Monday, 20 November 2017

IC405 and the runaway star

AE Auriga is a very peculiar giant star. It's radius 7 times solar is quite impressive and its 23 solar masses make it definitely a member of the most massive stars club. But this is not the main reason why this star's so out of the ordinary. What does make it so special is that it travels through our corner of the galaxy (well, 1,700 light-years away) at the breakneck speed of 200km/s! Now, if we take the star's estimated age of 2,2 million years and trace its movement all the way back, we find that it originated somewhere in the vicinity of the Orion Nebula! Until recently it was believed that AE Auriga, with Mu Columbae and 53 Arietis, were hurled out of the Orion Nebula together by some sort of cataclysm, like a supernova explosion or a near collision. However, recent measurements by the Hipparchos satellite reveal this to be highly unlikely and the three runaway stars have most probably different origins, albeit still within the Orion complex of star forming regions. 

Currently, our giant star's travelling through a cloud of gas and dust in the constellation of Auriga, the charioteer, which is reflecting its bluish light. The star's high velocity's causing a bow shock and leaves a trail of hot gas in its wake: IC405, better known as the "Flaming Star Nebula". It does seem as if the star's on fire and emitting fumes, isn't it? 

Friday, 17 November 2017

Uranus

Uranus is the seventh and before-last known planet of our Solar System and was the first to be discovered in recent history. Although it is just visible to the naked eye under dark skies, it has always been mistaken for a star until William Herschel realised it was a planet, back in 1781. 

Uranus is the third-largest planet of our Solar System, being only slightly larger than Neptune, but contrary to its more distant cousin it has no internal heat source. This makes it an extremely cold planet, with temperatures varying around -220°C in its outer layers (being a gas giant it doesn't have a solid surface). Its featureless, blue-greenish colour is caused by the large presence of methane in its atmosphere.

As dull as Uranus may look through earthbound telescopes, it is definitely very interesting in a lot of ways. First of all, it is the only planet that's severely tilted with respect to its orbit. Scientists believe that it may have been knocked over in a collision with another planet, early in its history. Also the orbits of the 27 known moons exhibit the same 97° tilt as the planet, compared to the system's orbit around the Sun. 

In 1977 a very faint system of rings was discovered, which is of course way beyond reach of amateur telescopes. However, in infrared they appear surprisingly prominent.

During my observation yesterday I was able to make out three of its moons: Titania on the top-left, Oberon on the left and probably Ariel (very faint) nearer to the planet on its bottom-right. Titania is with its diameter of 1,580km the eight-largest moon in our Solar System. Its surface has been dramatically carved in the past and one of its canyons is over 1,600km long, dwarfing the Grand Canyon! Oberon's slightly smaller and contrary to its sister shows little evidence of interaction, apart from being covered in craters. It's also the most distant moon to Uranus. Ariel is number four in size, but usually appears as brightest because of the high reflectivity of its surface. It looks covered in river beds, probably caused by a mixture of liquid ammonia, methane and carbon monoxide that shaped them during the moon's primeval history. There is a lot of water on Ariel but this couldn't have contributed because at the extremely low temperatures on its surface water ice is as hard as steel.

I did "believe" to have seen a sort of darker band on the planet during my observation. At first I wasn't sure if it was real or just the fruit of my imagination after having stared through the binoscope for a considerable time. But when I did some research afterwards, it appeared that the "band" indeed followed the planet's rotational axis as it should have been through my binoscope's view. Therefore the observation may have been correct. I've included a more detailed (and perhaps slightly exaggerated) enlarged inset to give you a better idea.

Uranus lies 19 times further away from the Sun than the Earth, at a distance of 2.9 billion kilometres, and completes its orbit in 84 Earth years. And... no, dear astrology believers, you won't find it in Aries. It's in Pisces at the moment. :-)
 

 

Thursday, 9 November 2017

NGC133, NGC146 and K14: The Cassiopeia Triple Cluster

Everybody knows the glorious Double Cluster in Perseus. In spite of their considerable distance of 7,500 light-years, these two clusters are easily visible to the naked eye and offer an unforgettable spectacle in binoculars or low-power telescopes. Few people are aware, however, that in nearby Cassiopeia you can find a lovely triple cluster, although unlike their famous peers in Perseus its three members are physically unrelated. 

Let's start with NGC133 on the bottom-left (also see the bottom image with labels). It's a fairly poor cluster with only 13 identified members, based on the stars' proper motions and properties. Yet, it's an extremely young cluster with an estimated age of just about ten million years. The bright and hot youngsters are shining at us from a distance of 2,000 light-years.

Next, we movea bit up and towards the centre of the field of view, to find NGC146. Clearly this is a much richer cluster which may contain up to 200 members. The relative faintness of its stars, compared to NGC133, suggests that it lies a lot further away from us, and this is indeed what we find. The average of the various distance measurements places it some 9,300 light-years away from us. Abeit still very young, with an estimated age of 63 million years it's much older than its apparent neighbour. When I come to think of it, this cluster was formed at the time of the cataclism that caused the extinction of the dinosaurs!  

Now let's move down again, and even more towards the centre of the field of view. There lies the most obscure member of the three which doesn't have a New General Catalogue number but just bears the name of its discoverer: King 14. Being the least known of the three, it appeared as the most intriguing and perhaps even the most beautiful of the three, to my humble opinion. Fairly rich and slightly denser than NGC146, it offers a myriad of lanes and structures which are a lovely sight in any telescope. It lies somewhat closer to us as regards to NGC146, with an average estimate of 8,300 light-years. Still considerable I would say. Its estimated age of 32 million years also lies almost halfway between those of NGC133 and NGC146. 

Also note the bright star Kappa Cassiopeiae on the bottom-right. It looks like an ordinary star, just one of millions, barely visible to the naked eye under suburban skies. But what if I tell you that this star still still shines so relatively brightly from a distance of... 4,700 light-years? It looks brighter in our sky from its considerable distance than our Sun would shine from a distance of merely 30 light-years! What if I tell you that this star is one of the heaviest giants known, yielding a whopping 23 solar masses, and that its surface temperature's 4 times hotter than our Sun's? For the moment, this star's still very young, but being such an enormous giant it will burn its fuel in just a few million years and not much after that it will most certainly explode as a supernova!

So here you go. Three clusters and an extroardinary star that have nothing to do with each other whatsoever, but which... as seen from our little corner of out galaxy, make a wonderful sight together.



 

Sunday, 29 October 2017

Abell 72: For those who love a real challenge

I already told you about Abell objects in a recent post and explained that usually they're extremely difficult and even at the limit of large telescopes. Abell 82 is one of the exceptions and even showed some remarkable detail in my binoscope. Number 72 on Abell's list, on the other hand, is another pair of shoes. It's a very difficult planetary nebula that resides in the lovely summer constellation of Delphinus. Its  considerable distance of 4,200 light-years explains its faintness in part, but more important is that this nebula has grown over two and a half light-years in diameter and therefore its feeble light is distributed over a large surface. If you'd like to take on this challenge, approach it with as much aperture as you can get your hands on, low power and an OIII filter to maximise contrast. Did I mention that you're going to need a very good sky too? Well, I guess that was already obvious.

Not a lot is known about this obscure nebula. Given its size, it must be quite old, probably more than 10,000 years, and nearing the end of its existence. Its central star (invisible to me) still appears to be quite hot, at least 100,000°C on its surface, but it's no longer able to fully ionise the enormous gas bubble it ejected and blew up to its current proportions. Soon, interstellar winds will tear the bubble apart and the nebula will completely dissipate into space whereas the remaining white dwarf will extinguish very slowly.  

Look very carefully!

Sunday, 22 October 2017

IC10: Starburst in our Local Group

As I already explained in this post, our Local Group of galaxies has a lot more to offer than the Andromeda and Triangulum galaxies. Actually, its smaller and more obscure members often seem to hide the biggest surprises. IC10 in Cassiopeia is another dwarf galaxy that only recently has been confirmed as a Local Group member. It's a bit larger than Barnard's Galaxy (13,000 light-years across compared to 7,000) and resembles the Large Magellanic Cloud a lot. Unfortunately it lies 2 million light-years away and appearing close to our galaxy's plane a lot of its light is absorbed by interstellar dust. All of this means that it's a challenging object for visual astronomers, as you can also see on my sketch. This is really a pity because IC10 seems to be a mild starburst galaxy, perhaps generating the most active star formation in our Local Group. If it continues at this rate, it will have spent its entire gas supply in the next one to two billion years! 

This radiant activity shows very well on long-exposure photos, where one can identify dozens of star- forming regions. Through the eyepiece of an amateur telescope, on the other hand, this little galaxy only appears as a very faint blob and even with my 18" binoscope I could only imagine a hint of these massive star-forming clouds.

Another interesting feature of this galaxy is that it's enveloped by a huge bubble of hydrogen gas which appears to be rotating in the opposite direction as the galaxy itself!

It's approaching us at 350km/s, which means that it's bound to collide with our Milky Way in 1.7 billion years...

Wednesday, 18 October 2017

IC59 & IC63: The Gamma Cassiopeiae Nebulae

Gamma Cassiopeiae, the middle star of the famous W-shaped constellation, is a hot giant with a surface temperature of 25,000°C (compared to 5,500°C for our Sun) and a mass fifteen times our Sun's. The star shines at us with an incredible luminosity of 40,000 Suns and only looks ordinary from our point of view because it lies at the respectable distance of 610 light-years. It's burning its core hydrogen at an excruciatingly high rate and will most certainly explode as a supernova one day. Already now this star's known as an eruptive variable that may lighten up abruptly to even become the brightest star in its constellation.

Such a big and powerful star must have a tremendous impact on its environment and that's indeed what we find. If you are the proud owner of a ten-inch or larger telescope and have access to a nice and dark sky, point it towards this star and then slightly towards north-east to put Gamma Cassiopeiae just outside of the field of view. This way this bright star will not impair your search for the faint nebulae that surround it too much. These may not be the most spectacular objects you've ever come across and even with my binoscope they were not so easy to detect. But if you try to grasp what it is exactly that you're seeing, you'll surely be impressed. The extreme radiation from Gamma Cassiopeiae is literally tearing neighbouring dust clouds to pieces. The leading edges of these clouds are glowing because of the immense heat and are evaporating as we speak! In a few thousands of years these clouds will have been blown away completely. 


Sunday, 15 October 2017

Abell 82: the miniature Dumbbell

George O. Abell was a famous American astronomer and science professor at UCLA, who became notably renowned for two reasons:

  • His outstanding work combatting superstition, astrology and other forms of pseudoscience, inciting people to embrace reasoning and enlightenment.
  • The catalogue he compiled in the 1950's of over 4,000 astronomical objects, mostly clusters of galaxies but also some faint nebulae.
 
Abell objects are notorious for being incredibly difficult and often at the limit of sizeable telescopes, even under dark skies. However, there are a few exceptions which are also within reach of more modest apertures. One of them is Abell 82, a planetary nebula in Cassiopeia, very close to Caroline's Rose. Don't be fooled, because it remains one of Abell's faint fuzzies and therefore don't expect anything spectacular. That being said, the planetary was quite evident in my binoscope and I was able to distiguish some interesting detail at 190x. Some have described this little nebula as a miniature Dumbbell and I have to agree. Both "wings" of the dumbbell structure were quite visible. 
 
A peculiar thing about this planetary is that no-one still knows for sure where its central star's got to. The reasonably bright star, which appears within the nebula's boundaries, matches a typical central star's hot surface temperature but is too far off-centre to be a suitable candidate. The faint star near the nebula's centre, on the other hand, is a cool K-class star and is therefore most unlikely the culprit. Perhaps this cool star has a close companion that recently kicked the bucket, shedding its atmosphere in the process, but it has yet to be discovered.