## Wednesday, April 4, 2012

### Southern Winter Milky Way Skies.

Today I want to do something a little different and share a picture taken by my housemate and good friend Jonathan. He's recently gotten into astrophotography using his DSLR camera, but has been too busy to do much (it being his last semester at UHHilo and all).

Two weeks ago he was able to make it up to the Vis and took the following picture, which he posted on his blog (which you can find at Life is a Zwitterion). I saw it and offered to label the constellations and a few other objects visible in it for him, and he suggested I post it on my blog, so here it it. Thanks Jon!

This is a 30-second exposure taken from the Visitor Information Station on Mauna Kea looking south at 8:25 on March 19th, 2012. Visible near the bottom is the flank of Mauna Loa, with part of the rim of Puʻu Kalepeamoa visible in the foreground (ka lepe a moa means "the comb of the rooster" in Hawaiian, which is  an apt description for the shape of the range of hills it is part of). In the background lies a stretch of the winter Milky Way, with several prominent constellations visible.

Also visible in this picture are the two brightest stars in the night sky, Sirius and Canopus. Sirius is one of the twenty closest stars us, a mere 8.6 light-years away. It is actually a binary system composed of a white main sequence star (Sirius A) of spectral type A1 about twice as massive as the Sun and about 25 times as luminous, and a white dwarf (Sirius B) first discovered in 1862. Sirius B has a diameter of about 12,000 kilometers (7,500 miles), nearly the same as Earth, but contains 98% of the mass of the Sun.

The other bright star, Canopus, is much further away: 310$$\pm$$10 light-years. Canopus is a supergiant star of spectral type F, and it is 13,600 times more luminous than the Sun. In fact, it's the most intrinsically luminous star within ~700 light-years. Unfortunately, it's far enough south as not to be visible from much of the continental United States, although south of 37$$^\circ$$18' it may be visible under very good conditions.  Its radius is fully one-third of the distance from the Earth to the Sun, about 50 million kilometers or 30 million miles.

Along with stars, there are quite a few constellations (or parts of them) visible in this image. Prominently placed is Canis Major, the Big Dog (Canis Minor is out of the top of the picture, however). The three constellations that made up the old constellation Argo Navis are also visible here; Puppis, the Poop Deck, Carina, the Keel, and Vela, the Sail. Also visible is Pyxis, the Ship's Compass, though it is a modern addition by Nicolas Louis de Lacaille in the 18th century. Below Canis Major is Columba, the Dove, and Pictor, short for Equuleus Pictoris the Painter's Easel (another modern addition courtesy of de Lacaille). Finally, just at the bottom of the picture is Dorado, the Swordfish. Dorado is interesting because it contains both the majority of the Large Magellanic Cloud (one of the Milky Way's satellite galaxies) and the south celestial pole. In fact, if it weren't for Mauna Loa getting in the way, the Large Magellanic Cloud would be visible at the bottom of the picture.

Finally, there are at least three Messier objects visible in this picture (there are probably even more that I missed): M46, M47, and M41. Messier 46 you may recall as the open cluster with superimposed planetary nebula I showed a picture of a few weeks ago.