Meteors are commonly known as ‘shooting stars’ or ‘falling stars’, and are one of the most exciting things to see in the night sky, particularly for amateur stargazers. The night sky itself is a wondrous sight, but to see a fleeting streak of movement in the darkness, knowing that part of the heavens has fallen to Earth, is particularly special.
In its simplest definition, a meteor is the visible trail of light that is seen when a meteoroid enters the Earth’s atmosphere at thousands of miles an hour and is heated to extreme temperatures, breaking up and often burning up completely, leaving a trail of superheated gases and dust behind it. These trails of light typically only last for a second or so, although larger meteors may leave a longer lasting trail.
A meteor or shooting star can be produced by a meteoroid as small as a speck of dust or grain of sand, or as big as tens of meters in diameter. Typically, a shooting star that is bright enough to be seen fairly clearly in the night sky is produced from meteoroids around the size of an average pebble, a few centimetres across.
It is well worth at this point explaining the meanings of three words that are sometimes confused or misused. A ‘meteor’ is the term given to the light trail seen as a piece of rock burns up in the atmosphere. A ‘meteoroid’ is the piece of rock itself while it is in space, and a ‘meteorite’ is the term given to a meteoroid, or the remainder of it, that survives the heat of its entry into the atmosphere, and makes it to the surface of the Earth.
It is also worth noting, that meteors occur both day and night as the Earth spins on its journey through space. It is relatively rare for a large meteor to be bright enough to be seen during daylight hours, but it does happen.
The meteoroids themselves are mainly rocky, containing silicate minerals. A smaller proportion of them are stony-metal consisting of a mixture of rock and metal such as iron. They are in effect the left overs in space that have so far not become a part of a larger body through coalescence or collision.
The first ‘type’ of meteor is simply termed as a ‘meteor’, under the definition given in the previous paragraphs, with the addition that it is a meteor that does not reach a magnitude of greater than -4 (is not brighter than any of the planets visible in the night sky).
The next type of meteor is termed by astronomers as either a ‘bolide’ or simply a ‘fireball’. There is no real definition for the term bolide, and it is generally synonymous with the term fireball, a meteor that has a magnitude of greater than -4, which is brighter than any of the planets visible in the night sky.
The third type of meteor is termed as a ‘superbolide’ and is a meteor that reaches a magnitude or brightness of greater than -17.
There is another type of meteor, one that in effect bounces off the Earth’s atmosphere and returns to space, and this is termed as an ‘earth grazing fireball’. A good example of an earth grazing fireball is ‘the great daylight’ of 1972, when a large fireball was witnessed for some half a minute or so over the skies of the north-western USA and parts of Canada.
Meteors also sometimes come in ‘showers’. These meteor showers are generally the result of the Earth, as it travels through space, passing through a relatively dense concentration of dust and rocks in the form of the debris trail left behind in space by a comet.
Notable meteor showers are the Leonids, occurring in mid November each year, and the Perseids, which occur in mid August. Meteor showers have been known over the years to provide spectacular displays of many hundreds and even thousands of individual meteors per hour.
