Thursday, 11 October 2018

Berkeley 4 and open cluster sketching

Loyal readers will have noticed that I've neglected this blog for a bit. The thing is that currently I'm having so many other things on my mind that astronomy sketching had to move into the background. I will keep posting new sketches every now and then, but for the coming months probably not at the pace I used to. Astronomy sketching, at least the way I do it, is an incredibly tedious passtime and apart from the one to several hours at the telescope, each and every single of my sketches involved a couple to many hours behind the pc, sometimes even days. 

Take a good look at this sketch of open cluster Berkeley 4 in Cassiopeia (unfortunately Blogger doesn't allow to magnify an image to its real dimensions so it'll be difficult to see). There must be at least 400 to 500 stars on it and none of them were randomly added. They were all observed at the eyepiece, put on paper and redrawn on the computer in an attempt to render the telescope view as realistically as possible.  

This brings me to another argument. I've been using my binoscope for over two years now and I've come to realise that I've been so terribly busy sketching that I've completely forgotten to observe. Yes, when you're sketching you're also observing in a certain sense and perhaps even more intensely so as you're trying to catch every little star or object detail that there is to see. But it's not the same thing. Last week I was standing behind the eyepieces, observing, being so carried away that I didn't feel like sketching anymore. I just wanted to relax and enjoy myself. Sketching has become too much of a race, lately. So I hope that you'll forgive me but for the coming months I'm going to enjoy my telescope a bit more and share a bit less. 

Yet, here's Berkeley 4, 10 million years old, a respectable 8.000 light-years away but yet a fabulous object in any telescope or even binoculars. It's slowly falling apart... the gravitational bonds between the many hot giant stars is ruptured by the pull of our galaxy. I think this is a fitting sketch to end a very busy chapter and initiate a more quiet one.

Cheers to all of you!

Thursday, 13 September 2018

Stephan's Quintet

In 1877, the French astronomer Edouard Stephan discovered the first galaxy cluster beyond our own local group. Being a difficult target for small telescopes, this cluster of five galaxies in Pegasus is an astronomer's treat.

Four of the five galaxies you see at the centre of my sketch actually have a physical relationship (catalogued as Hickson Compact Group 92 or Arp 319) and given their closeness and relative speeds they will soon merge with each other. The collision speed of NGC7318b (Cfr. the bottom image with labels), for instance, is so mind-bogglingly huge - we're talking about MILLIONS of km/h! - that it generates a shock wave, similar to sonic boom but travelling through intergalactic gas, that is larger than our Milky Way! The gas is heated up to millions of degrees Centigrade and starts to emit X-rays, so powerful that we can detect them here on Earth, in spite of the 210 to 340 million light-year distance.

NGC7320, on the other hand, appears to move in a completely different direction and at a much slower speed compared to us. From this we conclude that this galaxy is no part of the group at all and that it is in fact much closer to us (about 39 million light-years). 

Extremely faint and somewhat distant NGC7320c, however, seems to share the same motion of the four group members and in fact a trail of gas and dust has been detected that leads from NGC7319 in its direction. Therefore it is more than likely also a member.  

Friday, 7 September 2018

NGC40: a remarkable bow-tie

NGC40, a bright planetary nebula in the constellation of Cepheus, is peculiar in many ways. 

First of all, in a thousand years from now it will almost be near the sky's north pole. Due to a strange wobbling of the Earth's axis, the poles describe a full circle in the sky once every 26,000 years. This phenomenon, which scientists call "precession", has as a consequence that Polaris won't be the North Star for much longer. In fact, 14,000 years ago bright Vega was the closest naked-eye star to the north pole. When the ancient Egyptians built their pyramids, they made a corridor to the North Star so it would shine eternally on the pharaoh's tomb. But at the time that star was Thuban, Alpha Draconis. Polaris has become the North Star for the last thousand years or so and will be closest to the pole in a century from now, after which the pole will move into the obscure constellation of Cepheus... close to our NGC40.

Second, the "Bow-tie Nebula" has an unusually bright central star. Most central stars of planetary nebulae are "dead" white dwarves, in the sense that they've sloughed off their entire atmosphere and all that remains is an inactive, extremely hot core. The central star of NGC40, on the other hand, still seems to be very much alive and it is classified as a Wolf-Rayet star. Those are stars which were originally so massive that, even after they've shed a large part of their atmosphere, they can still regain some sort of stability and continue fusion in the now exposed core. For this reason NGC40 bares more resemblance to Thor's Helmet and the Crescent Nebula, which originated from similar Wolf-Rayet stars. Over time, the white dwarf of an ordinary planetary will cool down and fade. In the case of NGC40, there's no cooling down whatsoever and the star's still radiating at a scorching 90.000°C! Wolf-Rayet stars usually end their lives violently in a supernova explosion, so NGC40 probably hasn't reached its grand finale yet.

Another odd thing is the nebula itself and, more precisely, its outer rim. With my binoscope (but also with more modest instruments) this bright rim's easily visible. What I also noticed was that it exhibits a flattened shape, rather than being perfectly round or elliptic as one would expect. The flattening is caused because the ejected gas bubble has grown almost a light-year across and has reached interstellar space, where dynamics are different. The rim's having ever greater trouble ploughing through this new medium and its expansion speed has slowed down to "only" 10 km/s. 

Of course you can't see this at the eyepiece of an amateur telescope, but this planetary shows up red in photographs, instead of the usual blue-green. This definitely raises a few eyebrows because with such a hot and active central star you'd expect that the nebula gets excited to much higher temperatures and hence appear bluish. There are a couple of explanations for this. The nebulosity may contain a high level of dust which emits a lot in the infrared. Or more intriguingly, the central star is currently still blowing off mass at an incredible (but typical for WR stars) 1,800 km/s! Much of the star's radiation may therefore be absorbed by the new and rapidly expanding shell of matter.  

Clearly there's still so much to be discovered about this nebula as to become an astronomer's lifetime study.

Sunday, 2 September 2018

NGC6803: More complex than one might think

Not even a degree from NGC6804 resides another planetary nebula. NGC6803 appears much smaller than its neighbour, but this is only because it lies much further away from us (10,000 light-years). This means that amateur telescopes will not reveal much more than an almost stellar-like object. Even with my binoscope at 507x, details were difficult to make out, although I did see its very hot central star (surface temperature 90,000°C!) surrounded by a bright, elliptical shell with two opposite lobes.

This bright shell is of particular interest because it contains much more elements such as carbon, oxygen and neon than most other planetary nebulae. These unusual abundances suggest that its central star was born in a metal-rich zone in the later stage of galactic evolution. Possibly the nebula's progenitor star could have been a star similar to our Sun but part of a close binary system. The matter exchange between both components, rich in heavier elements as byproducts of nuclear fusion, contributed to the abundances we now observe in the nebula. Comparison with data from 1995 shows that the shell has become much denser over this (astronomically) very brief period and indicates the existence of very complex structures. Obviously much more research needs to be done.

Thursday, 30 August 2018

NGC6804 and its curious dust disk

NGC6804 is a fairly advanced planetary nebula in the constellation of Aquila, the eagle. In spite of its distance of 4,200 light-years, a high surface brightness makes this nebula an easy target for small to medium telescopes. Its outer shell has reached a diameter of 1.3 light-years and therefore its expansion is slowing down due to the interaction with interstellar space. 

Yet there's more to this fine planetary than its three shells reveal at first sight. Invisible to human eyes, this planetary emits a significant amount of radiation in infrared wavelengths, much like NGC7008. The cause for this is a large dust disk surrounding the white dwarf, probably rubble and debris of a planetary system that once existed but that has died along with its progenitor star. Within the next 5 billion years, also the Earth will follow the same tragic fate.

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


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.  

Friday, 20 July 2018

Kappa Herculis: Not what it seems

Did I already mention that appearances can be very deceiving when looking at the night's sky? Wait until I tell you about Kappa Herculis!

Kappa Herculis, also known as Marsic, is a fine double star that can easily be separated with small telescopes or even binoculars (separation 27"). Though their measured temperatures are almost identical (4990°K for K Her A and 4650°K for K Her B), most observers - including me - see them as bright yellow and orange. Their luminosities are 170 and 70 Suns respectively and they have radii of 3 and 2,5 times solar. This means that their respective ages are 400 and 700 million years. Nothing out of the ordinary so far... er...

What did I just say? Two components of a double star that don't share the same age? Highly suspicious! Now, if we measure their distances we find that A lies 388 light-years away from us, whereas B is almost 100 light-years further away! Okay, given the proximity of A, the measured distance to B has a large uncertainty so they still could be near to each other. On the other hand, in the 300 years that this double star has been observed, their separation has diminished from 57" to 27", much more than it should. 

Conclusion: This is no double star but merely an incredible line-of-sight coincidence!

Yet it does seem that A is a binary star with a small companion an arcminute away, which would be 7,500 times the distance from Earth to the Sun, and with an orbital period of 340,000 years. From A, this tiny companion would shine with the same brightness as Saturn.

To make things even more confusing, there's also 8 Her, the bright, white star above our "double" on my sketch. It appears that 8 Her is 367 light-years away, more or less the same measured distance as K Her A! Could they be a real pair? Unlikely, since in that case they would be 1.3 light-years apart, too far to maintain a gravitational bond. Their apparent motion across the sky also appears different. 

Even if 8 Her and K Her A are not related, the former doesn't seem to be ordinary as well because it's an extremely fast rotator. It spins at an amazing speed of 259 km/s, only slightly under the limit at which the star would tear itself apart, resulting in a rotational period of 10.3 hours. 

Friday, 13 July 2018

M21: Young and bright

Another pretty and well-known star cluster in Sagittarius is M21, only half a degree away from the famous Trifid Nebula. Containing only 57 confirmed members, it's not as well populated as M23, but nevertheless it's a beautiful object in binoculars and small telescopes. As was the case with M23, the binoscope magnifies just a bit too much to frame this cluster nicely and you're almost getting the impression that you're looking though it. Still, it lies 4,200 light-years away from us, double the distance to M23 and in fact not all that far from the Trifid. Therefore most of its stars appear somewhat dim, although a bright blue supergiant, ten times our Sun's diameter and radiating 64,000 times as much energy, stands out centrally. Many cluster members also appear to be close binaries so in reality the total star count should be a bit higher. 

Interesting to note is that this cluster's still extremely young, hardly 4.6 million years old and therefore not much older than the human species.  

Tuesday, 10 July 2018

M23: comparison Nexus 100 binoculars vs. 18" binoscope

A week ago I showed you M23 as seen through an 18" binoscope, commenting that such a large instrument is probably too big for such an extensive object. So A few days later I re-observed this amazingly beautiful star cluster with my Nexus 100 binoculars at 24x. 

I have to tell you that I was somewhat disappointed because appearing so exaggeratively bright in the binoscope, I had expected something more spectacular in the 100mm binoculars. The cluster was, of course, clearly visible at first glance, but it took a while for all the tiny individual stars to reveal themselves and the overall appearance was slightly faint.

What can I say? I admit that I haven't used the binoculars for over two years, at least not since I got the gigantic binoscope, and therefore my mind's probably got used to quite another level of brightness and detail. It's very easy to get used to larger aperture, but downscaling's a different matter. 

Does this mean that I'll but the Nexus up for sale? NOT IN A MILLION YEARS! It's simply a different kind of observing, a kind that I've neglected for far too long and that I need to take up again some more. Big binoculars are not meant to bring out tiny details or to show you a star cluster scattered across the entire field of view. Contrary to telescopes, they're meant to take you on a sightseeing trip around the heavens, giving you a taste of every splendour that's up there. From M23 I quickly jumped to M20-M21 (nicely in the same field of view of course), then onto M8, M22, M24 (completely in the field of view), M25 and M16-M17 (almost in the same field of view). All of this without hardly having to move from my comfortable chair. That's the difference.

Anyway, here's my M23 sketch. To the bottom you'll find the sketch I made with the binoscope for comparison.



Thursday, 5 July 2018

IC4634: not going quietly

I got the question why the heck I'm so passionate about these tiny planetary nebulae. Indeed, most people only see a blurry little dot and what could possibly be interesting about that? Well, most people simply don't look very well. Even though usually bright and easily visible, it takes some time for your eyes to adjust to the image and to discover all possible details. Next time you're looking though a telescope, try staring at this little dot for at least two full minutes, let your eyes move around it, relax, take it all in. Suddenly there will be a point at which you can see more... structures... filaments... 

IC4634 is still a young planetary nebula, hardly a few thousand years old, and unfortunately it lies a respectable 7,500 light-years away. So yes, it looks tiny. This is a real pity because this is a truly spectacular little bugger. The dying central star (which I had difficulty making out) is not ejecting its atmosphere in one big blow, but in puffs whilst it keeps spinning rapidly. The result is that the gaseous shells form expanding waves in different directions. Difficult to see, I know, but it was definitely there. I also had the impression that I could see a faint halo around it, which may be material the star already ejected when it was in the last, unstable phase of its life and which now slowly begins to glow under the tremendous radiation from the remaining stellar core.

Wednesday, 4 July 2018

NGC6507: My cup of tea

A few days ago I showed you brilliant M23, an open star cluster in Sagittarius that's a real treat for binoculars and small telescopes. In a large telescope you'll have a hard time trying to fit everything in the telescope's eyepiece and therefore the view will become somewhat less pleasing. Now onto a small cluster in M23's vicinity: NGC6507. There's surprisingly little information to be found about it and that's a real shame because this is the sort of object I (personally) go nuts about. Being over 3,900 light-years away it lies almost twice as far from us as M23 and if it doesn't nearly appear as impressive it's mostly due to its much greater distance. Observe it with a sufficiently large telescope and you'll be surprised about the number of tiny little stars that appear in between the brighter ones. Well... brighter ones... even those are of mag. 11-12. 

Now try to focus on what this cluster's telling you. Look at how its stars are no longer contained in a more or less spherical shape but how they seem to be smeared out somewhat. Clearly, this cluster's already a bit older than M23 (400-450 million years) and the effect of our galaxy's gravity is taking its toll. Its stars are being pulled into a streak along our galaxy's plane and will then disperse to lead their adult lives in solitude. 

Again, the brightest star, towards the bottom-right, lies much closer to us and therefore doesn't belong to the cluster at all. 

Monday, 2 July 2018

Glorious M23

This may sound a little weird, but sometimes a telescope can be too big. Last night, for example, I observed M23, a bright and rich star cluster which lies 2,100 light-years away in the direction of the centre of our galaxy. The largest true field of view my binoscope can offer is less than a degree across, which is a tight fit for this big and relatively close cluster. The view in binoculars or small telescopes, albeit less bright, will certainly be more pleasing but hey... it wasn't all that bad in my binos after all. 

M23 contains about 150 confirmed members and came into existence some 300 million years ago, making it a not a very young cluster. In spite of its many members, it's now starting to break up slowly, after which all of the individual stars will go their own way. For many of them this journey will not be long because bright blue giant stars lead very short lives. The bigger a star, the faster it will burn its fuel and there are quite a few biggies in M23, some of which are already shutting down hydrogen fusion and are evolving towards red giant status. Through my binoscope on the other hand, most of the stars still appeared bright blue as I've tried to reflect in my sketch.

Once more I have to inform you that sometimes appearances can be deceiving because the very bright star near the bottom-right border (HR6679) doesn't belong to the cluster at all. Being only 320 light-years away it's a lot closer to us and with its 2.2 solar masses I wouldn't exactly call it a giant.

Wednesday, 27 June 2018

NGC5694: bye bye Milky Way

After last week's spectacle with M80, pointing your telescope at globular cluster NGC5694 can be a bit disappointing. It lies deep in the tail of Hydra, the water snake, and with small to medium-sized telescopes you'll either have to be very lucky or have the eyes of an eagle if you want to resolve any stars in it. Still, NGC5694 is not only bigger but also a lot more interesting than its brighter counterpart in Scorpius. 

The reason for its relative faintness is its distance - a whopping 113,000 light-years, making it one of the most remote known globulars of our Milky Way. Furthermore, its position at the far end of our galaxy implicates that a lot of its light's being absorbed by interstellar dust, making it appear even fainter than it already is. Its extremely low metals content (meaning any substance heavier than hydrogen) makes us conclude that it must be one of the oldest known globular clusters and hence one of the oldest known entities in our Universe. You may recall that globular clusters are usually older than the galaxy they accompany. In the case of NGC5694, its age has been estimated to be no less than 13.4 billion years! If you compare this to the estimated age of our Universe, 13.8 billion years, you'll realise that this cluster and the stars of which it is composed already came into existence shortly after the Big Bang. With "shortly" I mean in astronomical terms of course. 

Now we move on to interesting fact number two. NGC5694's approaching us at the unusually high speed of 144km/s, but relative to our Milky Way's centre it's zooming past at 273km/s. Warp factor 9, Mister Scott! At the cluster's distance from the galactic centre, this is 60% higher than the escape velocity, meaning that NGC5694's definitely leaving our galaxy and will never come back. 

A 1976 study suggests that a high-mass object may have flung NGC5694 into its fast, hyperbolic orbit and that the Magellanic Clouds may have been the culprits. The same study also theorises that this globular may even have belonged to one of these dwarf galaxies after which the tidal forces of our galaxy tore it away.

So, doesn't all of this make this faint little blob a little bit more interesting than you would have guessed at first sight?

Monday, 25 June 2018

Saturn revisited

I rarely sketch the Moon or planets. They're terribly demanding objects if you want to capture them properly and all in all I've never been a passionate planetary observer. Perhaps I'm still influenced by my childhood, when I passed many happy Saturday mornings (and nights) at the Urania observatory near Antwerp, Belgium. After a one-year introductory course we got to choose between the various working groups in order to participate in miscellaneous projects under the supervision of the group leaders. These groups were i.a. Solar System, Comets and Meteors, Weather, Photography and during my final year there was even a Maths Group! Can you believe it? 14-15 year old kids that go to the observatory on a free Saturday to study Math! Hardly surprising they only had two members.

Without a minute's hesitation I chose Deep Sky, the group that focused on everything beyond our solar system. It was by far the most popular group and it also had the funniest and most popular leaders. There used to be some sort of playful rivalry between the groups and especially Deep Sky became increasingly notorious for havoc and disaster. We disturbed a funeral whilst measuring the speed of sound (because the guys making the sound pulses simply didn't realise what was going on at the church at the other side of the car park), we broke down a three-dimensional model of dozens of stars of Ursa Major which had taken others months to assemble (it was an accident, I swear) and someone had mistaken the weather group's rain gauge for a urinal (it looked exactly the same anyway). Later, when leadership of the Deep Sky group passed on to me, this didn't improve at all and on many occasions we touched the very limit of what the others considered bearable. That being said, in spite of being noisy and a bit out of control, no-one can deny that eventually we were the most productive and passionate group of them all. In the era before Internet and mobile phones we had organised a telephone chain and minutes after I had given the alert we were all on our way to the observatory to do an all-nighter of serious deep-sky with the good old (and very awkward) 25cm Kutter telescope. We laughed and we cheered and we booed at the other groups, we went to the chip shop at 1 and to the baker's at 4 (for oven-fresh buns - you had to see the baker's face when we entered his workshop at this rather unusual hour) and we watched the sun go up from the telescope tower's balcony (and we watched the neighbours opening the curtains of their bedrooms in peejays... and closing them again right away). But in the end we all went home with a map full of new drawings and dreams of the many sparkling or faint objects we had observed. We became a bunch of eternal friends and we took the oath of Deep Sky forever. 

Unfortunately, it was not to be. Tension between the various groups escalated into a serious conflict and after 5 years of dedicated leadership I was given the sack. It's something that I still feel bad about, although I must admit that my autistic nature didn't provide me with the maturity to run the group properly. On the other hand I daresay that Deep Sky had become so popular, especially under my leadership, that I had to manage twenty kids whereas the other groups hardly had any members left. Perhaps because children need some time off during the weekends and prefer doing astronomy in a playful way, not in detention? Yet, even if all of this hadn't happened, I realise now that nothing can last forever and eventually even I, the perpetual, curious, autistic kid, had to grow up. 

The disdain for the Moon and planets's still a bit there though. :-)

And with labels...


Friday, 22 June 2018

M80 - Out of the shadow

M80 is a globular that's sadly neglected because of the vicinity of predominant M4, which seems so much bigger and brighter. Yet, it's about time that we change all that because M80's a true marvel to behold. 

Actually, M4 only seems much more impressive because hovering at only 7,200 light-years away it's one of the closest globular clusters to our Solar System. In reality, M80's nearly fifty percent bigger and brighter and it still is an impressive sight, even from its more than 32,000 light-years' distance. Containing several hundreds of thousands of stars in a sphere not even one hundred light-years across, it's one of the most densely populated clusters. Yet I had absolutely no problem resolving it completely and I noticed a myriad of lovely star chains and structures. It also appeared even more bluish than most of its kin. I can only speculate that, due to its density, star atmospheres get blown away even more easily through interaction with other stars, exposing the hot, white-blue interior of the otherwise very old stars. As you may recall, globular clusters are among the oldest entities in the universe, often older than the galaxy they accompany. Another explanation is that this particular cluster contains an exceptionally high number of so-called "blue stragglers", very young stars that have been captured by the cluster. 

So next time you point your telescopes at Scorpio, please don't forget this little jewel.

Monday, 18 June 2018

NGC6567: a planetary in full expansion

Young planetary nebulae are not always easy to find because of their tiny size they usually resemble an ordinary star at low telescope power. Yet, with the aid of a nebula filter - UHC or OIII, which blocks all light frequencies apart from those predominantly radiated by these nebulae - they easily stand out as a bright and somewhat fat star against the dark background. If you then increase magnification to as much as your telescope or sky conditions allow, you'll often be surprised. Due to their high surface brightness they let you use extreme high power and not seldom show some extraordinary detail.

Take this little bugger, for example. NGC6567 lies some 4,000 light-years away from us in the direction of the marvelous Sagittarius Stellar Cloud. It gets lost somewhat in the extremely rich star field of the centre of our galaxy, but with the aforementioned method you'll still be able to find it without too many difficulties. At 507x it becomes obvious that this is a planetary nebula and not a star. What's more, its bright inner ring, an enormous bubble of ionised gas that the dying star's expelled some 4,000 years ago, just leapt out at me. This bright bubble's currently expanding at 13km/s, which is not exceptionally high. Yet without any doubt this nebula will become much more spectacular in the course of the following millennia, when it will expand further.

Sunday, 10 June 2018

The Eskimo... again...

In one of my first posts I talked about NGC2392, otherwise known as the Eskimo Nebula for obvious reasons. It does look like a head wrapped in a parka hood, doesn't it? 

This winter, during a very clear (but teeth-chattering cold) night I finally pointed the binoscope at it and pushed power to 507x. There are these moments when an 18" binoscope not just performs on par with high-quality photographs but even outperforms them. This was one of these moments. 

Astronomical sketching is a very subjective form of art and often artistic creativity tends to take the upper hand on true scientific observation. It's a delicate balance because we sketchers want to show the viewer every detail we (think we) have spotted. Observation through a telescope, however, usually resides at the very edge of what a human eye can possibly capture; staring at a faint object for minutes if not hours, direct vision, averted vision, trying to avoid any external interference. Sometimes it gets so bad that the whole image starts dancing in front of our eyes, especially with one-eyed viewing, and we get overwhelmed by fatigue. Therefore it's generally so hard to tell whether certain details were really observed or merely intuitively suggested. 

Then there's the question of how you want to represent these faintest of details. If you draw them clearly, the image easily gets "overdone" and albeit artistically pleasing and massively impressive, you can't really state that that's exactly how you've seen the object at the eyepiece. Any viewer who'd look through a telescope after being wowed by such a drawing would be seriously disappointed. 

Personally, I prefer to draw everything as realistically as possible, even if I have to make some details all but invisible. This may perhaps result in less impressive sketches and I've already read a lot of criticism on my work on-line, like someone claiming that he can see a lot more with his 9,25" SCT. Well, if that's the case, I'm very happy for him. My aim is to give the viewer (hopefully) the same challenge as I had behind the eyepieces. "Can you see it or not?" I don't care if my sketches don't look as fancy as some others. 

Astronomical sketching is not a competition.  

Yet, in the particular case of the Eskimo, I didn't have to hide any details at all because this is exactly how it appeared at first glance.

Friday, 25 May 2018

NGC3242: Jupiter's Ghost

Low on the horizon, for northern observers, during the early spring months... in an otherwise seemingly empty part of the sky you may stumble upon this big and bright planetary nebula. It's popular name "Jupiter's Ghost" refers to its similar apparent size and shape compared to the biggest planet of our solar system. In reality this nebula is some two light-years across and is still in full expansion. It merely appears the size of Jupiter because it is 1,400 light-years away.

The bright inner halo, the central star's dying breath, was blown into space some 1,500 years ago and is now rapidly catching up with the large outer shell which gradually built up during the final phase of the star's life. It's central star of 11th magnitude was not that easy to see, although it's radiating at over 150,000°C and lighting up the gas bubble around it. The gas is heated up to the extent that it begins to ionise and emit a bluish-green light of its own. Actually, we're catching this nebula right at its brightest phase. Within the next couple of thousand years it will expand further, fade and eventually dissolve into space.

Thursday, 17 May 2018

NGC5005: Black holes lead to star formation?

Yes, I know, it's a bit of a strange title for this post. Let's have a close look at NGC5005, a galaxy that's not in our immediate vicinity (estimates vary greatly from 45 to 113 million light-years, with an average of 65). It's a fairly bright galaxy in Canes Venatici, the hunting dogs, which can be seen quite easily with a modest telescope. 

Through the binos at 285x, it revealed a wonderful amount of detail, such as the darker arc on the left. But what we're really interested in, is its nucleus. Spectroscopic analysis revealed that the heart of this galaxy contains a lot of non or weakly ionised atoms, such as O, O+, N+, and S+. Scientists classify galaxies with such a cloud of weak ions in their core LINERs, which stands for "Low-Ionisation Nuclear Emission". This is nothing unusual and as it appears up to a third of all galaxies could fall under this category. The question however, is what causes this enormous cloud, which may swirl inward up to 750km/s! Scientists are still heavily debating on that, but significant x-ray emissions in the case of NGC5005 seem to confirm a super-massive black hole in its centre. Another observation that we make, is that this ion cloud produces some serious star formation. Usually not a lot of stars are formed in the nucleus of a galaxy, which therefore contains an older star population, and most starburst activity is generally concentrated in billowing spiral arms. 

So may we conclude that a black hole can be so powerful as to cloak itself with a cloud of ionised gas in which thousands of new stars are born? 

Thursday, 3 May 2018

Frosty Leo... again

I've already written about this highly unusual planetary nebula in construction two years ago and will repeat most of this post here, to give you some background information on IRAS 09371 + 1212, or in other words "Frosty Leo". 

When I made my first observation, I was unfortunately limited to 200x, which is far from sufficient if you want to see some detail in this tiny puff of mostly water crystals. So here's my recent observation with the binoscope and... yes... at 507x details were abundant!

Nature is ruthless. It gives life and make stars sparkle so brightly in our sky that uncountable poets have dedicated their most beautiful work to them. But unfortunately, all beauty must fade and everything that has a beginning also has an end. Even so the seemingly perpetual stars which eventually have to die too. I've repeatedly written about dying stars, either the ones that go fairly quietly through the formation of a planetary nebula, or the ones that grant us the unforgettable spectacle of a supernova explosion. Today, I'd like to show you a star that's literally exhaling its dying breath. We're talking about a so-called protoplanetary nebula, nicknamed "Frosty Leo", and this nickname isn't far-fetched at all as I shall explain. 

When a small to medium-sized star reaches the end of its life cycle, it runs out of fuel to sustain nuclear fusion and becomes highly unstable. Its interior collapses and the shock wave that this causes literally blows the star's atmosphere into space, where it will form large gaseous shells or "bubbles" around the remains of the star. The contraction of the dying star's core will in turn generate so much heat that it will reignite fusion of helium into heavier elements, such as carbon, oxygen and even iron. The star's radiation continues to blow up the "bubble", which eventually dissipates into space, and heat it up to a point where the gas ions start to emit light as well. This is what we call a "planetary nebula". 

In the case of Frosty Leo, however, we're not quite there yet. We're actually witnessing the collapse of the star and the initial expulsion of its atmosphere. Its last breath, as a matter of speaking. At this low magnification it's almost impossible to see, but the star's atmosphere is blown away in two opposite lobes which keep expanding at a rate of a whopping 25km/s. Remember that in order to escape from Earth's gravity a rocket needs an initial velocity of 11,2km/s or 33 times the speed of sound, so imagine how fast the nebula around Frosty Leo is forming!

As I said, the nickname wasn't chosen by chance or after a very successful party because its discoverers had to celebrate their findings. No, the nickname derives from the fact that the nebula consists for a large part of... water-ice grains! Plus of course that it resides in Leo. For the time being it's perhaps the only such nebula that we know of, so this makes it doubly interesting. Another weird fact is that it lies 10,000 light-years away from us and an unusual 3,000 light-years above the galactic plane. Therefore it must have been a very lonely star, condemned to die in complete isolation.

In the next millennia Frosty Leo will keep expanding and eventually the nebula, which currently only reflects the light from the star, will light up, adding another Crystal Ball or Eskimo to our skies. But let's not be impatient. This object is already a great spectacle and much more so from a scientific standpoint. 

Monday, 30 April 2018

M94: a galaxy that's difficult to explain

In the area of the M51 group of galaxies, but considerably closer to us, at 16 million light-years, lies this little treasure. M94 is definitely one of the most spectacular galaxies in the Messier catalogue, as we see it face-on and also given it's fairly high surface brightness. In larger telescopes it becomes obvious that this isn't just a normal spiral galaxy but that it consists of a bright inner ring (with complex spiral structure), some 50,000 light-years across, and a faint outer halo that extends at least 30,000 light-years beyond that. 

For the time being, scientists are having difficulties finding a plausible explanation for this odd, double-ring shape because both the accretion of a smaller galaxy or interaction with a neighbour don't seem to add up in this case.  What's more, there appears to be very little dark matter present in it. This is very controversial because current models fail to explain how a galaxy could form without a sufficient amount of dark matter.

There's more. At first it was believed that the bright, swirling inner structure was by far the most active region in this galaxy and we do observe some serious star-forming there indeed. Recent IR and UV studies, however, revealed that the outer halo is not an ordinary ring of stars, but a complex structure of spiral arms which is surprisingly active. In fact, there's twice as much star formation going on in this outlying region and also this raises some eyebrows. A possible explanation could be that star formation in the outer halo is simply more efficient.


Sunday, 22 April 2018

M63: a spring sunflower

Sunflowers are usually a thing of summer, but there's a very peculiar one that blooms in spring already. Point your telescope, or even your binoculars, under the big dipper's handle and you'll easily find this spectacular galaxy. Number 63 on Messier's list looks very much like a sunflower indeed, with it's bright, yellow core and flocculent spiral arms. Unlike "grand design" spiral galaxies, the spiral arms of M63 appear patchy, like a heap of cotton balls. It was also one of the first galaxies in which a spiral structure was recognised, by Lord Rosse, halfway the 19th century. 

The Sunflower Galaxy lies approximately 37 million light-years away from us and is a part of the M51 galaxy cluster, along with a few smaller ones. 

Physically, the Sunflower is a very active galaxy and every knot is an area of intense star formation. More interestingly, photographs revealed a wide halo around it which materialised most likely after an encounter with a dwarf galaxy, somewhere within the last 5 billion years. From the specific properties of the stars in this halo, scientists believe that this dwarf galaxy might have originated in our own local galaxy group.

Now as for the cherry on the cake: look slightly to the left of our Sunflower and you may spot a tiny smudge. No, it's not an extended part of M63, nor is it an accompanying dwarf galaxy. It's proper motion, a breathtaking 23,500km/sec away from us or almost 8% of light speed, is far too great for it to be anywhere near M63, or within the boundaries of our area of the known Universe. It's a giant galaxy, denominated PGC4018103, three times the diameter of our Milky Way, that lies 1.2 BILLION light-years away from us. As such, it's probably the most distant object I've observed so far. Just imagine... The few photons of this galaxy that I managed to capture with my eyes, left their origin when the first multicellular life-forms emerged in the Precambrian seas.

Tuesday, 17 April 2018

EGB6: Interesting faintness

Yes, I simply love the challenge of spotting extremely faint objects and especially large, frail planetary nebula in the last stage of their existence. As you know, when a star dies, it suddenly expels its outer layers which are subsequently blown away by the violent radiation of the remaining stellar core, the so-called "white dwarf". After many millennia, however, these shells of hot gas grow so large and thin that they start to dissolve in the void of space. This is exactly what we witness here, in this extremely large planetary that was discovered in 1984 by Ellis, Grayson and Bond. Visually this is one of the toughest objects to see and it was not without difficulty that I managed to discern its broken annular shape, with its western rim slightly brighter. Nevertheless it was just a tad easier than PuWe1, which was really on the limit of visibility.

How difficult they may be for us, humble visual amateurs, these extremely old and diffuse planetaries offer a great opportunity for scientific study, more specifically in the way they dissolve into space and how their central star extinguishes. In the case of EGB6, another very interesting discovery was made. Strange infrared emission knots in the spectrum of its central star, pointed to the existence of an obscure companion star, probably a faint red dwarf. Recent observations with the Hubble space telescope, revealed that some of the expelled matter of the central star was captured into an accretion disk around this companion!

Sunday, 8 April 2018

M3: autism power!

I hate sketching globulars. Really, I hate it. The reason for that is obvious... there are simply too many stars to sketch and after hours staring at them through the eyepieces you're overwhelmed with dizziness and a hammering fatigue. You're craving to go to bed and cursing yourself because you stubbornly set out on a job that you knew was going to be impossible from the start. But there you are... half a page filled with stars and still another half to go. Should you give up and let all of those hours of work be in vain? Or should you continue unabatedly, even though you can't think straight anymore and every muscle in your body's throbbing and aching?

In the end it took me almost two nights to sketch all of this, and then almost an entire month behind the pc in order to turn it into a somewhat realistic digital image. So please, don't expect me to do this kind of insane sketch often. 

But perhaps this sketch was appropriate in this time of the year, when we're celebrating autism week, because in a sense this sketch shows what an autistic person is capable of... which extraordinary talents and rock-hard determination may lay hidden under that often absent gaze. 


About M3, it's one of the brightest globular clusters in the sky, just under the limit of naked-eye visibility. At a distance of 33,900 light-years, it lies beyond the centre of our Milky Way. Only 180 light-years across, it contains some 500,000 stars! Globular clusters are among the oldest entities in our universe, often being older than the galaxy they accompany. Therefore the stars in those clusters are also among the oldest and reddest (coolest). Strangely enough, these globulars appear mostly bright and blue through a telescope. The reason for that is that these stars are packed together so much in such a small volume that their outer layers are often stripped away through tidal interactions, exposing their hot (blue-white) interior. The blue colour I added to many of the stars in my sketch was not observed as such but was added as a random effect to create more depth (a globular truly looks three-dimensional through a binoscope) and to reflect the cluster's brilliance and overall bluish appearance.

Thursday, 15 March 2018

NGC4244: A silver needle

Galaxy season's upon us again... that time of the year where the Earth turns away from the galactic plane in the northern hemisphere and more easily shows us the marvels that lay way beyond our Milky Way. Not that far away from us, at merely 14 million light-years' distance, lies a group of galaxies in the small but wonderful constellation of Canes Venatici, the dogs that hunt the great bear. Last year I already talked about the highly irregular "Train Wreck Galaxy", this year I'm taking you to its spectacular neighbour, NGC4244 or better known as the "Silver Needle Galaxy". 

There's no need to explain this nickname because the minute you point your telescope to it, you'll understand where it came from. It's one of those galaxies we see edge-on and for this reason we see it as a long streak with a brighter and wider area at its core. Yet, from the peculiar clumping of stars along its disk scientists conclude that it must have very loose spiral arms.

Sunday, 11 March 2018

IC2177 + RCW2/Gum1: The Seagull

On the border between the constellations of Canis Major and Monoceros flies a giant seagull, which astronomers identify as IC2177. Of course we're not talking about a bird but about an enormous hydrogen cloud in which active star formation takes place. This cloud spreads over such a great distance (3° across, the diameter of 6 full Moons!) and its surface brightness is so low that it can be quite challenging to observe visually. Even with my binoscope under a fairly decent sky, the body and wings of the Seagull Nebula merely appeared slightly brighter than the background. The seagull's "head" on the other hand, was more easy to make out around the bright star HD53367 (the "eye"), including some structures and a dark lane that ran from the nebula's centre towards its eastern rim and in which many people see the seagull's beak. 

The star HD53367 is quite interesting in its own right as it shows an unusual pattern in its spectrum. Scientists classify stars with this sort of pattern as "Be stars", more famous examples of which are Gamma Cassiopeiae and especially Achernar on the southern hemisphere. The reason why these stars emit these strange lines in their spectrum is because they spin so rapidly that they not only become very oblate, but that they also expel so much gaseous matter under the centrifugal force that it forms a disk around the star itself. This disk scatters the light from the star in such a way that its spectrum's altered. 

Lying almost 4,000 light-years away from us, the Seagull Nebula is producing literally hundreds of new stars, many of which illuminated the field of view of my telescope like a Christmas tree.



Thursday, 1 March 2018

NGC2022: Unnamed and underestimated

It amazes me time and time again that some of the most exotic and least-known objects still carry a popular nickname. Take IC418, for example, the Spirograph Nebula. Not that our Spirograph doesn't deserve a nick, much on the contrary since it's such a beautiful object. But then what about NGC2022, the brightest planetary nebula in Orion? It's a very popular nebula but still no-one seems to have found a nice name for it. 

I guess that the reason for this is that it's so small, although far from as small as IC418. In small to medium-sized telescopes NGC2022 appears almost stellar and you need a bit of aperture and especially very high magnifications in order to bring out some detail. At 507x, however, the bright ring of its inner shell stood out brightly against the thin haze of its outer envelope. Inside of the ring I saw strings of matter connecting it to the 16th magnitude central star, surrounded by abundant detail. I even thought to have caught a glimpse of a tiny star that looks as if it lies on the western part of the ring.

Distance estimates are always difficult with nebular objects and our best guess is that this nebula lies about 8,000 light-years away, so more than double the distance to the Spirograph. Yet, NGC2022 dwarfs it in size, indicating that it is far more evolved with its bright inner shell having almost caught up with its outer, which stretches over a light-year across. The extremely hot (surface temperature 108,000°C!) white dwarf whence the nebula originated has probably reached the point of maximum heating, after which it will cool down and extinguish slowly. 

To me, the nebula looked very much like a grape so I'd like to baptise it officially "Grape Nebula". Perhaps you have a better proposal for a nickname? I'm all ears... :-)

Friday, 23 February 2018

NGC1964: More black holes

Galaxies are entities far beyond the power of our little human brains to grasp. Yes, we think that we understand what they are because we see their nucleus and the spiral arms that whirl around it. But do we really realise what it is we're seeing? Do we, for instance, really understand that the billions of stars that make up the Milky Way that spans across the sky only comprises but a small part of our own galaxy? Do we really have any idea what hundreds of billions of stars actually mean? How much is a hundred billion anyway? And given that there are at least a hundred billion galaxies in the visible universe, each containing hundreds of billions of stars, it would be sheer arrogance to state that the Earth lies at the centre of the Universe and that we, tiny humans, are its divine culmination. 

Now point your telescope again to Orion's feet, to the unknown constellation of Lepus, the hare. In my previous post I've shown you an unexpectedly beautiful planetary nebula in that constellation. Now I'd like to show you a distant galaxy there. NGC1964 lies about 65 million light-years away from us. That's not exceptionally distant since our universe has a radius of over 13 billion light-years, but still, the light of this galaxy started its voyage to Earth around the time that the asteroid, which caused the extinction of the dinosaurs, hit us. So that's a considerable distance. The thing that struck me at first glance, was that this galaxy has a very bright, almost stellar-like core. It immediately reminded me of M77, a galaxy which has a particularly big black hole in its nucleus. The strange thing about black holes is that they're not really black as seen from Earth, but as a matter of fact they're very bright. That's because matter clumps together around it, pulled in by its enormous gravitational force, and becomes extremely dense and hot. So when you see a galaxy with a core like this, rest assured that it contains a super-massive black hole!

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.