Fireball
Fireballs are exceptionally bright meteors that appear in Earth's atmosphere, outshining Venus, and are considered a spectacular natural phenomenon. These celestial events occur when meteors, often larger than a meter across, enter the atmosphere at incredibly high speeds, generating intense heat and light due to friction with the air. While thousands of meteors enter the atmosphere daily, only a small number are classified as fireballs, with visibility affected by factors such as time of day and location. Fireballs are categorized based on their composition, with types including chondritic meteoroids from asteroids and cometary meteoroids from comets. Notably, the Perseid and Leonid meteor showers, occurring at specific times of the year, increase the chances of witnessing these bright displays. Some fireballs may explode, creating bolides that produce sonic booms and can cause damage on the ground, as seen in the 2013 Chelyabinsk event. NASA monitors near-Earth objects to track potential threats, although smaller meteors that create fireballs can be challenging to detect. Overall, fireballs present a fascinating intersection of astronomy and atmospheric science, captivating many who observe them.
Fireball
FIELDS OF STUDY: Astronomy; Observational Astronomy
ABSTRACT: A fireball is one of a small number of meteors that appear brighter in the sky than the planet Venus and may have a visible trail as they approach Earth. Fireballs are significant because they may impact on Earth or explode in the atmosphere and cause a sonic boom.
Meteors and Fireballs
Meteors are small pieces of asteroids. Every day, thousands of meteors enter Earth’s thermosphere. The thermosphere is between 80 and 120 kilometers (50 to 75 miles) above Earth. About one in every thousand meteors is a fireball. Fireballs are generally defined as meteors that appear brighter than Venus when viewed from Earth. Venus has an apparent magnitude, or degree of brightness, of between −4.9 (brightest) and −3.8 (least bright). Fireballs are also commonly called "shooting stars." They may have a visible tail of light or smoke.
The meteors that cause fireballs can be larger than one meter, or slightly more than three feet, across. As they enter the atmosphere at speeds between 11 and 72 kilometers per second (25,000 to 160,000 miles per hour), their speed puts pressure on the air. This causes the meteor to heat up to 2000 kelvins (1727 degrees Celsius or 3140 degrees Fahrenheit).
Fireballs are grouped into different classes. The classes are based on what the fireball is made of. The first two types of fireballs are chondritic meteoroids. These meteoroids are stony and come from smaller asteroids. They are created by collisions. Type 1 fireballs are ordinary chondrites. Type 2 fireballs are carbonaceous chondrites. They are rich in carbon.
The other two types of fireballs are made by cometary meteoroids. Cometary meteoroids come from comets. Type 3a fireballs come from high-density comets. Type 3b fireballs come from low-density comets.
Seeing a Fireball
Thousands of meteors with potential to be fireballs enter Earth’s atmosphere daily, but only a few are actually seen. There are different reasons for this. Meteors may fall over oceans or other areas of the planet where few people live; they may fall during daytime hours and thus be obscured by sunlight; or they may fall late at night, when most people are asleep. Experts estimate that only two to twelve fireballs per day have the potential to actually be seen by people. However, several times a year Earth passes through a meteor stream. A meteor stream is a cloud of debris left behind by a comet. When Earth passes through it, the stream creates a shower of meteors that appear to come from the same spot in the sky. The showers are named after the constellation in which that spot appears to occur. These meteor showers increase the likelihood of seeing a fireball. The Perseid meteor shower in mid-August is among the best-known showers.
The Leonid meteor shower in mid-November is also well known. The first recorded sighting of the shower was in China in 902 CE. Every thirty-three years, a peak Leonid shower phase occurs. Peak phases offer better chances of seeing a fireball. A peak Leonid shower phase took place between 1998 and 2002.
Meteorites and Bolides
While some fireballs fall all the way through Earth’s atmosphere to the surface, most are not large enough and burn up before they reach the ground. Some are large enough to reach Earth’s surface in fragments that are called meteorites. Experts say that these pieces of debris cool as they complete their fall to Earth and are not generally hot once they land. Usually only fireballs with a magnitude of −8 or brighter will reach Earth’s surface as meteorites.
Some fireballs explode as they enter the atmosphere. They create a brilliant flash of light followed some time later by a sonic boom, a loud explosion-like noise that objects make when they travel faster than the speed of sound. These loud, explosive fireballs are called bolides. They may cause damage on the ground. The meteor that shattered windows and rattled buildings in Cheylabinsk, Russia, in February 2013, injuring more than one thousand people and causing more than $30 million in damages, exhibited the fiery appearance and sonic boom characteristic of a bolide.
The National Aeronautics and Space Administration (NASA) operates a near-Earth object (NEO) detection system and monitors space objects such as asteroids that could threaten Earth. However, some objects, such as the meteors that become fireballs and bolides, are small and therefore difficult to observe and track.
Principal Terms
- bolide: a fireball that explodes in Earth’s atmosphere and creates a sonic boom.
- meteor: a piece of rock or metal that enters Earth’s atmosphere and becomes visible as a burning, glowing streak in the sky. The streak of light is also called a meteor.
Bibliography
"Fireball." Cosmos: The SAO Encyclopedia of Astronomy. Swinburne U of Technology, n.d. Web. 9 Mar. 2015.
"Fireball and Bolide Reports." Near Earth Object Program. NASA, 9 Mar. 2015. Web. 9 Mar. 2015.
"Fireball FAQs." American Meteor Society. Amer. Meteor Soc., 2013–15. Web. 9 Mar. 2015.
"Fireball Observations." International Meteor Organization. Intl. Meteor Org., 1997–2013. Web. 9 Mar. 2015.
Kuzmin, Andrey. "Meteorite Explodes over Russia, More Than 1,000 Injured." Reuters. Thomson, 15 Feb. 2013. Web. 9 Mar. 2015.
"Meteors & Meteorites." National Aeronautics and Space Administration. NASA Science, 6 May 2021, solarsystem.nasa.gov/asteroids-comets-and-meteors/meteors-and-meteorites/overview/. Accessed 16 June 2022.
NASA’s All Sky Fireball Network. NASA, 8 Mar. 2015. Web. 9 Mar. 2015.
"Near Earth Asteroids (NEAs): A Chronology of Milestones, 1800–2200." International Astronomical Union. IAU, 7 Oct. 2013. Web. 9 Mar. 2015.