Friday, 10 August 2018

IC4954/5: Shedding the birth veil

Some six degrees north of the famous Dumbbell Nebula, at the border between the constellations of Vulpecula and Cygnus, dwells a small star cluster. Roslund 4 is not all that difficult to observe, in spite of its considerable distance of 6,000 light-years, and should already be visible through a three-inch telescope given good sky conditions. 

A bigger challenge is the surrounding nebulosity (IC4954 - IC4955) which reflects the light of the stars in this cluster, born out of it hardly 4 million years ago. The young, hot stars have fired up nuclear fusion at full power and the ensuing radiation, up to 3,000 times solar, is currently blasting the nebula away. The sharp edge where the stellar wind's hitting the nebula actually serves as a very convenient yard stick with which we can measure the expansion speed of the nebula. It is estimated that within the next 6 million years the nebula, still containing about 60 solar masses of matter, will have dissolved completely. 

Thursday, 9 August 2018

Mars

The red planet has fascinated mankind since the dawn of civilisation due to its remarkable colour, even when viewed with the naked eye. Therefore it was linked to the ancient gods of war and even today astrologists still attribute strong animal instincts to it such as anger, lust and energy. 

Of course, this is all nonsense.

Mars's reddish colour derives from the significant iron content of the dust on its surface, which in a very distant past reacted with oxygen. So it would be correct to say that Mars is... rusted. 

For astronomy enthusiasts on Earth, Mars is not an easy planet to observe because the faint details on its surface drown in its significant brightness. It's like looking at a seriously overexposed photograph. Fortunately, looking with both eyes in stead of one reduces this effect and I didn't have a lot of difficulties distinguishing the surprising details you can see on my sketch.



Monday, 6 August 2018

Lunar eclipse

A lunar eclipse is always a wonderful event and there's little that I can add to what other, more talented bloggers and writers have said about last month's "blood Moon". Suffice to show you my impression of how my wife and I observed it through my Nexus 100 binoculars at 24x, just when the Moon was about to leave the Earth's shadow...



Here's the original sketch:

 

Friday, 27 July 2018

Berkeley 81: Into the mist of our galaxy

Here we go again... Once more a sketch that'll rank high on the least-popular list because, let's be honest, it almost looks like a blank sheet, apart from a couple of small stray stars. Yes, I know that this won't be the easiest or most spectacular sketch and that Blogger doesn't allow you to open the image real size, but please give it a try. 

No, don't look at the sort of framework of brighter stars that seem to form two parallel lines from top to bottom because they lie a lot closer to us than the object I'm trying to tell you about here. Look at the two stars at the centre and then just below them. Look very carefully; turn off the lights if you have to. Don't you see a small group of incredibly faint stars appearing? I've tried to represent them just as faint as they were for me at the telescope and also I had to glance for a bit before these stars suddenly revealed themselves in the dark grey mist. 

Berkeley 81 is a remote cluster that lies 10,000 light-years away in the direction of our Milky Way's core. With all the dense clouds of dust and gas in the area, it's not surprising that this cluster appears so faint because a lot of its light's being absorbed. It's like looking at a distant light on a foggy night. The cluster's intriguing because of its position and its high age, estimated between 750 million and 1 billion years. Usually galactic star clusters get torn apart quite soon by our Milky Way's gravity, especially when they're so close to the core. Yet, this one's still resisting. Perhaps because it's lying somewhat above the plane of our galaxy? Or because it's not an insignificant cluster, containing about 1,500 solar masses? 

Oh, how I just love these off the beaten track objects... :-)


Thursday, 26 July 2018

NGC7026: The cheeseburger

Some 5,700 light-years away in the constellation of Cygnus, the swan, lies this small but highly interesting planetary nebula. At first glance you'll notice its two bright equatorial lobes and the sort of dark lane that runs across it, effectively giving it the appearance of a cheeseburger. 

The progenitor of this nebula is a very hot (80.000°C) white dwarf star in its centre, which was invisible to me at the telescope. This central star was once a star very much like our own Sun, with an estimated mass of 1.1 times solar. Having finished its hydrogen supply long ago and with helium fusion becoming unstable, the star blew off its entire atmosphere merely 1,500 years ago. Since the atmosphere's much thicker at the equator due to centrifugal forces, the gas can't escape as quickly there and builds up in these bright lobes, expanding at 50 km/s. At the poles, on the other hand, the gas blasts away much more easily and reaches speeds of 150 km/s, hence creating the somewhat cylindrical-shaped nebula. Beyond the polar gaps we see several emission knots which are in fact high speed parcels of gas related to the early stage of the nebula's formation and which are flung out at over 180 km/s. 

Scientists theorise that this nebula developed very fast, producing violent shockwaves and instabilities to its environment, unlike more common spherical-shaped planetaries. In a sense this nebula's quite similar to the older and better-known Butterfly (M76) which also exhibits a turbulent, bi-polar structure. Without any doubt the Cheeseburger will eventually evolve along the same lines before disappearing forever within the next ten to fifteen thousand years.


Tuesday, 24 July 2018

NGC7008: Evidence of extrasolar planets

Every planetary nebula, the remnant of a small to medium-sized star, is unique. Just browse through all of my sketches and I'm sure that you'll agree. They all tell a different story and even reveal a lot about the nature of the star system that eventually got destroyed when the central star exhaled its dying breath. 

NGC7008, nicknamed the "Fetus Nebula", is one of my all-time favourites. Just look at its highly irregular structure, which is already obvious through a small telescope. After zooming in with the binoscope I had to pick up my jaw from the ground because I'd never seen anything like this before... and believe me, I've seen quite a few planetaries in my 36 years of being an astronomy enthusiast.

On either side of the central star there are bright patches of nebulosity. Remember the FLIERs I told you about when discussing NGC6826? These are exactly the same but much older and more developed. But obviously there's more... much more. Usually planetary nebulae form a spherical or ellipsoid sort of bubble. Here, the bubble's irregular and even appears ruptured. 

Scientists speculated that the big central star was in fact a binary and that the interaction with this companion disrupted the nebula's formation. More recent observations with the Hubble space telescope revealed dual layers of completely different content in them. Moreover, these layers appear near the edge of the nebula, where it meets the interstellar medium. This makes a companion star highly unlikely. A new theory suggests that the expanding nebula's interacting with planetary debris... bits and bobs of planets that were destroyed during the expulsion of the central star's atmosphere. This would account for the inhomogeneities in the nebula and, if massive enough, rings of matter would be formed that generate the sort of structures we see here when stellar gas crashes into them.

In short, it seems that this odd-looking nebula is providing us with key evidence that once a complex planetary system existed around the central star. 


 

Monday, 23 July 2018

NGC6826: The blinking planetary

Visual astronomy is a very subjective matter because the human brain can easily be fooled. I'll be the first to state that my sketches are merely an impression of things that I think I've seen, without claiming any true scientific value. 

A popular example of such optical illusions is this bright planetary nebula in Cygnus, which bears the nickname "Blinking Planetary". The reason for this is that many people report that it seems to fade and reappear very quickly, as if someone's playing games with a light switch. Obviously this is wrong as planetary nebulae generally do not change brightness overnight, let alone in a matter of seconds. The illusion's caused by its very bright central star. When focusing on it with your eye, the surrounding - much fainter - nebula seems to disappear somewhat. When you then turn your gaze away from the star, the nebula reappears. No magic, just our eyes having difficulties adapting to different brightnesses when already observing under unusual (very dark) circumstances.  

What's more interesting though, are the bright patches at the nebula's border, on either side of the central star. Scientists call them "FLIERs" (Fast Low-Ionisation Emission Regions), the origins of which are still not well understood. One theory goes that they're gas that was hurled out from the star about a thousand years ago at supersonic speed, but in that case their bow-shock points in the wrong direction. Another theory suggests that these patches of gas are stationary and that the expanding gas bubble scrapes past them.