March 2010

The long summer nights in the Cape also mean many evenings with clear skies for skygazing. The area around Orion dominates the view all summer and this year it has been particularly rewarding to follow the movement of the beautiful reddish glowing planet Mars nearby.

But what I find even more exciting is the view to the South, where the beautiful Southern jewels invite you to inspect them more closely. Provided you have escaped the worst of the city lights, that view to the South also includes the two Magellanic Clouds with the popular attractions of sights such as the Tarantula Nebula (NGC 2070) in the LMC or the beautiful globular cluster NGC 104 (47 Tucanae).

I am fascinated by those two neighbouring galaxies. They are not the closest galaxies to the Milky Way (we know that at least the Sagittarius Dwarf Spheroidal galaxy and Canis Major Dwarf Galaxy are closer), but we here in the South are lucky to see our such close neighbours of our home galaxy so clearly. Exploring their beauty and their interesting features through a telescope or even just binoculars is always rewarding. But mostly they interest me because they make some of the concepts relating to distant galaxies somewhat easier to comprehend. Thinking of them as objects that are really far away in human terms (160 000 light years and 200 000 light years respectively away from us and roughly 75 000 light years away from one another), yet very close in cosmic terms, gives me a starting point to start reflecting about distances and time scales in the universe. The LMC is the 4th largest galaxy in the Local Group after the M31 (the Andromeda), the Milky Way and M33 (the Triangulum Galaxy). They are considerably smaller than the Milky Way (the LMC is about about 1/10 that of the Milky Way), but even so they stretch human imagination and concepts of quantities and distance.

Although the LMC has always been classified as an irregular galaxy, recent photographs of the LMC clearly show its large central bar and one spiral arm – leading to some theories about its possible shape in the past as a barred spiral prior to its tidal interaction with the Milky Way and probably the SMC as well. On closer inspection, the SMC also shows a large central bar structure and again one can speculate about its earlier structure.

The largest brother in our Local group – the Andromeda - is about 2.5 million light years away and contains as many as a trillion stars. Nevertheless, recent studies have shown it may be no more massive than the Milky Way since our own galaxy seems to contain more dark matter than M31. It always gives me a thrill to find it – just like the Magellanic Clouds, it gives me an instant indication of how dark the area is from where I am observing (provided it is the right time of year and night to see it clearly). It is invisible by naked eye or binoculars from my light-polluted suburban home, even though I know exactly where it is. However in some darker areas of the Cape Town metropolitan area I can pick it out quite easily without optical aids.

These thoughts about our galactic neighbours take me to the wider topic of galaxies. My interest in their classification and larger groupings, goes back a long way and I was particularly excited when members of he public all over the world were given the opportunity to participate in a galaxy classification project through Galaxy Zoo (see notes). I jumped at the opportunity and have learnt a great deal. Being involved in such a project keeps one’s interest alive - among others through discussions with other participants.

Galaxies are the “towns” and cities of the universe. Some of them merge into large cosmic metropolitan areas. Some have a mainly ageing population of stars, some abound with new stars being born. Human cities mimic the way in which galaxies change shape - or perhaps we humans prefer to think of it the other way round. We even use similar words like “lanes”, “population” and others to describe features of galaxies.

They seemingly float in the cosmic void and it is no wonder that a popular description of galaxies has been that of “island universes”. They stretch the imagination and our thoughts while also being popular and rewarding skygazing objects. Anyone who has tried to see all of the visible Messier objects (not all are visible in the Southern Hemisphere) or who is working through a particular area of the sky to find all its most notable objects, can attest to the fact that some galaxies are much more challenging to find than others. It can indeed be downright frustrating to find some of them – spotting a little smudge in our eyepiece that has been eluding us, but that our star charts tell us should be there, becomes a mini triumph.

I admire the astro-photographers who manage to capture the beauty of galaxies. It takes a lot of skill (and the right equipment) to come up with some of those stunning shots that we can see in books, magazines and on the Internet. Some people spend a lifetime of lonely vigils at night hardly noticing the more obvious and “common” sights of nebulae and star clusters in our own galaxy – but night after night they turn their light buckets towards those areas where the fainter galaxies can be found – and some of them are so good at this that they can find some faint fuzzy almost as quickly as we can find the great nebula in Orion. I admire those guys for whom even the more difficult Messier objects are no longer a challenge and who need more detailed astronomical charts to find their targets.

For some of us those little faint smudges are a bit boring. But when one thinks that such an object is something hundreds of thousands and even millions of light years away and contains maybe as many or more stars than our own galaxy, then even a glance at something faint and fuzzy that blinks in and out of view as Earth’s atmosphere interferes with your viewing, is an awesome moment. We are looking at something really big and far away that may contain stars housing sentient beings - but even more awesome is the thought that you are looking so far back into history that the light from that object may have left even before the dinosaurs roaming the Earth. You need about an 20-inch light bucket to see the faint galaxies in the Coma cluster of galaxies - small wonder because they are on average about 320 million light years away. Compare this with the fact that the dinosaurs lived on Earth from about 245 million years ago for about 180 million years – their extinction predating humans by more than 60 million years. Most of us have smaller telescopes and have to concentrate on closer targets in the Virgo cluster, Leo or other galaxy-rich areas of the sky. Nevertheless those are also pretty far away at about 60 million and 38 million light years away respectively.

Large research telescopes probe the universe much further than that and indeed has looked back to a time when the universe was only about 3 percent of its current age. Now that’s a thought to ponder next time you look up at those lovely Clouds in the South…


Notes:
• Galaxy Zoo: find it at www.galaxyzoo.com. You have to register and undergo a quick online training process before you can start helping with the classification. Galaxy Zoo 2 concentrates on galactic mergers.
• A separate, but equally interesting Galaxy Zoo project looks for supernovae at http://supernova.galaxyzoo.org/
• For those more interested in stars, and in particular our Sun and its more violent moments, the Zoo Universe team also recently started a “sister” project to help look for solar storms Find that at http://solarstormwatch.com
• For those who are interested in some recent discussions about galaxies, especially some recent ideas about spiral galaxies have a look at the S&T website: http://www.skyandtelescope.com/news/84476312.html?imw=Y

(Written originally for the newsletter of the Cape Astronomical Society of Southern Africa)