Monday, August 5, 2013

Fire from the skies 
(in monsoon!!)

Perseids Meteor Shower
Seeing a shooting star in the sky makes one feel that a star has died, but is it really so. Death of a star results in one of the biggest celestial shows in the universe and definitely a shooting star is not that. The words “shooting star” itself is a misnomer. We all know that when a small particle of space dust enters earth atmosphere, it burns up while travelling towards Earth and result is a streak of light in the skies. It has nothing to with star death. Sometimes the particle is so big that part of it burns in the atmosphere and the rest falls on earth.

Meteor observers will finally be breaking out of their slowest time of the year when the Perseids meteor shower peaks on the night of August 11/12th 2013.

The Perseids are a prolific meteor shower associated with the comet Swift-Tuttle. The Perseids are so-called because the point from which they appear to come, called the radiant, lies in the constellation Perseus. The name derives in part from the word Perseides (Περσείδες), a term found in Greek mythology referring to the sons of Perseus.

The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift-Tuttle. The cloud consists of particles ejected by the comet as it travels on its 130-year orbit. Most of the dust in the cloud today is around a thousand years old. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1865.The rate of meteors originating from this filament is much higher than for the older part of the stream.

The Perseid meteor shower has been observed for about 2000 years, with the earliest information on this meteor shower coming from the Far East.Some Catholics refer to the Perseids as the "tears of St. Lawrence", since 10 August is the date of that saint's martyrdom.
What is a meteor and a meteor shower?
Does it mean that when meteor shower occurs we expect fireballs from the skies falling on earth, or does it actually look like shower of meteors? Let’s find out the facts one by one. As mentioned earlier a meteor is “A meteor is the visible path of a meteoroid (a small sand size particle) that enters the Earth's atmosphere, commonly called a shooting star or falling star. These shooting stars can be seen on any night and they fall at random. But when the number of meteors is large, it is called a meteor shower or meteor storm. The shower always happen on a particular day or a time period as it is associated usually with comets. During meteor showers (which usually last a few days), the majority of the meteors appear to come from a particular point in the sky, called the radiant of the shower. The meteor shower is commonly named after the constellation in which this

radiant is found, and occurs annually during a well-defined time period. For example, the Perseid meteor shower occurs every year from about July 25th through August 18th, with a peak on August 12, and has its radiant in the constellation Perseus. In this shower, the typical maximum number of meteors that can be seen per hour at its peak is about 70, which is 10 times the rate of random meteors. Now how or why this shower occurs? As comets move about their orbits they leave a stream of debris because dust and rocky material is liberated from the head as the ices vaporize. If the earth crosses the cometary orbit, this debris leads to an increased number of meteors
The Perseids are the most famous of all meteor showers and never fail to provide an impressive display. Records of Perseid activity go back to 36 AD. In 1839, Eduard Heis was the first observer to take a meteor count and discovered the Perseids had a maximum rate of around 160 per hour. Other observers have since continued these studies to find the fall rate varies considerably. Astronomer Giovanni Schiaparelli was the first to relate the orbit of the Perseids to periodic comet Swift-Tuttle.
How does one see the meteors?
Meteors generally appear as streaks of light in the sky, appearing javelin-shaped. They will typically last only a fraction of a second and will be about as bright as most stars. Brighter meteors will occasionally appear, very roughly about one every ten meteors, which will usually be brighter than any star. They will usually last less than a second.
The brightest meteors are often termed fireballs, which will appear like brighter meteors, except will be brighter still. These often fragment as the pass through the atmosphere and glow a brilliant green. These brightest of meteors are often claimed to be UFO sightings
The show
The Perseid meteors will streak across the short summer nights – August 10-13 – from late night until dawn, with little to no interference from the waxing crescent moon. Plus the moon will be near the planet Saturn in the evening hours, giving a colorful prelude to late-night Perseid show. 

Best mornings to look: August 11, 12 and 13. 

It will peak on the night of 12th August 2013, Best time to observe is to watch late night/early morning when the Moon has already gone down the horizon. Showtime usually begins as soon as the radiant (near the Double Cluster in Perseus) clears the horizon, an hour or so before midnight, and it climbs higher in the sky throughout the night. This should be a great year for the Perseids, because a fat crescent Moon should be setting just when the shower is starting to increase.
Only problem would be the clouds as we have the Monsoon season here.

When Perseus rises in the northeast. This is the time to look for Perseid Earthgrazers--meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping the surface of a pond. Earthgrazers are long, slow and colourful; they are among the most beautiful of meteors. An hour of watching may show only a few of these--"at most"--but seeing even one makes the long night worthwhile. The thin, crescent moon will be out of the way early, setting the stage for a potentially spectacular show. For best viewing, look to the northeast after midnight. Other things which will spoil the show will be monsoon clouds.
How to observe the meteor shower?
Don’t expect hundreds of meteors in the skies at one time. Perseids meteor shower usually have ZHR of around 100-120 meteors. Now what is this term ZHR? Official figures for meteor numbers are given as the ZHR or Zenithal Hourly Rate. This is the number of meteors you could expect to see given perfect conditions if the radiant (the point from where all the meteors seem to be coming) was directly overhead - i.e. at the zenith. Obviously, if the radiant is on the horizon, you can't see half the sky around the radiant, so you will only see half the number of meteors. Again, if half the sky is cloudy, you will only see half the number of meteors. Hence, for a ZHR of 110 (about what you can expect for the Perseids shower), you might only see two-thirds or half because the radiant isn't directly above your head. So expect to see around a meteor per 2 minutes !!
The first and last rule of meteor observing is look up. If you do not look up, you will not see any meteors, because by the time someone else has seen it, it will be gone before you look in that direction. Rules for meteor observing are generally the same as for all astronomy observations. The exception to that rule is that you should be looking up at all times. You can employ an easy chair for this purpose, but the best way is to get a sleeping bag and find a dry, comfortable spot to lie down on.
For observation make sure that you have the widest area of sky visible possible. Try to get away from light pollution. If you can see the Milky Way, it will be dark enough to see meteors. Typically, meteors will be about the same brightness as Venus or Jupiter down to the brightness of medium-brightness stars).

Depending on your location and disposition, insect repellent like odomos gel might be advisable as well. On the whole, just use common sense and try to enjoy yourself. Meteors can provide some of the more spectacular sights in the sky, so stop reading about it and get out there!

No comments:

Post a Comment