Meteor shower in Wincrange / © Adriano Anfuso
Every year, observers around the world turn their eyes to the night sky to catch a glimpse of meteor showers, some of the most accessible astronomical events, requiring no telescope or special equipment, just a clear view of the sky, ideally far from city lights.
But what causes meteor showers? Why do they return at the same time each year? And what exactly are we witnessing when one streaks across the sky?
Let's start with a few key definitions. A meteoroid is a small fragment of rock or metal travelling through space, usually originating from a comet. Most are less than a metre across. When a meteoroid enters Earth's atmosphere at high speed and burns up due to friction with air molecules, we see a bright streak of light known as a meteor.
If any part of the meteoroid survives its fiery passage and reaches the ground, it becomes a meteorite. Occasionally, a meteor is exceptionally bright, often outshining Venus and sometimes exploding mid-air. These are called fireballs or "bolides" and can sometimes produce sonic booms or break into fragments as they fall.
Meteor showers occur when Earth passes through a stream of debris left behind by a comet, or occasionally by an asteroid. As a comet travels around the Sun, solar radiation causes its surface to heat up and vaporise, releasing dust and small rocky fragments. These particles remain scattered along the comet's orbital path, forming a long, dense trail of debris.
Venus and a meteor shower in Clervaux / © Adriano Anfuso
When Earth's orbit crosses this trail, some of the particles enter our atmosphere at incredible speeds, between 11 and over 70 kilometres per second, creating the bright trails we recognise as meteors.
Because the debris trail left by a comet remains along its orbital path, Earth encounters these streams at roughly the same time each year. This regularity gives meteor showers their seasonal nature, making them predictable to skywatchers.
Among the most popular recurrent meteor showers is the Perseid, with its peak during the warm, clear mid-August nights, as Earth crosses the dust trail of Comet Swift-Tuttle. The Leonids, by contrast, appear in mid-November and originate from Comet Tempel-Tuttle. Then there are the Quadrantids, active in early January, which are linked to the asteroid 2003 EH1, thought to be the remnant of a long-extinct comet.
Of course, not every meteor belongs to a recognised shower. On any given night, it's possible to spot sporadic meteors, isolated meteoroids entering Earth's atmosphere from random directions. These may be fragments of old, dispersed streams or stray bits of interplanetary dust not linked to any comet. Unlike meteor showers, they don't appear to originate from a specific point in the sky and are not recurrent.
Furthermore, not all meteors look the same in the sky. Some display striking colours as they burn up in the atmosphere. These colours reveal important clues about their chemical composition as different elements emit light at specific wavelengths: sodium produces a bright yellow glow, magnesium appears blue-white, iron shines orange, and calcium gives off violet tones. The oxygen in the atmosphere can also contribute with green or reddish hues. By studying these colours, scientists can identify the elements present in the meteoroid and better understand its origin.
© Adriano Anfuso
Meteor showers also vary in characteristics such as speed, brightness, and frequency, that is, the number of meteors visible per hour. These differences depend on the velocity and composition of the original stream of debris left by the parent comet or asteroid.
Scientists study meteors to learn more about the composition of cometary material and the long-term behaviour of meteoroid streams. By analysing how these particles interact with the upper atmosphere, researchers gain insights into the physical properties of the dust and how the streams evolve over time.
A key feature of meteor showers is the radiant, the point in the sky from which the meteors appear to emerge. This is a trick of perspective: although the meteoroids in a stream travel on parallel paths, to an observer on Earth they seem to converge towards a single point, much like railway tracks meeting at the horizon.
Knowing the location of the radiant helps observers figure out which meteors belong to a particular shower, and it's also essential for planning a proper night of observation. Once you know where in the sky to look, all you really need is the shower's peak time and a favourable location.
Several factors can influence what you see. First, the time of night matters: after midnight, your side of the Earth is facing into the direction of our planet's orbital motion, which increases the number of meteoroids entering the atmosphere. That means more meteors to spot. Second, moonlight can get in the way. A bright Moon will outshine all but the brightest streaks, so it's best to observe when the Moon is low or absent.
The next meteor shower to mark on your calendar is the Southern Delta Aquariids, which peaks on the night of 29–30 July, but requires especially dark, moon-free conditions to be seen at its best. Next comes the renowned Perseids, active from 17 July to 23 August, with their peak on the night of 12-13 August. This year, however, the near-full Moon (84%) may wash out the fainter meteors during the Perseid peak, leaving only the brighter ones visible.
Meteor shower in Wincrange / © Adriano Anfuso
Nonetheless, it's a great chance to lie down on a blanket, away from the city, and enjoy a warm night under the summer sky. And who knows, you may catch a meteor or two.
What better way to witness the dynamic nature of our Solar System in action?
Adriano Anfuso is a photographer and digital creator who is passionate about capturing the awe-inspiring beauty of the cosmos and Earth's wonders. You can check out his work here.
