owned or tried just about every binoviewer on the market, from the cheap chinese over the top-notch Baaders and Denkmeiers up to the enormous 2" Siebert beast. None of them, however, were able to show me as much as with single-eyed viewing and this was yet another disappointment. 

Now, I've come at a point in my life where I want to buy the telescope of my dreams, an instrument that will keep me happy for the rest of my life and which will not be a compromise of any kind. Of course there are limits and budget isn't the most important one. You can want the biggest telescope in the universe but what good is it if you can't get it in or out of your garage? Worse still, what use is an incredibly big telescope when you're living in a city centre and need to get way out of town to find a decent sky for observing? So in the end, my dream telescope is still a compromise but one that will be difficult to surpass: a 457mm (18") BINO-Dobson! Yes! You've read it correctly! I've ordered a telescope that's essentially two 18" Dobsonians tied together so you can watch with one eye in each! No more nasty binoviewer hassle, increased magnification, light loss and... it comes with another incredible advantage over monocular telescopes with a much bigger mirror: a binoscope delivers the same optical performance as a telescope with 1,4 times its diameter (so my 18" bino will be at least equal to a 25" mono), but you can still use rather low magnifications. I already explained that telescopes have a minimum magnification and that this increases with its aperture. For example, with a 25" mono you can forget looking at the entire Orion Nebula in the same field of view. With my 18" bino on the other hand, this is still perfectly possible. But there is more. Watching with two eyes seriously increases contrast. That's because it's unlikely that a weak but "true" light signal is being discarded by both eyes as "false" at the same time. The result is a darker background and much more contrast on faint objects. According to scientists, a binoscope therefore performs like a telescope even 1,8 times its diameter here! For my 18" that would mean the performance of a 32" without the latter's enormous size, weight, unearthly minimum magnification and having to stand on a ten-foot ladder. 

Critics of this rather new kind of telescopes say that they're incredibly difficult to adjust because the alignment of both tubes must be absolutely perfect. This is true, but nowadays the build quality and technical solutions more than take care of that. Some also argue that a binoscope is exuberantly expensive. That... turned out to be false! Actually I'm paying a lot less now than if I had ordered a classic 25" Dobsonian from a quality manufacturer, let alone a 32". 

Currently, after having waited for almost a year, my dream telescope is almost finished. I can't thank the builder, Mr. Otte, enough for his excellent craftsmanship and patience and hope that it'll arrive at my door soon. There's still a lot of testing to be done but now I'm sure that I've found the perfect telescope for me. And then... I'll keep posting hundreds of sketches here so you can have part of the fun as well. And shouldn't that be enough to satisfy you, Italy isn't all that far away...

Tuesday, 8 March 2016

The Sword of Orion... in colour!

As I already explained in an earlier post, there's so much colour to be seen in the dark, nightly sky, much more than we can possibly imagine. The object just needs to be bright enough to reveal it to our inadequate human eyes. Now it so happens that there's an incredibly bright nebula out there... an object of such rare beauty and complexity that it'll leave you dazzled, even when you're looking at it for the millionth time: the Orion Nebula (also see here). If you've got a sufficiently large telescope, let's say with a diameter of about 8" and up, this nebula will reveal the same greenish-blue hue of the Eskimo Nebula (see here) but possibly even stronger and all across its brighter parts and filaments. You'll remember that this colour indicates a large presence of hydrogen and oxygen in the nebula and per chance this is also the colour we perceive most easily in the dark. 

Red, on the other hand, is the colour which is most difficult to make out, although if you look at photographs from various nebulae it's often the most prominent tone. That's because also red indicates the presence of hydrogen, which evidently is the most abundant element in our universe. But as far as my personal experience goes (limited to the northern hemisphere), apart from stars which are point light sources, no extended or diffuse object has ever been bright enough to reveal red to my eyes. There's one exception however... the mighty Orion Nebula! I made this observation with my good old 18" Dobsonian under not really ideal conditions. I remember that the sky's transparency wasn't all that great and my eyepieces were constantly fogging up due to the humidity in the air. But I did see it! Right along the brightest borders of the nebula I noticed a reddish-orangy hue, contrasting nicely with the blue-green of the rest. I couldn't use a nebula filter to make the nebula stand out more against the background because these filters actually block all frequencies of light apart from blue-green. So many details within the nebula weren't quite as visible as they could have been with the use of a filter. But that would have destroyed the reddish tint on its edges, which after all was the goal of this observation. Yet I was incredibly happy because I'd seen it. 

Observing the night's sky is often a work of patience and allowing yourself to adjust to the image. Take your time and never be too hasty or you may miss some exciting details that only reveal themselves after a couple of minutes. If your observation spot isn't completely immersed in darkness, it'll also help to use a hood of some kind to prevent stray light from entering your eyes. You should only see pitch black around you, apart from the field of view of your instrument. Relax. Sit down comfortably. And then... let it all come to you. It will!


Friday, 4 March 2016

Two jewel boxes for the price of one

In my previous post I talked about the advantages of binoculars over telescopes. Here's an example of a view that would simply be unthinkable through a telescope: these two wonderful star clusters in the same field of view. They haven't got a name as such, or at least that I'm aware of, and are scientifically referred to as M46 (on the left) and M47 (on the right). They're located a bit to the left of the brightest real star in our sky, Sirius, in the obscure constellation of Puppis, the stern of the ship Argo. The differences between the two are striking and loyal readers of my blog will already have guessed that they are completely unrelated to one another. M47 is fairly young (78 million years est.), not too rich and its stars are still very bright and hot. M46 on the other hand is much more mature (300 million years est.) but also much richer with an estimated 500 members. The image also completely fools us because M47's actually much closer to us: 1.600 lightyears against 5.400. But here on Earth we see them very close to one another. Not quite close enough to admire them as a couple through a telescope, however. As I explained, telescopes magnify more and will never allow you to observe these two in the same field of view and at the high level of brightness of a good pair of binoculars. 

The image also hides a little surprise for keen observers. Dim the lights, relax and concentrate as if you were truly looking through a telescope. Focus on M46... towards the top of the cluster... (I'll leave you for a moment with this sketch and continue writing under the image)

Have you seen that tiny little faint patch? It's a planetary nebula! And... no, it has nothing to do with the cluster itself as it lies more than 2.000 lightyears closer to us. High-resolution photographs reveal that it has a very faint but large outer halo whereas the visible part marks the death of the red giant star in its centre. All that is left of the star is a small white dwarf which is in fact one of the hottest stars we know. It has a surface temperature of 75.000°C, compared to 5.500°C on the surface of our Sun! Next time we'll zoom in a little bit, so keep following this blog!

Thursday, 3 March 2016

Binoculars and a very wild duck

Isn't it about time you take your binoculars that've been collecting dust for years out of the closet? It's really a shame you haven't used them more often! In general, people believe that you need a real telescope, and a very big one too, in order to see something interesting in the night's sky. This couldn't be further from the truth! Ordinary field binoculars, the one you've used on the odd occasion for spotting birds or spying at your neighbour when he was building that new shack, are just the perfect tool to explore the heavens and especially so if you haven't got a lot of experience yet and you're still hesitating to spend a lot of money on a telescope. Not only do they have more light gathering power than an entry-level telescope (!), which is so incredibly important as I shall explain hereafter, but they also use low magnifications and therefore make it easy to scan the sky and find various objects. Take a look at the numbers that are probably written on its back. Chances are that it's a "7x50" or similar, which indicates that its magnification is 7 times and that its lenses have a diameter of 50mm. 

Now what does all of this mean? Contrary to popular belief, the most important job of a telescope is not to magnify but... to capture light. Much more than we humans can with our teeny-weeny eyes and then concentrate it so that it all fits into our pupil. So you have to see the lens or primary mirror of a telescope as its "eye" as this will be an indication of how much more a certain telescope will make you see. Suppose that the fully dilated human pupil has a diameter of 7mm. Then an entry-level refrator (or lens telescope) with a diameter of 60mm will capture 73 times more light because the surface of its lens is 73 times bigger than the surface of our pupil. Or in other words, objects appear 73 times as bright as they do with the naked eye. With an 8" (200mm) telescope, the light gathering power increases to 816 times the human eye and my 18" (457mm) telescope is 4.262 times as powerful! However, you shouldn't get overexcited because we're talking zero magnification here. Binoculars and telescopes magnify and the bigger the telescope, the bigger the minimum magnification will be. I'm not going to bother you with the technical explanation of all of this, but suffice to say that if a telescope magnifies 40 times, the light it captures is also spread over a surface 40 times as large. So if we take our 60mm entry-level telescope, at 40x it will show you the object much larger than with the naked eye, but not even twice as bright anymore. An 18" telescope at 80x on the other hand, will still show you the object 53 times as bright as with the naked eye. So in the end, the most important thing you're looking for in a telescope is aperture. We can discuss the technicalities of different telescope designs for hours or even weeks but in the end there's just no match for size. 

But let's go back to our ordinary 7x50 binoculars. Yes, their aperture's only 50mm, smaller than the entry-level telescope of my example. But... they've got two lenses so their light gathering power actually doubles, without even mentioning the effect of observing with two eyes instead of one (binocular summation factor). What's more, because of their very low magnification the image remains extraordinarily bright, which is an absolute bonus when you're trying to observe very large but faint objects such as the With Head nebula. Now do you understand why all serious astronomers will never let go of a good pair of binoculars, even when they've got a telescope the size of a house?

Take a look at my sketch. The object is M11, or for some reason that is totally beyond me nicknamed the Wild Duck cluster. It's an object you can't miss in the summer sky, in the small constellation of Scutum (the Shield), just below Aquila (the Eagle). With its 2.900 stars it's one the most compact and richest clusters in our galaxy and perhaps it does deserve to be magnified a little more through a telescope. But look how brightly and elegantly it appears in the large field of view of my binoculars! Every single star can still be resolved like the grains of a small heap of salt that someone accidentally spilled on the table. And that, dear readers, is poetry, isn't it? :-)


Tuesday, 1 March 2016

There's an Eskimo in Gemini

I'm sorry, my dear Inuit friends, if the title of my message sounds a bit derogatory but I wasn't the one who invented the name of the object I'd like to talk about today. Irony aside, it does look a bit like a head surrounded by a parka hood, doesn't it (here seen lying down)? I already explained what planetary nebulae are in my message about the Crystal Ball and that's exactly what the Eskimo Nebula, or scientifically denominated NGC2392, is. The star inside of it was once very much like our own sun in terms of size and overall aspect but unfortunately it has reached the end of its life. Nuclear fusion became unstable and its atmosphere's blowing away into space. Already with a reasonably small telescope it's possible to distinguish the two main gas shells which give the Eskimo its peculiar shape. Very large telescopes reveal that the outer shell consists of unusual lightyear-long filaments, like sunrays around the star. The inner shell's also much more complex than what my home-built telescope could make me see and in reality looks a bit like a ball of twine or a sort of bubbly fishnet structure around the dying star. We estimate that the star began to fall apart some 10.000 years ago, so more or less around the time when humans started to abandon their roaming hunter existence and became settlers. When thinking in stellar terms, wouldn't you say that this nebula developed itself pretty quickly? The gas is expelled at a speed of a whopping 300.000 kilometres per hour and will eventually dissipate into space, while the star will cool down and extinguish.

Another interesting quality of planetary nebulae is that they usually have a very high surface brightness. They're often bright enough to show colour when observed through a telescope! In general our eyes are able to make out a blue-greenish hue in most of these small but bright objects, which corresponds to the presence of hydrogen (greenish) and oxygen (blue) in the nebula. It so happens that blue is also the colour to which our eyes are most sensitive in the dark. Let's just say that we're in luck! 

The sketch itself is already a couple of years old and it's not one of my best, according to my opinion. But this nebula's one of the easiest and brightest in the sky and definitely one of winter's favourites, so I couldn't just skip it.