Fleeting moments - astronomically speaking

The fireball seen in the Northern parts of South Africa the country late last year prompted me to ponder about our fragile planet being hit by objects from space. However, it also made me think about the thrill and lasting impressions of some fleeting moments relating to astronomy.

There is the “everyday” beauty of moments of unexpected delight: a full moon that suddenly rises from behind buildings or a mountain like a butter-coloured yellow balloon against a navy-blue early evening sky. Or the pleasant surprise of looking up from the centre of a light-polluted city on a very clear evening - and realising that I could easily count six of the Seven Sisters in the Pleiades. Or watching the stars pop out one by one as you sit at the beachfront and having a stranger come up to you to ask if they may borrow your binoculars for a moment to look at Jupiter or Saturn.


But there are some more dramatic, less “everyday” fleeting moments of seeing some rare or uncommon events. Eclipses, transits and occultations come to mind immediately as predictable, but rare phenomena that are exciting, interesting and beautiful. Careful observations and timing relating to these phenomena (often by dedicated amateurs) provide useful data and help the professionals to understand more about the Sun and the Solar System.

But even if you are not doing it for science, simply looking at these events and perhaps photographing them, can be a rewarding and memorable experience.

The totality phase of a total solar eclipses lasts only a few minutes, yet people often pay large amounts of money and travel far to see these events. Partial solar eclipses and lunar eclipses are also beautiful, but those rare, full eclipses are something special. Many – probably most - of us never experience the thrill of those few minutes of “seeing it with our own eyes”, and have to live vicariously through other people’s stories and pictures, pod casts, television broadcasts and other electronic meansSimilarly, the rare occurrences of transits of Venus and Mercury are eagerly-anticipated events. Do you remember how excited we all were in 2004 to watch the black dot of Venus slowly moving across the face of the sun? I luckily thought of holding my camera to the eyepiece of the 7-inch telescope at the SAAO on that occasion, and took a photograph through the same telescope that was also used here in the Cape during the observations of the 1882 transit of Venus (the Mertz is now mounted as finder telescope to the 18-inch Cox-Hargreaves Telescope).

In case you were wondering, the next transit of Venus will be on 6 June 2012, while the next transits of Mercury take place on 9 May 2016 and on 11 November 2019. Mark the dates on your long-term calendars and hope for clear skies…

Then there are occultations: not all of us are interested in, or know how to observe occultations of stars. However, events involving the moon and planets are (relatively!) more common, even though you still have to be at the right place at the right time to observe them. Who remembers that stunning occultation of Venus by the moon on 20 January 2007 while, in the same breathtaking panoramic view shortly after sunset, Comet McNaught blazed over Table Bay and Table Mountain? Many people catch the astronomy bug by a sight like that.

But there are rarer events of transits and occultations in the solar system still, such as when one planet moves in front of another as seen from Earth. When is the next one? Well, many of us will no longer be around when it happens: on November 22, 2065 Venus will transit in front of Jupiter. The previous time it happened was long before any of us was around - on 3 January 1818 when Venus also transited Jupiter. Double occultations (when two or more planets are very close to one another as seen from Earth and when the moon then occults them both) are also very rare. Observers on Ascension Island were correctly situated on April 23, 1998 when the moon occulted Venus and Jupiter simultaneously.

Fleeting moments come in other shapes as well. It may be stretching the meaning of the word to call observing a comet a special “moment” – but these visits by objects from far away in the Solar System are nevertheless memorable at least in part because they are relatively brief. Of course there are very many comets and you can have a look at the latest discoveries on the website of SOHO and elsewhere. But for the greater part they are faint and not easy to observe. Indeed most of them are fairly unremarkable and seldom hit the headlines. Few people see repeated visits (Halley is the often-referred to example with its 76-year period) of the same “great” comet that gets the world talking.

Comets that are easily visible with the naked eye are fairly rare and the really great ones rarer still. By definition long-period comets visit our part of the solar system only once every 200 years or more. Some comets break up dramatically and cause spectacular sights such as the demise of Comet Schumaker-Levy when it broke apart and its pieces collided with Jupiter. Some comets are little more than a faint blob in your eyepiece or through binoculars. Others reward you with their subtely changing shape over a period of weeks as it travels around the Sun. Some make for great pictures for those who know how to photograph them. But then there are those that truly make you catch your breath and become a defining moment, such as the visit of the non-periodic Great Comet of 2007 (McNaught C/2006 P1).

Watching a meteor shower, or spotting a meteor when you are casually looking up or during an evening of stargazing, is great fun. Some of us are even disciplined enough to make notes and forward those observations to the Comet and Meteor Section of ASSA. But the more poetic side of our nature will admit that we at least once wished upon a shooting star – or told someone to “quick, make a wish!”

There are many other fleeting moments that contribute to the magic of the night sky and live in our memories. For me one of those was when I saw a green flash from Sutherland years ago. The strange thing was, on that particular evening a friend and I specially went outside to look for it – and I was really skeptical about the possibility. My expert friend had seen it there a few times and nature played along: just as he said, “Wait, any moment now, but don’t you dare blink!”, there it was! A definite flash, rising from the horizon for “one brief, shining moment” (to quote the lyrics from Camelot completey out of context). Green. And very memorable. I keep watching the horizon at sunset whenever I can, but the next one is still eluding me. A pretty flash of light immediately after sunset is something that most people would say is not really worth worrying about, but I’m glad I’ve seen our home star wink at me through the Earth’s atmosphere in that way at least once.

Isn’t astronomy wonderful? It fascinates you for a lifetime – and yet some of its most memorable moments come and are gone like a beautiful melody that you hear once and never again.

(The picture illustrating the first part of this entry is the one I mention which was taken during the the transit of Venus through the old 7-inch telescope at the SAAO.  Pictured here is that telescope in its piggyback role with people looking through it on that day.)