Meteor Showers

Never tell me that not one star of all
That slip from heaven at night and softly fall
Has been picked up with stones to build a wall.
— Robert Frost, "A Star in a Stone Boat", 1923

Meteoroids, Meteors and Meteorites

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.

Major Meteor Showers

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 letters Var.

Name Code Activity Peak Activity ZHR Velocity (km/s) Parent
Quadrantids 010 QUA late December to mid-January 2–4 January 80 41 probably asteroid 2003 EH1 which in turn may be (a fragment of) comet C/1490 Y1
α Centaurids 102 ACE early to mid-February 7–9 January 6 58
Lyrids 006 LYR mid- to late April 21–23 April 18 49 C/1861 G1 Thatcher
π Puppids 137 PPU mid- to late April 22–24 April Var 18 26P/Grigg-Skjellerup
η Aquariids 031 ETA mid-April to late May 5–7 May 50 66 1P/Halley
Arietids 171 ARI mid-May to late June 6–8 June 30 38 possibly 96P/Machholz
June Boötids 170 JBO late June to early July 26–28 June Var 18 7P/Pons-Winnecke
Southern δ Aquariids 005 SDA mid-July to late August 29–31 July 25 41 possibly 96P/Machholz
Perseids 007 PER mid-July to late August 11–13 August 100 48 109P/Swift-Tuttle
Aurigids 206 AUR late August to early September 29–31 August 6 66 C/1911 N1 Keiss
September ε Perseids 208 SPE early to mid-September 8–10 September 8 64
Draconids 009 DRA early October 7–9 October 5 20 21P/Giacobini-Zinner
Orionids 008 ORI early October to early November 20–22 October 20 66 1P/Halley
Southern Taurids 002 STA late September to late November 5–6 November 7 27 2P/Encke
Northern Taurids 017 NTA late October to mid-December 11–13 November 5 29 2004 TG10
Leonids 013 LEO November 16–18 November 10 71 55P/Tempel-Tuttle
α Monocerotids 246 AMO mid- to late November 20–22 November Var 65
Phoenicids 254 PHO late November to early December 1–3 December Var 15 289P/Blanpain (formerly D/1819 W1 Blanpain which was rediscovered as asteroid 2003 WY25 and then later found to have a coma)
Puppid-Velids 301 PUP early to mid-December 6–8 December 10 44 26P/Grigg-Skjellerup
σ Hydrids 016 HYD early to mid-December 8–10 December 7 58
Geminids 004 GEM early to mid-December 13–15 December 150 35 3200 Phaethon
Ursids 015 URS mid- to late December 21–23 December 10 33 8P/Tuttle