Meteor shower definition
Most meteors can occur at any time and in any direction. They belong to what is called the sporadic meteors. Their origin is mostly related to asteroids. They constitute the bulk of meteors falling into the Earth's atmosphere.
However, there is a second population of meteors associated with dust released along the orbit of a comet. When a comet approaches the Sun, it warms up and releases dust grains along its orbit. If Earth is crossing the orbit of this comet, it passes every year at the same time into a cloud of dust particles which produces a meteor shower.
Due to a geometrical effect, all meteors belonging to a meteor shower seem to come from one point in the sky called the radiant. Each meteor shower is named after the constellation this point belongs to. For example, the radiant of the Perseids is located in the Perseus constellation.
Here we discuss the current three most active meteor showers:
Perseids (in August)
The Perseids is the most well known meteor shower, because it is visible during summer in the northern hemisphere, and it has a broad maximum (you can also observe a lot of Perseids the nights before the peak on August 12). However the ZHR profile (the number of meteors an observer would see at the highest region of the sky under ideal circumstances) is skewed with a steeper decrease after the maximum period.
The meteors are called the Perseids because the point from which they appear to hail (called the radiant) lies in the constellation Perseus. The best moment to observe these meteors in Belgium is in the morning, when the radiant is located high in the sky.
The Perseids have been observed for at least 2000 years now. The first information on them came from the Far East. In 1864–1866, after the perihelion passage of comet Swift-Tuttle in 1862, the Italian astronomer Giovanni Virginio Schiaparelli discovered the link between meteor showers and comets.
- Period: July 17–August 24
- Maximum: August 12
- Max ZHR: 100
- Population index: 2,2
- Velocity: 60 km/s
- Parent body: 109P/Swift-Tuttle
Geminids (in December)
The Geminids are a prolific meteor shower caused by the object 3200 Phaethon, which is thought to be an asteroid of the same type as 2 Pallas. This would make the Geminids, together with the Quadrantids, the only major meteor showers not originating from a comet.
The meteors from this shower are much slower (35 km/s) than most other meteor showers, can be seen in December and usually peak around December 7-17, with the date of highest intensity being the morning of December 13.
The meteors in this shower appear to come from the radiant in the constellation Gemini (hence the shower's name). However, they can appear almost anywhere in the night sky, and often appear yellowish in hue.
- Period: December 7–17
- Maximum: December 13
- Max ZHR: 120
- Population index: 2,6
- Velocity: 35 km/s
- Parent body: 3200 Phaethon
Quadrantids (in January)
On January 3 and 4, you can observe the Quadrantid meteor shower. The zenithal hourly rate (ZHR) of this shower can be as high as that of two other reliably rich meteor showers, the Perseids in August and the Geminids in December. Yet Quadrantid meteors are not seen as often as meteors in these other two showers, because the peak intensity is exceedingly sharp, lasting only a few hours.
In Belgium (~51° N) its radiant (the point from which they appear to hail) in the constellation Boötes is circumpolar (i.e. never goes below the horizon).
The name comes from Quadrans Muralis, a former constellation that is now part of Boötes.
- In early January 1825, Antonio Brucalassi in Italy reported that “the atmosphere was traversed by a multitude of the luminous bodies known by the name of falling stars.”
- In 1839, Adolphe Quetelet, the first director of the Brussels Observatory (currently the Royal Observatory of Belgium), and Edward C. Herrick in Connecticut independently made the suggestion that the Quadrantids are an annual shower.
The meteoroid stream of the Quadrantids is recently linked to the comet 96P/Machholz 1 and the minor planet 2003 EH1 (likely a comet that has gone dormant in the past few hundred years). Scientists believe that the minor planet is responsible for the core activity (lasting ~0,5 days), while dust from the comet causes the broader, longer-lived (~4 days) background activity.
- Period: December 28 – January 12
- Maximum: January 3
- Max ZHR: 120
- Population index: 2,1
- Velocity: 41 km/s
- Parent bodies: 96P/Machholz 1 & 2003 EH1