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.