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... :-)