Perseid Meteor Shower 2021 Brightens The Summer Night Sky

From mid-July to late August, the 2021 Perseid meteor shower put on one of the greatest celestial displays that brightened the summer night sky.

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By Angel Liu

Imagine yourself seated in a rural landscape, gazing at the summer night sky. Out of nowhere, something bright and fiery streaks past your eyes. A few seconds later, more of these streaks zoom overhead. This spectacular display is known as a meteor shower—a celestial event that occurs when the Earth encounters many meteoroids, or small bodies of rock or iron revolving in interplanetary space around the Sun, through the fields of debris shed by passing comets.

Unlike the slightly elliptical orbits of the Earth and most other planets, comets usually have lopsided orbits, with the Sun positioned near one part of their paths. As a comet moves closer to the Sun, its extreme heat causes the comet’s icy surface to melt and vaporize, releasing numerous dust and rock particles into the inner part of our solar system. Therefore, every time the Earth crosses the orbital path of comets during certain times of the year, this cosmic debris collides with our planet’s atmosphere and burns up, resulting in what we commonly refer to as meteor showers, or “shooting stars.”

The Perseid meteor shower, in particular, is perhaps the most beloved summertime classic by skywatchers of all time. Every year between July and August, the Perseids speed toward the Earth at a rate of roughly 133,000 miles per hour and consist of fragments originating from their parent Comet 109P/Swift-Tuttle, a 16-mile-wide periodic comet that orbits the Sun in time intervals of approximately 133 years. Because the debris stream of Swift-Tuttle contains pebble-sized particles that are somewhat larger than those in the debris streams of other comets, the Perseids create much brighter streaks of meteors, called fireballs, as they burn up.

If we were to trace all the trails of any meteor shower backward on a star map, they would all meet at one point: the radiant, a point in the sky where all of the meteors appear to originate from. By tracing all the trails of the Perseid meteors backward, it seems that they hail from the direction of the constellation Perseus—hence the name of the meteor shower—in the northern sky.

Though the peak of the 2021 Perseid meteor shower was predicted to occur on August 12—when the Earth passes through the densest part of the debris stream—the celestial display actually began as soon as the Earth first touched the edge of the meteor stream on July 17 and ended as the Earth exited it on August 24. Throughout these days, the visibility of the meteor shower and the number of Perseids that could be observed varied greatly depending on changes in time, pollution, and the Moon’s activity.

While most individuals prefer watching meteor showers immediately after the sky becomes dark, the best time to view the Perseids is after local midnight in most parts of the United States (or after 11:00 pm where daylight savings time isn’t observed.). Moving closer to 3:00 a.m., even more Perseid meteors can be easily spotted with the naked eye. During this time period, the night side of the Earth will be facing toward the direction of the debris stream, which significantly increases the relative velocity at which the meteoroids collide with our atmosphere, increasing their luminosity, visibility, and abundance.

Besides choosing the right time to view the meteor shower, both light and air pollution play a crucial role in determining whether an area is suitable for skywatching. A 2016 study has shown that 83 percent of the world’s population live under light-polluted skies. In certain areas with extremely high usage of artificial light, 99.5 percent of the stars that people can normally see are completely invisible without optical aids like telescopes or binoculars. As a result, skywatchers located in urban areas may have only been able to observe a few meteors every hour, whereas those who are far away from the cities and suburbs would likely have seen up to 40 Perseids an hour.

Meanwhile, environmental pollutants can also create haze and smoke that wash out fainter meteors from view. John Barentine, director of conservation at the International Dark-Sky Association, and his colleagues have reported that when more aerosol particles are released into the atmosphere, more photons will scatter downward, which will, in turn, increase the brightness of the night sky as seen from the ground. Luckily, thanks to the initial brightness of the Perseids themselves, the meteor shower is visible from anywhere in the Northern Hemisphere and certain parts of the Southern Hemisphere.

Additionally, the Moon has always been one of the biggest concerns in previous meteor shower seasons. The amount of moonlight from different Moon phases can potentially block out dimmer meteors, which poses a common problem during other meteor shower seasons. However, this year’s waxing crescent phase set in the early evening, several hours before the main event begins, providing the best possible dark-sky conditions to allow an exceptionally high number of meteors to be seen by skywatchers all over the world.

With its dazzling fireballs and this year’s moonless sky, the 2021 Perseid meteor shower overcame several hindrances that would otherwise prevent such a remarkable display from being observed. If you had the chance to sit down in your backyard and watch the Perseids “rain” for more than just a few minutes, it was undoubtedly a once-in-a-lifetime memory to be kept for years to come.