Meteor Showers: Perseids, Leonids, Geminids...

Where do these luminous trails come from?

Despite their poetic name, shooting stars are not stars at all. They are particles of dust smaller than a millimeter (no larger than a grain of sand) that originate from the disintegration of a comet or asteroid. These grains of matter, called meteoroids, enter Earth's atmosphere at speeds between 11 km/s and 72 km/s. Friction with air molecules compresses and heats these particles until they completely vaporize, producing a streak of light visible from the ground: this is a meteor.

When Earth passes through the dusty trail left by a comet in its orbit, hundreds or even thousands of meteoroids enter the atmosphere simultaneously. This predictable and recurring spectacle occurs every year on the same dates, forming a meteor shower. The most famous include the Perseids, Leonids, and Geminids.

Why do major meteor showers repeat every year?

The origin of this dust is almost always linked to comets. As comets approach the Sun, their ice sublimates, releasing a stream of rocky and dusty particles that form their coma and long luminous tail. Along their orbit, comets leave behind a ribbon of debris. Every year, when Earth passes through this "river of dust" at the same time, the phenomenon repeats, giving rise to meteor showers.

Where do shooting stars come from?

Each shower is distinguished by its radiant: the point in the sky from which the trails appear to diverge, due to a perspective effect. The name of the shower is derived from the constellation where this radiant is located. This apparent point of convergence gives each shower its name: the radiant of the Perseids is in the constellation Perseus, that of the Leonids in Leo, and that of the Geminids in Gemini.

The height of the radiant above the horizon directly influences the number of observable meteors. The higher the radiant is in the sky, the more numerous and longer the meteors are. This is why a shower's activity reaches its maximum after midnight, when the radiant is at its highest. The activity rate is expressed in ZHR (Zenithal Hourly Rate), a theoretical value standardized for a perfect sky.

The Perseids: The Summer Shower

The Perseids are a meteor shower, yellow to orange in color, sometimes green, active every year from July 17 to August 24. They peak around August 11-12, with a ZHR that can exceed 100 meteors per hour under a dark sky. Their entry speed into the atmosphere is about 59 km/s, which often generates persistent trails and particularly spectacular colored fireballs.

The parent comet of the Perseids is comet 109P/Swift-Tuttle, discovered in 1862 by Lewis Swift and Horace Parnell Tuttle. Its nucleus is about 26 km in diameter, making it one of the largest known comets to regularly approach Earth. It completes a full orbit around the Sun in about 130 years; its next perihelion passage will be on July 12, 2126. With each revolution, the comet ejects new particles that settle on the same orbit and overlap with debris from previous passes, enriching the stream over millennia. Gravitational perturbations from Jupiter and Saturn spread these particles along a portion of the orbit, forming distinct filaments.

The Leonids: The Storm Shower

The Leonids are active every year from November 6 to 30, with a peak around November 17-18. Their particularity lies in their exceptional speed: they enter the atmosphere at about 71 km/s, the highest speed of all major meteor showers. These are very bright meteors, white-bluish or pure white, which leave persistent trails lasting several seconds.

The comet responsible for the Leonids is 55P/Tempel-Tuttle, a periodic comet whose 33-year orbit replenishes the meteor stream responsible for this meteor shower every year. First identified in 1865 by Wilhelm Tempel and independently in 1866 by Horace Parnell Tuttle, this comet offers an exceptional show every 33 years: when Earth crosses areas of the stream recently replenished by its passage near the Sun, the Leonids turn into true meteor storms.

These storms can reach several thousand, or even tens of thousands of meteors per hour (estimated at 150,000 meteors/hour in 1966). The last perihelion occurred in 1998, resulting in spectacular storms between 1999 and 2002. The next passages are expected around 2031 (with visible effects around 2034, as the debris disperses) and 2064 (with a peak around 2065).

The Geminids: The Shower from Asteroid Phaethon

The Geminids stand out from other meteor showers due to their unique origin: they do not come from a comet, but from an asteroid, (3200) Phaethon, about 5 km in diameter. This celestial body has a rare feature for an asteroid: it develops a dust trail similar to that of a comet when it approaches the Sun. Phaethon's perihelion passage occurs every 1.43 years (about 524 days).

Every year, Earth passes through the same point in its orbit around December 13, and this is precisely where the trail of debris left by Phaethon is located. The Geminids are active from December 4 to 20, with a peak around December 13-14. With a ZHR that can reach 120 to 150 meteors per hour, they are already active in the early evening, when the radiant rises around 8 PM in Gemini. The meteors enter the atmosphere at about 35 km/s, a moderate speed that gives them a green, yellow, or sometimes white color.

Table of Major Meteor Showers

N.B.: ZHR (Zenithal Hourly Rate) is the theoretical number of meteors visible per hour under a perfectly dark sky, with the radiant at the zenith. The values indicated are averages; some years, higher peaks may occur. The colors mentioned are those generally observed, but may vary depending on the composition of the meteors and observation conditions.

FAQ – Shooting Stars