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!