Meteor showers occur when the Earth collides with a collection of particles also orbiting the Sun. It is usually believed that these particles of ice and dust are the remnants of comets that once passed through the inner solar system. When these meteoroids enter the Earth's atmosphere, friction with the air causes them to heat up and glow. This is what causes meteors, the brief streaks of light that you see in the sky. Most meteoroids burn up completely in the atmosphere but occasionally one survives to actually hit the Earth. This object is then termed a meteorite. Meteorites are subdivided into two main categories: stones (stony meteorites) and irons (iron-nickel meteorites).
Not all meteorites are pieces of comets. A number of meteorites have been found in the Antarctic which have been traced back to our neighbouring planet Mars! Some scientists even believe that a few of these objects contain microfossils of ancient Martian bacterial life. Larger meteorites may be pieces of asteroids. Many people believe that the great extinction at the end of the Cretaceous period was caused by a large asteroid hitting the Earth. The resulting dust cloud then cooled the Earth and caused many species to die out, including the dinosaurs.
Meteors can be seen on any clear night although they are usually more prevalent after midnight. If you are lucky, you might glimpse a sporadic bolide or fireball. However, your best chance for seeing meteors is during a meteor shower. These are not confined to a single night but are spread out over a period of days or weeks with a peak at a given time. An optical illusion makes it appear that all the meteors in a shower are emerging from a single point called the radiant. However, the meteors are actually travelling in parallel. As an analogy, look at a set of straight railroad tracks. The tracks are parallel but the farther into the distance you look at them, the closer they appear to get until they converge. In the same way, perspective makes it appear as if meteors in a shower are originating from a common point.
Here is a list of the major meteor showers. A three-day span is given for the peak activity of the showers due to the unpredictable nature of this phenomenon. The Zenithal Hourly Rate is the theoretical maximum of meteors an observer would see in perfect skies with the radiant overhead. A variable ZHR is indicated with the letter V.
|Quadrantids||00010 QUA||late December to mid‑January||2‑4 January||120||average||bright||probably asteroid 2003 EH1 which in turn may be (a fragment of) comet C/1490 Y1|
|Lyrids||00006 LYR||mid- to late April||21‑23 April||18||average||bright||C/1861 G1 Thatcher|
|π Puppids||00137 PPU||mid- to late April||22‑24 April||V||slow||bright||26P/Grigg‑Skjellerup|
|η Aquariids||00031 ETA||mid-April to late May||5‑7 May||50||fast||bright||1P/Halley|
|Arietids||00171 ARI||mid-May to late June||6‑8 June||30||average||average|
|June Boötids||00170 JBO||mid-June to early July||26‑28 June||V||slow||bright||7P/Pons‑Winnecke|
|Southern δ Aquariids||00005 SDA||mid‑July to mid‑August||29‑31 July||25||average||faint|
|Perseids||00007 PER||mid‑July to late August||11‑13 August||150||fast||bright||109P/Swift‑Tuttle|
|Draconids||00009 DRA||early October||7‑9 October||V||slow||average||21P/Giacobini‑Zinner|
|Orionids||00008 ORI||early October to early November||20‑22 October||15||fast||bright||1P/Halley|
|Leonids||00013 LEO||early to late November||16‑18 November||15||very fast||bright||55P/Tempel‑Tuttle|
|α Monocerotids||00246 AMO||mid- to late November||20‑22 November||V||fast||bright|
|Phoenicids||00254 PHO||late November to early December||5‑7 December||V||slow||average||289P/Blanpain (formerly D/1819 W1 Blanpain which was rediscovered as asteroid 2003 WY25 and then later found to have a coma)|
|Puppid‑Velids||00301 PUP||early to mid‑December||6‑8 December||10||average||average|
|Geminids||00004 GEM||early to mid‑December||13‑15 December||120||average||average||3200 Phaethon|
|Ursids||00015 URS||mid- to late December||21‑23 December||10||average||faint||8P/Tuttle|
Meteor shower information is provided by the International Meteor Organization.