Tuesday, 20 December 2011

It is that time of year again

Now we come to the Christmas break where other things get in the way of blogging time.

I will be back in the New Year, have a good one.

Tuesday, 13 December 2011

When I were a lad.... 3

A magical moment

Something I saw recently reminded me of an incident from my childhood.  It happened in the winter of 1956 / 1957.  At that time we lived in a small house in a village close to London, an area now a part of Greater London but then it was in Hertfordshire.  Our house was on the side of a small hill and was built on quite a steep slope with a metalled drive running beside the house which led to my father's small business, a Garage where he eked a living repairing cars and selling petrol. 
That night I was sound asleep in bed when Dad came upstairs and woke me up, made me get wrapped up warm and without saying why, he took me out into the winter night.  I don't know what time it was but it must have been late.  We stood on the sloping driveway facing north and when my eyes had adjusted to the dark, high in the Northern sky was the most amazing comet I have ever seen, indeed the first comet I had ever seen. It stretched almost vertically up the sky, tail up just like the images in all the books. That was the only night it was visible at that majestic stage in its path around the sun, because there were clouds for weeks before and after. Although I did not know it at the time, it would have been the Arend - Roland comet which was discovered in November 56 and peaked early in 1957. It came quite close for a comet, within half the distance that the Earth is from the sun, (0.5 AUs) and was quite bright at its peak. 
Many years later in 1997, the brightest comet since then that I saw was the Hale - Bopp comet, which whilst visible for much longer, was disappointing to me because I was expecting to see something more like the Arend - Roland comet.  
The Arend – Roland comet was much more like a comet should be, whilst the Hale – Bopp was much smaller, fuzzier and split into two tails. 
In the intervening fourty odd years, sky photography has improved in leaps and bounds, so the images you can see now are not comparable, but the real thing was magical.
The Arend - Roland comet 1956/57
The Hale - Bopp comet 1997
For those who like to know things, the distance I put in brackets, 0.5AU, is half an Astronomical Unit.  Astronomers think in big numbers, literally astronomically big numbers, so miles or kilometres are much too titchy to use because they will give you great long strings of figures.  An astronomical Unit is the mean distance from the Earth to the Sun and is a useful size for interplanetary distances within our solar system.  It is almost 93 million miles or to be exact, 92 955 887.6miles
For measuring distances between stars, another unit is used, because AUs are much too small for those kinds of distances and although the term Light Year is often used in news reports and movies, real astronomers tend to use the Parsec.
The Parsec is rather complicated as to how it was derived, so I won't bother with that, but it is just over three and a quarter light years and makes a much more useful unit of distance for Astronomers to use between stars, since the nearest star Proxima Centuri is a little over one parsec from us. For even greater distances, the kiloparsec or the megaparsec are used and now we are tlking inter Galactic distances which are turly big.
Ok so a light year?  
 On TV news broadcasts, when the roving reporters are linked to the news desk via satellite, you notice they stand and nod their heads idiotically for a few seconds before replying to the person in the studio. This is because they have not heard the person in the studio yet and although satellites are only a mere 20,000 or so miles high, it takes the TV signal, travelling at the speed of light, a few seconds to go up and bounce down again. It takes the light from the sun just over four minutes to reach us and that is only one AU. It takes over four years to reach Proxima Centuri which is the closest star.  If news reporters ever get to Proxima Centuri, the news will be over four years old by the time it reaches us and any conversation would take near enough nine years to get a reply. So a light year is one damned long way, well 5,878,499,810,000 miles to be exact and since a Parsec is 3.26163626 Light Years, we are talking big big number in miles or kilometres and very very very long distances.