Its time for a starcast again.
As we approach the Autumn equinox, the Milky way is in the best position to see the full extent of the arm of our galaxy, that is visible to us.
The solar system is located in an outer arm of the Milky Way, which is a spiral galaxy. Its about 100 000 light years across, and we are located about 25 000 light years from the galactic centre, where a supermassive black hole’s gravity keeps everything in place, as we rotate around the galactic core at 250 km per second.
Apart from a few exceptions, most of what we observe looking up at the band of the Milky Way is within 8000 light years. The centre of the galaxy is located in the Sagittarius constellation, but is not visible, obscured by dust and other material
concentrated along the galactic plane. If you visit Darkskyes we’ll tell you alot more about this.
So, turn to face south.
Starting on the the south east horizon you should see the Milky Way stretching up, overhead and becoming fainter as it drops onto the north west horizon.
The first two prominent stars you see are the pointers, located in Centaurus. The lower star is Alpha Centauri, the closest visible star to us at 4.3 light years. Although it appears similar, the higher pointer, Hadar is a triple star system located nearly 400 light years away.
Now move up into the well known southern cross asterism, located in Crux, the smallest constellation in the night sky.
The brightest A Crux is a triple star located about 320 light years away. Within the cross you can see a dark patch, known as the Coalsack nebula. Using binoculars, try and find the tiny Jewelbox cluster, just adjacent to the second brightest star in the cross. While it looks similar in distance, this cluster is over 6000 light years away.
Now point your binoculars higher along the galactic plane, into a dense region of stars. You’re now in the constellation Carina, and without much difficulty you should find the Carina Nebula, illuminated by the star Eta Carina. The constellation is very dense and you can see a number of clusters including the spectacular Southern Pleiades (not to be confused with the Pleiades).
Now move higher up into the constellation
Vela, where you find another asterism- the False Cross, which bears a poor resemblance to the Southern Cross, and had early seafarers from the north confused as they ventured south.
Another asterism – the Diamond Cross, is also also located in the same area.
You should be craning your neck now, moving even higher into the constellation Puppis.
Almost directly overhead is the constellation Canis Major, marked by the brightest star in the night sky (Sirius). It is also relatively close, at about 8 light years. Look for what I call the “armchair” just to the south of Sirius. The two main stars of this little asterism are Adhara and Wezen. You will notice that Adhara has a distinct blue hue. This is not surprising, as it is the brightest source of ultraviolet light in the night sky, with a surface temperature of
over 25000 degrees c.
Unless you are an experienced Yogaist, you should now have turned to face north. The next constellation in line is Orion. Look at the bright orange hue of Betelgeuse (bottomish right) and compare to the blue of Rigel ( top left) The nebulosity in the centre of Orion (The belt and sword) is clearly visible even in binoculars. This is an area of current intense star formation.
Now, move down towards the northern horizon, into the constellation Taurus, where the head and horns of the bull are clearly visible, marked by the giant bright orange star Aldebaran, located about 65 light years away.
Even closer to the northern horizon you end your tour of the Milky Way at the Pleiades ( seven sisters), still in Taurus.
You could also just visit Darkskyes, and get all this handed to you on a plate, along with a bowl of creamy butternut soup and crunchy croutons. Check the Darkskyes website ( www.darkskyes.co.za) for best viewing times.
Darkskyes out.