On its journey around the Sun, the Earth passes through large swathes of cosmic debris. The debris is essentially the remnants of comets — great frigid chunks of matter that leave behind dirty trails of rocks and ice that linger long after the comets themselves have passed. As the Earth wades through this cloud of comet waste, the bits of debris create what appears from the ground to be a fireworks display in the sky — known as a meteor shower.
Several meteor showers can be seen around the year. Among the brightest and best known of them is the Perseid Meteor Shower, which has been active from July 17 onward, and can be seen until August 26. The showers peaked on the night of Monday-Tuesday.
The Perseids occur as the Earth runs into pieces of cosmic debris left behind by the comet Swift-Tuttle. The cloud of debris is about 27 km wide — and at the peak of the display, between 160 and 200 meteors streak through the Earth’s atmosphere every hour as the pieces of debris, travelling at some 2.14 lakh km per hour, burn up a little less than 100 km above the Earth’s surface.
The Perseids currently visible in the night sky are not due to the debris left behind by the comet Swift-Tuttle during its most recent pass, which happened in 1992. This particular comet goes around the Sun once in 133 years, and the meteors now visible were left behind by the pass before the last one — or perhaps even earlier.
Meteors are best seen on a cloudless night, when the entire sky is visible, and when the Moon is not extremely bright. Chances of a successful viewing are higher from locations far away from the lights of cities. Pollution and monsoon clouds make the Perseids difficult to view from India.
The showers peak when the Earth passes through the most dense part of the debris cloud. Peaks can last for a few hours or several nights. They tend to be most visible after midnight and before dawn. The showers should be seen with naked eyes; binoculars and telescopes narrow the field of vision.
According to the International Meteor Organisation, the Perseid Showers will be followed in 2019 by the Orionids (between October 2 and November 7, peaking around October 21-22), the Leonids (from November 6-30, peaking around November 16-17), the Geminids (from December 4-17, peaking around December 13-14), and the Ursids (from December 17-26, peaking around December 21-22).
Inputs from Nasa, The New York Times
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