What is a meteor? When is your best chance to see a meteor? Get the details in this brief guide.
Origins and characteristics of meteors
Gaze up at the sky on a clear mid-December night, and you’ll likely see shooting stars, also known as meteors, entering the atmosphere. You’re observing the Geminid meteor shower, known for being bright and intensely colored (Rendell, n.d.). In 2019, approximately 20 to 30 meteors were visible per hour during the Geminids shower (Howell 2019).
Meteors, meteorites, and meteoroids
What is a meteor? Is it a collection of shooting stars, small comets, or something different? The composition of meteors can vary. There are 3 meteorite categories based on composition analysis–chondrites, composed of stony meteorites or silicate materials, iron meteorites (primarily iron-nickel alloys), and pallasites (stony-iron) (Atkinson 2015).
Figure 1 (below) distinguishes meteors from other popular interstellar objects and defines terms.
Compare all these space objects–asteroids, meteoroids, bolides, and meteorites. What properties are used to classify them?
Approximately 25 million meteors impact Earth daily, often apart from showers, averaging speeds of 30,000 mph (48,280 kph) while reaching 3,000° F (1,648° C) upon reentry due to atmospheric friction, an effect known as ablation (Redd 2017; Schombert, n.d.). It is estimated that 1 million kilograms of meteor dust settles to the ground daily (Schombert, n.d.). Meteoroids are the precursors of meteors prior to entering the atmosphere. They vary in size, from a grain of dust to 1 meter. Asteroids, their larger cousins, range from 1 meter to hundreds of kilometers (Perlerin and Hankey 2015).
Meteoroids that reach the ground are called meteorites. The Planetary Science Institute estimates that 500 meteorites reach Earth annually, but less than 10 are recovered (Atkinson 2015). Meteorites can create spectacular craters. For example, the Barringer Meteor Crater near Winslow, Arizona, measures over 1.3 kilometers in diameter (NASA editors 2001). A meteorite traveling at 20 kilometers per second, for instance, would leave an impact crater 20 times the size of its diameter (Shaping the Planets: Impact Cratering).
Meteor showers
Meteor showers occur throughout the year, primarily originating from comets and sometimes asteroid debris. This debris creates meteoroids. Once meteoroids enter the atmosphere, friction within the atmosphere increases the temperature and makes them glow. Upon entering the atmosphere, meteoroids are known as meteors. Meteors can be brilliant, streaking across the sky with noticeable tails, sometimes exploding in the atmosphere and releasing light. These are called bolides (Perlerin and Hankey 2015).
In February 2013, a bolide estimated at 59 feet in diameter exploded over Chelyabinsk, Russia, creating an air blast and sending shock waves that exploded windows (Atkinson 2015). It is estimated that a blast equivalent to the atomic bombing of Hiroshima occurs annually, often harmlessly in the upper atmosphere (Ibid).
Meteoroids within showers are created from comets and sometimes asteroids boiling or outgassing as they approach the Sun, releasing ice and debris (Schombert, n.d.). A comet’s nucleus is a combination of “icy materials and loosely consolidated ‘dirt’” and the tail is disintegrated material from the nucleus (Lyzenga 1999). Unlike planets, comets have highly elliptical orbits and give off dust and rock, or comet debris, primarily in the inner solar system–Earth’s neighborhood. (What Is a Meteor Shower?). The Earth passes through the debris, creating meteor showers (Schombert, n.d.).
Meteor showers, such as the Geminids, occur annually around the same time and vary in strength from year to year, typically peaking shortly after a comet passes near Earth (Lyzenga 1999). One interesting phenomenon is that meteors appear to radiate from a celestial point known as the radiant because meteoroids are coming from the same aspect angle and velocity (What Is a Meteor Shower?). Meteor showers are generally named for the constellation where the radiant appears (McClure and Byrd 2019) (What Is a Meteor Shower?). See Figure 5. What constellation would you predict the Geminids’ radiant is located near?
Due to the wide field of view (FOV), meteor showers are best viewed with the naked eye or cameras with a wide FOV lens.
Famous meteor showers include the Leonids, Geminids, Orionids, Draconids, and Perseids; showers such as the Quarantids and Southern/Northern Taurids are known for producing bright fireballs, or bolides (Rendtel, n.d.). This calendar of meteor showers is based on information from the International Meteor Organization (Rendtel, n.d.).
Major meteor showers
| Meteor Shower | Time Active | Description |
| Geminids | Mid-December | Usually the strongest meteor shower. |
| Ursids | Mid-late December | Slower rates per hour. |
| Quadratids | Late December to Early January | Can be strongest shower of year but has a short duration. Average hourly rate of 25 per hour. |
| Lyrids | Mid-April | Medium strength without a persistent train but can produce up to 100 per hour. |
| Perseids | Mid-July to Late August | The most popular meteor shower, which occurs on warm summer nights. Normal rates of 50 to 75 per hour. |
| Orionids | Early October to Early November | Medium strength shower that can peak in some years. |
| Southern Taurids | Mid-September to Mid-November | Although barely visible, this shower produces many fireballs. |
| Northern Taurids | Late October to Mid-December | Active later than the Southern Taurids; especially high number of fireballs when overlapping with the Southern Taurids. High fireball counts in 7-year cycles. |
For exact annual dates see the EarthSky’s Meteor Shower Guide or purchase the US Edition of the Observer’s Handbook.
Meteor showers are wonderful natural phenomena in our night sky. From major to minor showers, meteor activity can be seen year-round. A little research is required for optimum viewing conditions, but with planning, you can see these celestial fireworks from the comfort of your backyard. EarthSky provides an up-to-date resource for meteor shower dates and viewing tips.
Additional Reading: Earth and Space Sciences in All Science Courses
Extension
Create interstellar phenomena in the classroom with the activity “Modeling a Comet in the Classroom.” It models the nucleus of a comet using dry ice and a mixture of common ingredients found in comets. By creating the model, students visualize real comet activity and gain a greater understanding of the relationship between comets and meteors.
Sources
Atkinson, N. (2015). The difference between asteroids and meteorites. Universe Today. Retrieved from https://phys.org/news/2015-06-difference-asteroids-meteorites.html
Howell, E. (2019). Geminid Meteor Shower 2019: When, Where & How to See It. Space.com. Retrieved from https://www.space.com/34921-geminid-meteor-shower-guide.html
Lunar and Planetary Institute. (n.d.). Shaping the Planets: Impact Cratering. Retrieved from https://www.lpi.usra.edu/education/explore/shaping_the_planets/impact-cratering/
Lyzenga, G. (1999). What Causes a Meteor Shower? Scientific American.
MacRobert, A. (2006). How well defined is a meteor-shower radiant? Sky & Telescope. Retrieved from https://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/how-well-defined-is-a-meteor-shower-radiant/
McClure, B., Byrd, D. (2020). EarthSky’s 2020 meteor shower guide. EarthSky. Retrieved from https://earthsky.org/astronomy-essentials/earthskys-meteor-shower-guide
NASA editors. (2001). Barringer Meteor Crater, Arizona. NASA Earth Observatory. Retrieved from https://earthobservatory.nasa.gov/images/1167/barringer-meteor-crater-arizona
Perlerin, V., Hankey, M. (2015). Meteor Terminology Poster. American Meteor Society. Retrieved from https://www.amsmeteors.org/resources/posters/
Redd, N., T., Howell, E. (2017). Meteor Showers and Shooting Stars: Formation, Facts and Discovery. Retrieved from https://www.space.com/15353-meteor-showers-facts-shooting-stars-skywatching-sdcmp.html
Rendtel, R. (n.d.). Meteor Shower Calendar. International Meteor Organization (IMO). Retrieved from https://www.imo.net/resources/calendar/
Schombert, J. (n.d.). Meteors, Asteroid and Comets Lecture, University of Oregon. Retrieved from http://abyss.uoregon.edu/~js/ast121/lectures/lec18.html
What Is a Meteor Shower? NASA. Retrieved from https://spaceplace.nasa.gov/meteor-shower/en/
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