Spectacular Event “Perseid Meteor Shower”

By Chetan Kachhara | EMN Every year  we witness many eye catching  astronomical events, this year is no exception.  The month of August this year is a treat for stargazers, as  partial lunar eclipse just passed on August 7,  peak Perseid meteor shower going to be on August 12  and a total solar eclipse on August 21. Among all these events,  Perseid meteor shower is creating a buzz in social media and general public with lots of curiosity and doubts. Most of the time the term meteoroids and  meteorites creates confusion and excitement at the same time. The pieces of space rocks before they reach Earth’s atmosphere are known as meteoroids and when they enter the  atmosphere and burn up, they are called as meteors. Some time these meteoroids reaches earth without completely burning up. These fragments of space rocks are known as meteorites. What is Perseid meteor shower? Every year Earth passes through  a trail of debris from the comet Swift-Tuttle.  The comet Swift-Tuttle is periodic comet with an orbital period of 133 years around the Sun. It was discovered independently by  Lewis Swift and H P Tuttle  in July, 1862 and hence the name. The comet made a reappearance in 1992 and it will revisit in the year 2126. As it passes through the inner solar system, it spills out trillion of  cosmic particles and when they enter into Earth’s atmosphere they generate a flash of light called meteor or shooting star.  The streak of light is the trail of burning hot air or glowing material, which meteoroid leaves in its wake.  When meteors occur in clusters, it is known as Meteor Shower. They seem to move in parallel path and with same velocity. They also seem to originate from single point in the sky known as Radiant. According to convention, Meteor Shower are named after the constellation in which the  radiant seems to lie. Some of the common  meteor shower are  Quadrantids, Lyrids, Perseids, Orionids, Leonids etc. The Meteor Shower from the comet  Swift-Tuttle is called Perseids meteor shower because the radiant appear to move away from Perseus constellation in the sky, hence the Perseids. The Perseids happens every year from the middle of July to late August. This year Perseids is visible from July, 17 to August, 27 ( weather permitting). The Perseids is low throughout much of this period. However, it will reach its peak on predawn hours of  August 12 to early morning of 13th as Earth will pass through some of the densest part of stream  of particles of Swift-Tuttle. According to NASA,  Meteor expert Bill Crooke , the Perseids in normal years is about 80 meteors per hour and during outburst year it can go up to 150-200 meteors per hour. This year Perseids  rate will be half of the normal year i.e. around 40-50 meteors per hour due to  presence of  moon. The Moon will rise late  that evening and it will be three quarter full. The fainter trails of meteors will be lost to brightness of  moonlight but the  brighter once should be visible. There is a viral message going around the  social media that there will  be no night on 12th August due to excess light  of meteors shower. This seems to be  little exaggerated. Yes, night sky will be  streaked with meteors (will be difficult to see on cloudy sky ) as they burn in the atmosphere but that does not mean that there will be “no night”. Moon will still rise in the dark night with  Perseid meteor shower. The weather is going to play a big role in this astronomical event as the whole phenomenon depends on whether we will have a clear or a cloudy sky, when that spectacular event takes place i.e meteor shower. (Dr Chetan Kachhara is a professor in Physics at Kohima Science College, Jotsoma)