Eyes to the monster slayer as we burst through a comet’s tail

This weekend, with a bit of know-how, a dark sky site and help from a handy app, you could be treated to a meteor shower which NASA considers to be the best of the year.

Typically, meteor showers are named after the constellation from which the meteors appear to originate (known as the “radiant”) — in this case, it’s Perseus, the Greek slayer of the mythical Gorgon.

But what makes it #1 on NASA’s meteor shower greatest hits list?

In one word: fireballs.

Along with plentiful beautiful, long-lasting streaks of light, the Perseids are also known for producing much larger explosions called fireballs.

Fireballs are produced when larger pieces of material, including those larger than a metre in size, collide with Earth’s atmosphere and explode. Occasionally, fragments of fireball-causing debris make it to the ground but typically, incoming material is compressed and heated into oblivion in the atmospheric gasses high above our heads.

Map showing fireballs globally
Interactive map plotting globally-reported fireballs over many years. Credit: CNEOS/NASA/Alan B. Chamberlin/JPL

Fireballs often accompany meteor showers occurring as a result of the Earth passing through the ancient debris left over from a visiting comet. In this case, the comet is 109P/Swift-Tuttle and, surprisingly, the connection between the Perseids and this comet has been known since 1865.

Comet 109P Swift-Tuttle orbits every 133 years, last visiting in 1992. So, unless you’re planning on living for a long, long time, this might be the closest you get.

Read More: A fireball with the force of 10 atomic bombs

The other reason the Perseid meteor shower is a sky-watching favourite is simply the sheer number of meteors. The maximum Zenith Hourly Rate (ZHRmax) for this meteor shower at its peak on 13 August is approximately 100. A ZHRmax of 100 means that if the meteor shower was directly overhead, with no light interference at the time of its peak, one could expect to see 100 meteors.

In most cases, though, the shower will not be directly overhead. In the Southern Hemisphere, the radiant will be low above the horizon if it rises at all. For instance, observers in Lima, Peru, can expect the radiant to be around 20° above the horizon due north in the hours before dawn, with viewing prospects capped at around 12 meteors per hour, while the radiant doesn’t rise above the horizon at all for observers in Adelaide, Australia where any visible meteors will appear to rise up from the northern horizon, rather than spray outwards.

The Perseids shower is overwhelmingly best viewed from the Northern Hemisphere. Viewers in London or New York might expect to see 36 meteors per hour or more if they look around two thirds of the way up above the north-eastern horizon just before dawn.

Perseid meteors viewed by a camper with a tent
A camper watches the Perseid meteor shower from Castilla La Mancha, Spain. Credit: Juan Maria Coy Vergara/Getty Images

For all viewers across the globe, this year’s shower will have significant interference from the light of the Moon which is only two days past full and will wash out some of the fainter meteor streaks.

Anyone interested in locating the Perseids or other objects in the night sky might like to check out Stellarium. It’s a free, open-source planetarium application which can be used on your phone or laptop and will help you find your way in the night sky.

Some quick tips for meteor viewing:

  1. Find a dark site, where you can see as much of the sky as possible
  2. Take a blanket or reclining chairs — you will want to be able to relax and not have a sore neck. Leave your binoculars at home.
  3. Rug up and take insect repellent (depending on where you are)
  4. Let your eyes adjust to the darkness for at least 10 minutes
  5. Find the radiant point, but don’t stare here. Look about 30 degrees (that’s just over the distance between your outstretched pinkie and thumb on the sky if you hold your hand out at arm’s length).
  6. Relax, lie back and enjoy the show

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