Tuesday, 20 February 2018

IC418: The Spirograph

There's so much unknown beauty up there that it never ceases to amaze me. In the dark constellation of Lepus, the hare, at the feet of mighty Orion, you'll find this little bugger. It's obviously a planetary nebula, and one that listens to the denominator IC418, but more commonly known as the Spirograph Nebula. It's nick refers to its complex, almost mathematical structure. 

Experts among you will already have guessed that this nebula's still quite young, hardly 2,600 years old, and in full expansion. Though very small in spite of its relatively close distance of 3,600 light-years, you'll quickly notice some extraordinary details if conditions allow you to push telescope power. Its bright outer shell, gas that was expelled when the star was still in its red giant phase, shines brightly under the heat of the brilliant white dwarf in its heart. The inner shell, on the other hand, appeared much brighter still and seemed to sparkle in the atmospheric turbulences of our Earth. This inner shell is the dying star's atmosphere that was blown away into space after nuclear fusion had become critically unstable. Soon the inner shell will expand so quickly that it'll catch up with the much slower outer envelope, possibly even break through it in order to form ansae, like the ones of the Saturn Nebula

So keep your eye on this one because it still has a lot in store for us in the near future... er... in the next couple of thousand years. 

Thursday, 15 February 2018

Berkeley 21: The edge of our galaxy

Loyal readers of my blog know that I'm obsessed with faint fuzzies... objects so difficult to see that you sometimes wonder whether what you see is real or whether you've entered the realm of science fiction. But perhaps the objects that fascinate me more than anything else are extremely remote (and therefore faint) open clusters. Last year already I took you to Berkeley 19, a cluster that lies even beyond the outermost spiral arm of our galaxy. Today, I'd like to take you just a little bit closer, to a distance of merely 16,000 light-years, right in the heart of this outermost spiral arm. There lies this old star cluster, denominated Berkeley 21, the light of which is nearly completely extinguished by the interstellar dust of the broad Perseus spiral arm which lies between the outer arm and our own. In other words, prepare for something very difficult to see. 

At 104x, I only got a hunch of a fuzzy patch... the suspicion that I had nailed it. It was not until I pushed telescope power to 285x that the cluster revealed itself and at 507x most of its stars could be resolved, albeit with great difficulty. For your information, the brighter stars you see on my sketch all lie a lot closer to us!

Star clusters in that extremely remote part of our galaxy are usually very old because the gravitational influence of the galaxy is a lot less and interstellar matter's not stirred up as much. So don't expect a lot of spectacular star formation there. And if eventually a star cluster does form, it stands a much better chance of remaining compact. Berkeley 21 therefore could be many billions of years old, perhaps even be as old as our galaxy itself.

Monday, 12 February 2018

NGC2129: Others taking the credit

How many times have I already argued that appearances can be so deceiving when observing the night's sky? Sirius shines so brightly that you'd easily think it must be the biggest star out there, but then you realise it only lies 8 light-years away from us. Deneb, the brightest star in Cygnus, looks a lot fainter than Sirius from our perspective, but radiates no less than 200,000 (!) solar luminosities at us from its 1,400 light-year distance. 

Now look at this lovely open cluster, NGC2129, which you'll find on the border between Gemini and Taurus. It's an easy target even for binoculars and that's mainly due to the two bright stars at its centre. Now what if I told you that in reality these two stars aren't even remotely close to the cluster and that they only appear to be part of it from our perspective? Indeed, the brightest of the two (HD250290) is an ordinary, 3 solar mass yellow giant, which lies 1,800 light-years away. Its fainter "sister" that lies slightly below (HD250289) is a similar yellow giant but it lies at a distance of 2,700 light-years. And the rest of the cluster? Well, you'd have to travel three times as far, 7,200 light-years to be precise. So those two bright stars have nothing to do with it whatsoever, nor are they related to each other. They just happen to float in front of this lovely, remote cluster which contains about three dozen stars and which is slowly breaking up under the gravitational force of our galaxy. 


Friday, 2 February 2018

STF867: The joys of double star observing

How can you ever get bored looking at the stars? There are literally billions of them and every single one has its own personal character and story. None, however, show their particular nature as well as binary stars. It's still not clear how many stars are actually double or multiple star systems, but estimates range from 50% for smaller, Sun-like stars to even 80% for massive, hot giants. 

Many of these double stars are a real pleasure to observe, as I've already shown you many times before. Sometimes the challenge is that they're so close together that they're on the limit of what a human observer can distinguish with his amateur telescope. Procyon springs to mind. Others are easier to separate and show the most amazing, contrasting colours, like Ras Algheti. The choice's nearly infinite and I often ask the computer of my telescope to amaze me at random. And then you come across star systems that have hardly been observed by anyone, but who'll mesmerise you with their beauty.

Has anyone of you ever heard of Struve 867? It's just one entry to the enormous list of the famous 19th century German Astronomer. And yet, when my telescope turned to this little star in Orion, I was so charmed that I immediately took my sketchbook. 

The main star is a 7th magnitude white giant that shines 286 solar luminosities at us from the respectable distance of 1,300 light-years. It's companion, only 2.2 arc-seconds apart, appeared orange to me. At magnitude 8.88 it's considerably dimmer and slowly revolves around the main star from a distance of 876 times the distance between the Sun and the Earth (AU or Astronomical Unit). To give you a better idea, that's 25 times the distance from here to Pluto. They only appear almost glued to each other because they're so far away from us. 



Sunday, 28 January 2018

K 2-1: Never be discouraged

I've written this already a couple of times before, but never be discouraged by a strange object denominator. There's so much more to discover beyond the classic Messiers and NGCs and often you'll be amazed by what you find. Take this strange planetary nebula, for example. Its name is Kohoutek 2-1, after its Czech discoverer, and it lies about halfway between Elnath (B├Ęta Tauri) and Iota Aurigae. Although it's obviously not the brightest of planetaries, it immediately leapt out at me when it moved into the field of view of my binoscope. Even more so, I had no difficulties at all noticing that this particular planetary is way out of the ordinary. As you know, planetary nebulae are usually round or elliptical, hence the nick "planetary" nebulae because they look a bit like a planet. This one's a whole different league with its strange lobes and wonderful structures.

I've found very little information about this little nebula, but I suspect that its central star's binary. I did have the impression to have seen a tiny companion which I've also represented in the sketch. This would certainly explain a lot because the gravitational pull and radiation of a companion star would severely disrupt the nebula's shape.

To make the picture even more interesting, the nebula's surrounded by a lovely, loose cluster of tiny stars, denominated "Skiff 3". Again, no other information to be found anywhere. The nebula would be 3,600 light-years distant, but the for the cluster I can only guess that it lies way beyond.

Friday, 26 January 2018

NGC1555: Hind's Variable Nebula

T Tauri is a very young star that's only just emerged from the cocoon of dust and gas in which it was born. Fusion's just ignited in its core but is still unstable. Soon, this star will blow away the dust that's still surrounding it and grow into adulthood as a stable main-sequence star, fusing hydrogen into helium. 

For the moment we're not quite there yet as you can see. The star has a distinct yellow-orangy colour and varies in brightness as fusion still needs to stabilise. The surrounding dust glows in its light, obviously with the same variations as the star. I had the impression that also the nebula appeared slightly yellowish, but that's obviously an optical illusion due to the proximity of such a strongly coloured star. Still I couldn't resist adding a bit of yellow to the nebula too, for artistic reasons and because it renders the illusion at the eyepiece. 

It also seems that this nebula was significantly brighter when it was discovered in the late 19th century. The famous German astronomer Friedrich Struve reportedly found another, similar nebula very close to NGC1555 and this discovery was confirmed by others. Strangely enough, this nebula, which had been catalogued as NGC1554, couldn't be found anymore a decade after its discovery, nor has it been found ever since. Scientists now speculate that it was a transient portion of the same reflection nebula complex. 

T Tauri and its surrounding nebula lie approximately 500 light-years away.


Wednesday, 24 January 2018


Procyon, bright and yellowish, is the brightest star in the winter constellation of Canis Minor, the small dog, and the eighth brightest star in our sky. Not that it's a big and impressive star as such, but its relative brightness merely originates in its proximity. At a distance of only 11.4 light-years, Procyon is the 14th closest star to our Solar System. Let's say it lies right under our doorstep, in astronomical terms. For the rest it's nothing out of the ordinary, with a mass s.5 times that of our Sun and a diameter twice as big. It also boasts a solar-like corona which it heats up to 1.6 million °C. Procyon's much younger than our Sun though, but after 1.7 billion years it has already depleted its entire hydrogen supply and fusion has started to expand outside of its nucleus. It's preparing to evolve into a much bigger, helium-fusing red giant, which will happen in the next 10 to 100 million years.

Nothing out of the ordinary, you'd say. Yet, this inconspicuous, bright star hides a little secret. It had already been suspected in the early 19th century due to irregularities in the star's proper motion, but it was not confirmed visually until 1896. Procyon is indeed double, the main star orbited by a tiny companion that's extremely difficult to observe. Procyon B lies 4.3 arc-seconds from Procyon A, which should be doable also in small telescopes, but the problem is that A shines 15,000 times more brightly than B and therefore the little one disappears into A's glare. Even with my binoscope I had a really hard time separating the two and I had to wait for that moment of perfect seeing to detect the companion, as I've tried to reflect in my sketch.  

B revolves around A in a highly eccentric orbit which takes it as close as 9 AU (Astronomical Unit - the distance between the Earth and the Sun) and as far as 21 AU over a 40-year period. It's a white dwarf only 30% larger than the Earth but contains 60% of the Sun's mass. Its average density is therefore a whopping two tonnes per cubic inch! Scientists believe that B was once bigger and hotter than A and therefore it evolved a lot faster. When it got older, it evaporated much of its mass onto A, which gradually became the dominant star in the system. We find that A is indeed quite rich in heavier elements, byproducts of advanced nuclear fusion in B. 

No evidence for planets has been found to date and even if there were, they would probably not be suitable to sustain life due to the distortion and radiation of this extreme double star system. However, a large ring of dust has been detected. 

PS: The image doesn't show well in Blogger, but B lies slightly to the bottom-right of A...