Wednesday, 30 November 2016

Flying over the Moon...

I hate sketching the Moon. The reason for it is that it's too darn complicated. When you point any telescope at the Moon, be it a supermarket model or the biggest and most expensive gun on the market, be it at low or high magnification, you get so overwhelmed by the millions of details that it's easy to lose courage. Most Moon sketchers therefore stick to one or two craters at the time, even though there's so much more to see in the telescope's view. But unfortunately I can't do that. I always try to represent as accurately as possible what it was that I saw through my telescope and therefore it's such a pity to sketch only a detail and leave out all the rest. 

But a couple of weeks ago I got all of my determination and patience together and spent 3 hours behind the telescope to produce this sketch. Plus the bigger part of the following weeks to work it all out on the PC until I felt reasonably satisfied. There are still a couple of errors on it and some things still don't seem exactly right to me, but one day you just have to let go and publish. So here it is. I hope that you enjoy it.

The subject of my sketch is the area near the famous Ptolemaeus crater (bottom). With a diameter of 153km it's a very big one. The lava-flooded floor's surrounded by walls up to 2.900m high and is scattered with tiny impact craters, two of which were easily visible. To the south (up on my drawing) lies the slightly younger Alphonsus crater. It still features this typical central peak and its debris-covered surface is cut by a network of rilles. Further north (top of the sketch) lies Arzachel, relatively young and intact. Its prominent central peak rises 1.500m above the crater floor and its sharp wall are up to 3.600m high! These craters form the eastern border of Mare Nubium, the southern sea of clouds, which at the time of sketching was still awaiting dawn. On the right lies the ancient Albategnius crater with its eroded and heavily bombarded cliffs, which surprisingly still rise up to 4.000m above the crater's floor. 


Monday, 21 November 2016

It happened on the 4th of July 1054

No, not Independence Day! The Vikings had only just arrived in Newfoundland, let alone Columbus or Mayflower settlers. On this particular day chinese astronomers recorded the appearance of an unusually bright star in the sky. It was five times brighter than Venus and remained clearly visible even during daylight for 23 days. It then continued to remain visible to the naked eye at night for another two years. The carefully compiled chinese records are confirmed by later Japanese and Arab documents and it was also portrayed by the Pueblos and Mayas and accounts of it are still being told in Aboriginal legends. 

Strangely enough, no trace of this mysterious new star can be found in contemporary European literature, apart from some unreliable sources dated many centuries later. However, we have to consider that Europe was going through a period of disaster. Edward the Confessor's reign over England was weakened by internal struggles and local barons incessantly conspired to seize more power. Holy Roman emperor Henry III was constantly on the war path against the Hungarians, Flemings and Poles, neglecting his German homeland that lay in ruin. The Normans conducted violent raids against Byzantium. Only months earlier Pope Leo IX had excommunicated the Patriarch of Constantinople, bringing about the great schism between the Catholic and Orthodox churces, and had died soon afterwards, leaving also Rome in turmoil. 

The most likely reason why it wasn't mentioned is that many people in Europe must've believed that the star announced the end of the world. In the early Middle Ages it was generally thought that the universe had been created to last for 6.000 years (1.000 for every day of creation), 5.000 of which had already passed by the time Jesus was born. So anyone living in Europe around the year 1.000 would not have felt very much at ease and the sudden appearance of that new star must've struck many people with terrible fear.

But two years later the star had gone, seemingly without leaving a trace, and business in Europe and the rest of the world was still as usual. It was not until 1921 that scientists lay the connection between a strange nebula, discovered in 1731, and the events described in the chinese chronicles. This nebula, M1 or popularly nicknamed the Crab Nebula, happens to be the home of the strongest X-ray source that we observe in our sky: the Crab Nebula's pulsating radio star, or pulsar. It is what remains of a star so violently compressed by a supernova explosion that it's become a tiny but heavy ball of neutrons that rotates at a very high speed. Pulsars have an extremely powerful magnetic field and emit radiation in a beam not necessarily aligned with their rotation axis. This means that we observe regular radiation "pulses" that come from those stars according to their rotation speed. To put it simple, they're oversized lighthouses. In the case of our Crab Pulsar, the lighthouse shines in our direction 30,2 times per second. Now that's fast, isn't it? The nebula which hides the pulsar to visual observers is all the rest of our exploded giant star and over time scientists have been able to measure a significant increase in size. Not surprising since the supernova blast expelled the star's atmosphere at an incredible 20.000km per second (!) and even today it keeps expanding at 1.400km/s. Given time, the still fairly young and compact Crab Nebula will be ripped apart and dissipate into space, just like the Veil Nebula which is a remnant of a supernova that happened some 5.000 years earlier and of which only delicate filaments of gas can still be observed. Considering its respectable distance of more than 6.000 lightyears, the Crab Nebula is still one of the brightest planetary nebulae in the sky. Imagine what an explosion it must have been!

Wednesday, 16 November 2016

Has anyone ever seen a black hole?

The answer is yes. Actually, there are black holes out there that anyone can see and you don't even need a gigantic telescope for it. Surprising, isn't it? Aren't black holes supposed to swallow all matter that comes too close and aren't they supposed to be so massive that even light can't escape from them? Yes, of course, but the interesting bit happens just before the matter disappears in the apparently bottomless, black void. 

Imagine this incredible black hole, a sort of cosmic whirlpool that attracts anything unfortunate enough to come too close. Entire stars are being ripped apart by its unequalled gravitational pull and form dense clouds of matter around the hole before being absorbed. Pressure increases up to a point that the highly compressed gas begins to emit vast quantities of radiation in all frequencies of the electromagnetic spectrum, also in visible light; radiation that only just manages to escape from the boundaries of the black hole. So if we want to find a black hole, you don't have to look for a black spot in space but for an unusually bright spot! A spot so bright that, even though perhaps only a thousand lightyears across, it emits so much light and other radiation as an entire galaxy! 

Now have a look at my sketch. The object in question is M77, a very large barred-spiral galaxy, nearly twice the diameter of our Milky Way. You can clearly see its spiral structure and the bar-like structure at its centre's more than obvious. I was also thrilled to be able to make out the extremely faint halo that surrounds it and which also consists of many billions of stars. But the most interesting part is its core. Look how small and bright it is! It alsmost looked stellar through my telescope! This is what scientists call an Active Galactic Nucleus;  an extremely compact core because of the accretion of vast quantities of matter by the supermassive black hole at its centre, which possibly contains a mass of 15 million suns. These "AGNs" are the most luminous objects in the entire universe and this particular one's probably the closest to Earth, being at a distance of merely 47 million lightyears. These days scientists believe that every galaxy has a black hole in its core which acts like the gravitational engine that makes it swirl, grow, create stars and hence create life. But this one must definitely be one of the biggest in our backyard. Get your telescope out and have a look at it too!


Friday, 11 November 2016

Taking a spaceship deep into the Orion Nebula

I've already posted about the bewildering Orion Nebula (M42) here and here. So far we've remained at a respectable distance. Now buckle up because I'm going to take you on a wild roller coaster ride deep into the heart of the nebula. 

It's a beautiful night with a highly transparent mountain sky. My 18" binoscope's set. Magnification's 507x. Put your eyes against the widefield lenses. You feel as if you're falling into them... ever deeper... breakneck speed... you're dazzled... all around you are bluish clouds of hot gas... filaments that are reaching out at you... an amazing sensation of depth overwhelms you... stars lie embedded everywhere in the nebula and shine like street lights through the mist... so many bright little spots... so many newborn suns, nurtured by the giant cloud until they're old enough to be expelled and start their journey through space... every single one of them will probably form planets, dreams of the future in this currently violent and deadly corner of our universe... the radiation from all of these young and hot stars is scorching... hydrogen and oxygen reach high states of excitation and glow in the absolute dark... they glow so much that at a distance of 1.300 lightyears this cloud can still be seen quite easily with the naked eye... lanes of dark dust are drifting by, absorbing light as in an autumn sunset...

And there are you, a tiny little person, an insignificant insect in the middle of this nebula that's 24 lightyears across. You could send a text message from one end to the other and you'd only get a reply 48 years later! Still, some people believe that they're the most important part of this universe. Astronomy would be the best cure for them.

Wednesday, 9 November 2016

One peanut for the price of two

When William Herschel discovered this planetary nebula back in 1785, he saw two separate lobes and believed them to be two separate objects that were so close that they seemed to run into one another. That's why a century or so later this nebula received two different ID numbers: NGC2371 and NGC2372. But today of course we know that it's just one single planetary that's arrived at the point where it starts breaking up. 

The thin shells of hot gas, remnants of the dying star's atmosphere, have been blown so far away - 1,3 lightyears to be precise - that they are splitting in two half spheres before disintegrating further. The central star has reached its maximum temperature of 118.000°C and will soon start to fade. Difficult to see through the telescope were the two "ansae", plumes of gas that  blew out of the star's polar regions where the atmosphere's less thick and that now form ethereal "clouds" at the astonishing distance of 3 lightyears from the central star (above and below on my sketch). Remember that the nearest star to Earth lies at a distance of 4,25 lightyears so you get a good idea of how far these ansae have wandered off from their origin. It's interesting to compare them to the ansae of the much younger and more active Saturn Nebula, which are clearly still plumes that are escaping from the polar chimneys. It's a bit like the smoke from a steam train that blows out in a puff and when the pressure's released leaves a dark cloud in the sky that quickly evaporates. In the case of our "Peanut Nebula", the clouds are almost gone. 

I absolutely had to share this object with you because it's an often neglected gem in the winter constellation of Gemini. With the nearby and famous Eskimo Nebula which attracts most of the spotlights, the little and somewhat obscure Peanut hardly receives any attention. Shame on us astronomers!