What's The Difference Between A Meteor, Comet And Asteroid?

At approximately 12am tonight, the 2017 Perseid Meteor Shower is set to wow the world. Many eyewitnesses will use the words "meteor", "meteorite", "comet" and "asteroid" interchangeably to describe the celestial event they're seeing.

In reality, these are all completely different types of space rock. If you want to avoid a social faux pas tonight (or want to be the smarty-pants who corrects fellow stargazers), here's what sets each type apart.

How To Watch Tonight's Perseid Meteor Shower In Australia

The Perseid Meteor Shower is set to peak on the night of August 12 and early morning hours of August 13 AEST. It's a bit of a difficult one to spot in Australia as the radiant doesn't rise very far above the horizon in the Southern hemisphere. With that caveat out of the way, here are some tips to increase the odds of catching a meteor or two this week.

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So what are we looking at tonight: Meteors, comets or asteroids? And what's the difference between a meteor and a meteorite? We'll let the experts over at NASA clear up any confusion you might be feeling.

The following definitions come from the official NASA Dictionary of Technical Terms for Aerospace Use. Here they are, in alphabetical order:

Asteroid: One of the many small celestial bodies revolving around the sun, most of the orbits being between those of Mars and Jupiter. All asteroids with determined orbits are numbered for identification in the order of their discovery.

Comet: A luminous member of the solar system composed of a head, or coma, and often with a spectacular gaseous trail extending a great distance from the head. The orbits of comets are highly elliptical.

Meteor: In particular, the light phenomenon which results from the entry into the earth's atmosphere of a solid particle from space; more generally, any physical object or phenomenon associated with such an event.

Meteorite: Any meteoroid which has reached the surface of the earth without being completely vaporized.

Hmm, I never realised astronomers were so laconic. The definitions on Wikipedia provide some additional information on how each celestial body differs:

Comet: A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles.

Asteroid: Asteroids (from Greek ἀστήρ 'star' and εἶδος 'like, in form') are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones. These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet and was not observed to have the characteristics of an active comet, but as small objects in the outer Solar System were discovered, their volatile-based surfaces were found to more closely resemble comets, and so were often distinguished from traditional asteroids

Meteor: A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are called a meteor shower. The root word meteor comes from the Greek meteo¯ros, meaning "high in the air".

And here are some other phrases from NASA's dictionary that it wouldn't hurt to know:

Celestial body: Any aggregation of matter in space constituting a unit for astronomical study, as the sun, moon, a planet, comet, star, nebula, etc.

Coma: 1. The gaseous envelope that surrounds the nucleus of a comet. 2. In an optical system, a result of spherical aberration in which a point source of light, not on the axis, has a blurred, comet-shaped image.

Meteoroid: A solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule.

Meteoritics: The study of meteorites and meteoric and meteoritic phenomena.

Meteor path: The projection of the trajectory of a meteor in the celestial sphere as seen by the observer.

Meteor shower: A number of meteors with approximately parallel trajectories.

Meteor stream: A group of meteoric bodies with nearly identical orbits.

Meteor trail / Meteor train: Anything, such as light or ionization, left along the trajectory of the meteor after the head of the meteor has passed.

Meteor wake: Meteor train phenomena of very short duration, in general much less than a second.

Micrometeorite: A very small meteorite or meteoritic particle with a diameter in general less than a millimeter.

And finally, here are some celestial factoids to casually drop while everyone's starring skyward:

  • "The term minor planet is preferred by many astronomers but asteroid continues to be used in astronomical literature."
  • "The brightest examples of shooting stars are called 'bolides'."
  • "Meteorites that are recovered after being observed as they transit the atmosphere or impact the Earth are called 'meteorite falls'. All others are known as meteorite 'finds'."
  • "Meteorites are divided into three broad categories: 'stony meteorites' which mainly composed of silicate minerals, 'iron meteorites' which are largely composed of metallic iron-nickel and 'stony-iron meteorites' which contain large amounts of both metallic and rocky material. Around 94 per cent of all meteorites are the stony type."
  • Meteorites are easy to recover in the desert regions of Australia. This is because the land presents a flat, featureless, plain covered by limestone."
  • "The cult in the Temple of Artemis at Ephesus, one of the Seven Wonders of the Ancient World, is thought to have originated with the observation of a meteorite fall. A sacred stone inside the temple's shrine may have been this same meteorite."
  • "Do you know that when you look at a planet and you see that light, that planet's not even there: that's just a light, that's just your neighbour shining a flashlight right into your yard looking for 'coons. And he says "what are you doing in my backyard with that flashlight?" And I told him: "I'm shining, I'm shining in the window so I can teach your son about the universe." He said, "get out of my yard and why are you communicating to my son? Why are you in all black, behind my bushes shining a light into my house?" and I said "I'm teaching your son about the universe! I'm shining a light, shining a light right in there and exploring his room as he's looking out and exploring the universe!" I turn the light off and I see your son go to bed and I turn the light back on and I do swirls on his wall like a comet's tail. I do this every night with your son."

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General knowledge is important. While it might not come up in everyday life, it's an effective intelligence barometer that can colour people's perception of you and leave your reputation permanently tarnished. This got us to thinking -- how much does the average human actually know about the solar system? Take our quiz to find out!

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