Glossary

AU

Astronomical Unit. The mean distance between the Earth and Sun, equal to about 150 million kilometers (or about 93 million miles).

asteroid

an icy dirtball that orbits the Sun typically on a almost-circular orbit. Asteroids used to be thought of as solid chunks of rock but in the past few decades it was realized that most of them are probably 'rubble piles' of rock held together by their weak gravitational attraction with some ice incorporated into the mixture. Asteroids are generally more rocky than icy.

bolide

a very bright meteor also known as a fireball. They are considered bright if they are brighter than the brightest planet, Venus. Typically caused by a chunk of rock entering the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and quickly burning up at an altitude of about 100 km (60 miles).

C-type

asteroids are classified into different types by their spectra - the colors of their surface. C-type asteroids have a grayish color. The color is thought to indicate that their surfaces are composed of carbonaceous material. Kind of like soot from a fire.

CCD

Charge Coupled Device. This is the light sensitive 'film' in modern digital cameras - from your little point-and-shoot, to the fine digital SLR cameras, to the cameras for the ATLAS system. Basically, light is captured on little electronic 'pixels' that can be directly read out and displayed on a computer screen. For more detailed information see Wikipedia's CCD page.

comet

a dirty iceball that orbits the Sun. Comets used to be thought of as solid chunks of ice but in the past few decades it was realized that most of them are probably 'rocky snowballs' held together by their weak gravitational attraction. Comets are generally more icy than rocky.

fireball

a very bright meteor also known as a bolide. They are considered bright if they are brighter than the brightest planet, Venus. Typically caused by a chunk of rock entering the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and quickly burning up at an altitude of about 100 km (60 miles) due to friction with the Earth's atmosphere.

M-type

asteroids are classified into different types by their spectra - the colors of their surface. M-type asteroids have colors that indicate that much of their surface is covered by metals like iron and nickel.

meteor

often known by the term 'falling star' like this website, a meteor is the quick and bright flash of light in the night sky produced when a small piece of rock enters the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and burns up at an altitude of about 100 km (60 miles) due to friction with the Earth's atmosphere. A bright meteor might be caused by a pea-size piece of rock. Most the ones you see are the size of grains of sand. Most meteors burn up entirely in the atmosphere creating a fine dust that settles down to the ground.

meteorite

if a large meteor (a bolide) fails to burn up in its passage through the atmosphere some part of it might strike the Earth. The remnant that survives on the Earth's surface is called a meteorite.

meteoroid

the chunk of rock in space before it strikes the Earth's atmosphere. Meteoroids and asteroids that will strike the Earth's atmosphere.

NEO

Near Earth Object. An asteroid or comet that approaches to within 1.3 astronomical units (AU) of the Sun.

orbit

the path of an object around another object. For instance, the moon 'orbits' the Earth and, in turn, the Earth 'orbits' the Sun. Orbits are typically elliptical i.e. egg shaped or oval.

PHO

Potentially Hazardous Object - An asteroid or comet that is larger than 150 meters in diameter (about 500 feet) and that can approach to within 0.05 astronomical units (AU) of the Earth's orbit. This does not mean that it approaches the Earth to within this distance - just the Earth's orbit. These objects are considered hazardous because they are large enough to cause widespread damage upon impact and because even though they may not approach the Earth closely now, their orbits can change over the course of about a hundred years to make them Earth-impacting objects. They therefore warrant attention.

S-type

asteroids are classified into different types by their spectra - the colors of their surface. S-type asteroids have a reddish color. The color is thought to indicate that their surfaces are composed of silicate material. Kind of like beach sand.