Just that I thought I could share my take on this…especially bearing in mind the fact that we have a few of these coming in the next month or so..
Nothing as fascinating as seeing a bright streaker zoom across the sky…only gets more fascinating if your lucky stars do bring you some luck and you be probably able to get one of the really brighter streakers ( I’ve heard of ones that last 20 secs + ) …Ofcourse It would have to be a special day if we can catch a fireball…But again we’re venturing into the realms of a meteor shower that would be more of a fantasy than reality.
So.. We all know that meteor showers are due to the debris left behind by periodic comets and they occur whenever the earth passes through that part of the orbit where these are.. And that we recognise meteor showers on the basis of which comet the debris or the meteoroids causing these showers belong to…and ofcourse which constellation they seem to come from… The Leonids , Peresids , Geminids being the more famous ones of the showers..although there are the lesser potent ones in ursids , aurigids , orionids , eta aquarids , lyrids and many more..
What not a lot of people don’t have a proper idea is about how these really happen..how they light up in the atmosphere..how far up they’re getting lighted up and how far down do they make it.
How a meteoroid will behave when it enters the atmosphere depends on three factors basically – the composition , speed and angle of entry of the same..Generally the faster the meteor and the oblique the angle of entry – the brighter it is.. Even the High-Iron meteors that tend to withstand enoromous stresses burn out when the atmosphere gets thicker. Contrary to most people’s understanding of why meteors light up ..the obvious reckoning being that it’s because of friction …is a misconception… It’s something similar to what happens in a Diesel engine – The meteoroid compresses the air in front of it ..which ofcourse heats up the air..and the heated up air in turn causes the meteoroid to burn away.
This is the concept of Ram Pressure – ofcourse the name itself intended to be synonymous to the action of a battering ram. A peculiar , obnoxious yet amazing concept ..A meteoroid being capable of compressing air. Don’t mistake this to be the same as friction – where heat is produced primarily due to the rubbing of air molecules on the meteoroid. The Ram pressure concept has far bigger implications in stellar astrophysics of star and galaxy formations. Anybody with proper conceptual understanding of fluid mechanics will probably get a better hang of this thing.
Then there are the more sore spectacular versions of these – the fireballs. While most meteors seem to streak past – burning approximately at about 60km up – there are these larger ones that splatter as they burn .. causing a brilliant flash of light and streaks that last several seconds…and accompanied by explosions that can sometimes be heard. You’d be lucky if you can catch one of these.
And then there are the scary versions of these as well.. The unusually big ones that penetrate through the atmosphere and explode just above or on the surface.. These have been known to cause disasters , alter landscapes and geography. The most recent incident being the one in siberia – early in the 1900s.
It’s been estimated that meteorites cause craters 12-20 times their size – this after a traumatic penetration through the atmosphere where their speed was taken to have reduced to half of that on entry. Doesn’t take much explaining on the magnitude of havoc a big one can cause.
Just a few instances of meteorites in the past
-> A meteorite impact wiped out hundreds of square miles of forest area in siberia – June 30th 1908. Witnesses of this Tunguska event claim they saw a ball of fire streak through the city..all suggesting that it could’ve been a meteor entering at a very oblique angle. The explosion caused was powerful enough to cause hot winds and loud noises that were off such magnitude that they broke glass windows in the vicinity. Amazingly enough ..No meteorite or an impact crater was found. Since then. there’ve been various speculations about this ( amar had suggested in his seminar that he had read somewhere that this was due to a passing black hole ). We now know that this was because of a meteoroid that explodes just above the surface.
-> The Arizona crater – it’s rims rising 150 ft from the surrounding plain , a hole 600 ft and nearly a mile wide is the result of a meteorite impact that occured more than 20,000 years ago.
Getting back where we were – We have a few meteor showers coming up this season – To start it off – The Orionids – which’re generally faint and average about 20 per hour followed by the Aurigids which’re about the same – Followed by the Leonids – Rate exceeding hundred every hour and a few bright streakers as well.. And ofcourse the best of all being the Geminids – putting up their show in December .. Averaging about 80-100 streakers per hour and most of these being bright ones at that.
A busy season ahead for the BAS .. Will be relaxing , less hectic and pure fun for all you people who’re not much into deep sky observing as some of us others are.. A very simple thing to do after all.. Just the fact that it takes no more than you coming with us to Hosahalli .. and probably getting along for yourself .. a couple of blankets. Just lie down and keep your eyes open .. you might be in for a bright one .. Then ofcourse .. you can catch 40 winks in the process and dream about one of them meteorites landing next to you.
Clear skies and bright meteor showers