Thursday, 11 August 2016

The eagle's glowing eye

There are so many planetary nebulae out there that sketching all of them would be close to impossible. As you know, they're dying stars that've just shed their atmosphere into space. When I use the term "just", we're talking about only several thousands of years ago, which is a nanosecond compared to the age of the universe. Their incredibly hot core heats up the resulting gas cloud up to the point that it starts to emit light on its own. Slowly this cloud of gas will expand and dissolve into space whereas the core, the remaining white dwarf star, will cool down and eventually extinguish. 

Planetary nebulae are called this way because they truly look a bit like a planet, with their generally round shape. But if you zoom into them, they'll reveal a surprising amount of detail. Gas filaments, structures and different layers give every single planetary nebula a character of its own and make every new one that you observe also a new experience. Yesterday I showed you the "Blue Flash" nebula. Not that far from it you can find this little fellow: the "Glowing Eye" in the tail of the constellation of Aquila, the eagle. With its magnitude of 11,9 it's within reach of most telescopes but due to its tiny size it can be quite tricky to find. For my sketch I used a magnification of 507x, which brought out quite some detail. I could easily see the brighter rim and some filaments of the inner sphere, which does look a bit like an iris. Its central star was also a lot more prominent than the one of NGC6905. 

The distance of this little gem is estimated at 6.500 lightyears...   

Wednesday, 10 August 2016

The Blue Flash

NGC6905 is a wonderful planetary nebula in the small but remarkable constellation of Delphinus. Loyal readers of my blog will already have guessed that this nebula is what's left of a dying normal-sized star. The star's nucleus still survives and has turned into an extremely hot white dwarf star with a surface temperature around 150.000°C. In comparison, the temperature on our Sun's surface is only 5.500°C. A white dwarf's a very peculiar kind of star because its size is comparable to that of the Earth whereas its mass is not much different to our Sun's. Needless to say that it's extremely dense and "heavy". Unlike a normal star, no nuclear fusion takes place in it anymore; it's light and energy emission being solely the result of the remaining heat of what was once an active nuclear fusion reactor. With time, this star will therefore slowly cool down and fade until all that's left is a ball of mainly carbon. This cooling process takes a lot of time, many billions of years, and therefore there aren't such carbon balls or "black dwarves" around yet because the universe simply isn't old enough. 

This particular white dwarf was clearly visible in my binoscope. But perhaps more interesting for visual astronomers, the star's atmosphere was expelled into space and now forms a rapidly expanding bubble of gas filaments around the white dwarf. Also these filaments were more than evident in the binoscope at a magnification of 285x. Actually, I was amazed at the amount of detail that I was able to make out. This planetary also has two extremely faint "wings" just above and below the main nebula on this sketch. These were difficult to see and I've tried to represent just that. Some people therefore call it a mini-Dumbbell nebula because it does look a bit like a smaller and fainter version of the famous nebula in Vulpecula. 

The "Blue Flash" however lies a lot further away from us: 7.500 lightyears compared to 1.300 for the Dumbbell. But I hope that my sketch will encourage you to visit this fainter and more distant planetary as well because it really deserves it.   

Wednesday, 3 August 2016

A veil in summer sky

I've already talked about supernovae before, cataclisms that mark the death of a giant star. Nuclear fusion becomes unstable... the star collapses under its own gravity which in turn causes the violent expulsion of the entire star's atmosphere in a matter of seconds. The acute energy release may be as high as 1044 Joules or the entire energy output of the Sun during its whole 10-billion year life! The expelled matter may reach velocities up to 30.000km/s or one tenth of the speed of light! 

But as dramatic and spectacular as they appear, the remains of the star fade quickly and after a couple of months all that's left is an incredibly dense core that consist of neutrons. Although perhaps only 10km in diameter,the neutron star's density is 1015 higher than that of normal matter and hence it's incredibly heavy. In some cases it may be heavy enough to continue to collapse under its own gravity until it has become a point. At which stage it becomes a black hole: an object with such a high mass that you'd need to travel faster than light in order to escape from it. That's why we can't observe anything within them because nothing, not even light, travels fast enough to escape. 

But supernovae are not just the end. The blast is so strong that heavier elements such as metals are formed and expelled into the universe. So in a sense a supernova feeds the universe with a lot of complex elements which one day may be needed for the creation of planets and... life. And not all's destroyed instantly. Almost 6.000 years ago a vehement supernova lit up 1.400 lightyears from us in the constellation of Cygnus. As far as I'm aware no observation reports from that day exist so we can only speculate how our ancient ancestors stared at the sky in awe when an insignificant star suddenly became brighter than the full Moon. Now, thousands of years later, the remains of that explosion are still visible in a small to medium telescope: the Veil nebula. What I've sketched here is just a part of the eastern region. The total Veil nebula complex is 110 lightyears in diameter, or in our sky this equals 6 full moons, and continues to expand at a breathtaking rate. Gas filaments that mainly consist of oxygen are heated up and ionised by the blastwave of the supernova explosion and start to emit light themselves. Exactly these frail filaments are what makes this nebula so jaw-droppingly lovely to look at and in a big instrument such as my binoscope the spectacle surpasses even the wildest imagination. I just had to share this with you and I sincerely hope that you enjoy it.

How to make astronomical sketches - Part 2

Earlier than planned, I'm releasing the second part of my video series about astronomical sketching techniques. In this episode I'm focusing on the sketching of the background stars, something which is often overlooked but which highly contributes to the overall result. 

Sketching stars is not just putting dots on paper. In order to make the drawing as accurate as possible you need to master an easy technique which I demonstrate in the video. 

I sincerely hope that you enjoy it!

Wednesday, 27 July 2016

How to make astronomical sketches

Astronomical sketching is becoming ever more popular, and with good reason too. Not only is it great fun and does it give additional value to the extraordinary hobby that astronomy is, it's also the best way to learn how to observe. Astronomical objects are usually faint or have details that can only be discerned through a good adaptation to darkness, patience and experience. When you're sketching such an object, you're forced to concentrate on the image but yet relaxed enough to let the details leap out at you. My astronomy teacher 35 years ago therefore told me that in order to learn how to observe one should start sketching. And so I did and I'm still extremely happy for the advice that he gave me as a kid. 

In order to give everyone a hand at sketching, I'm creating a series of videos in which I'll reveal all of my little secrets. Of course, They'll only contain my personal techniques whereas there are just as many techniques as there are sketchers. But nevertheless I hope that my videos will be useful to everyone and I sincerely hope that you'll enjoy them.

Here's the first about preparation. I'm afraid that the second will only follow in September due to... holidays. :-) But I'll keep you informed through my blog whenever a new video's released.

Happy viewing!

Friday, 22 July 2016

Saturn, the extraordinary planet

Ever since Galileo pointed his little telescope to Saturn, the 6th planet of our Solar System has always been observed with marvel and wonder due to its extensive ring system. Saturn's not the only planet with rings. The first probes that were sent to the outer Solar Sytem in the seventies, discovered that also Jupiter, Uranus and Neptune have a number of rings, albeit not nearly as big and spectacular as Saturn's of course. The ring system looks very impressive and is indeed 282.000km across. However, at most places it's only 30ft thick (!) apart from a few areas where the thickness increases to a few kilometres. If Saturn were a ball with a diameter of 1m, the rings would actually be 10.000 times thinner than a razor blade! Their origin is still uncertain and the most prominent theories suggest that they are the remains of a former moon that got too close to the giant planet and was ripped apart by tidal forces, or that it's just debris left over from the time that the planet was formed. They consist of water ice particles, with some traces of rocky elements, ranging from 1cm to 10m in size. Next year the rings are at their most visible because they'll be completely slanted towards us, and so they already show well on the sketch that I've made. But since Saturn's tilted, just like Earth, the angle at which we see the rings changes over a 28-year period (the time it takes Saturn to orbit the Sun). In 2009 we saw the rings edge-on and as such they were difficult to see, a phenomenon which will happen again in 2025. The ring system is extremely complex with different densities and even gaps. The most famous "gap" is the Cassini Division, which you can see clearly on the sketch and is easily visible already with a small telescope. It's not really a gap but just a region of lesser density, some 4.800km wide. The Encke Division, nearer to the edge, was hardly visible during this observation due to the extremely poor conditions. It's a 325km gap caused by a tiny moon, Pan, that orbits within it! 

Saturn itself is the second-largest planet of our Solar System, with a diameter roughly nine times that of Earth. Though it's mainly composed of gas, for the largest part hydrogen and helium, and hence its density's a lot less, resulting in a mass about 95 times that of our planet. Ammonia crystals in its upper atmosphere are responsible for the pale yellow hue. Wind speeds can reach 1.800km/h, which is much faster than the speed of sound and even faster than the hurricanes on Jupiter, but not as fast as the winds on Neptune. 

No less than 62 moons have been identified, excluding the hundreds of moonlets that hide within the rings. Titan, the largest of which, can also easily be spotted with a small telescope or binoculars and is seen here on the far right. It is the second largest moon in our Solar System, after Jupiter's Ganymede and it's even much bigger than Mercury (sorry, Astrologists), though not as massive. What's more interesting, Titan's the only moon known to have a dense atmosphere and it's the only place apart from Earth where stable bodies of surface liquid have been found, albeit liquid methane and ethane instead of water. But Titan's methane cycle is very similar to the water cycle on Earth and also its general aspect is thought to be the same, with oceans, dunes, rivers and mountains. Unfortunately, its thick and cloudy nitrogen atmosphere (denser than Earth's!) prevents the surface from being examined visually so we had to use infrared and radar to discover it. Given the presence of many complex molecules and the conditions similar to those on primordial Earth, many scientists have highlighted Titan as a candidate for extraterrestrial life. Although there are many obstacles such as the extremely cold surface temperature of -179°C and the absence of CO2. In 2004 a simple probe was sent down to its surface which transmitted a lot of interesting readings back to Earth. Scientists hope to send a more powerful probe to Titan within the next decade.

In total I could see 5 moons, less than I could expect with my new 18" binoscope, but as I already mentioned, the conditions were terrible. I was actually doing a test run of the telescope and still had to complete a lot of work on the correct alignment of the two telescope tubes. Therefore I chose to observe from an illuminated car park with an asphalt surface after a very hot day. Probably the worst place one could choose for astronomical observing because asphalt absorbs a lot of heat and re-emits it during the night, causing a lot of horrible heat turbulences. But now the telescope's finally ready for use and I can't wait to take it up in the mountains. Be ready for more sketches soon! 

Tuesday, 19 July 2016

The power of star formation

While I'm still adjusting my new binoscope, I'd like to present an older sketch but with a very interesting subject. The faint little patch you see here in the drawing's centre is a nebula denominated NGC6857. It's an emission nebula, which means that it doesn't just reflect the light of the surrounding stars but that it's heated up so much that it begins to emit light on its own. This particular nebula is part of another gigantic star forming region in our galaxy but much further away from us than for instance the Orion nebula complex. The distance of NGC6857 is estimated at 25.000 lightyears, which is at almost one quarter of the total diameter of our galaxy. The sketch was made with my good old 18" Dobsonian telescope so you can guess that it's not a particularly easy object and as such reserved for larger telescopes. You can find it in the heart of the constellation of Cygnus, near the rim of the Great Rift, a large, dark cloud of dust that can easily be seen with the naked eye (under a dark sky) and which seems to cut the Milky Way horizontally in two. As I mention it, some darker patches were also visible in the telescope view as I've reflected in the sketch. You have to imagine that the brighter background glow is caused by millions of stars that are so far away that they can't be resolved through an amateur telescope. The darker patches are clouds of dust that block the light from the stars behind them. 

Returning to our nebula, the odd thing about it is that it's also a very powerful maser; one of several in the area. A maser is quite similar to a laser, but emitting a beam of microwaves instead of light. Surprisingly, the most common molecules responsible for this are water and methanol, apart from other OH radicals and silicon monoxide. Radiation in the hot star forming cloud excites these molecules up to a point that the majority of them turns into a higher energy state. In turn they start to amplify microwave emissions which are by far the strongest emissions that we observe in the entire radio spectrum. Sometimes listening to our universe can be more exciting than looking at it!