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The life of a meteor starts with a comet. These are objects which orbit the Sun in long, thin orbits and each time a comet comes near the Sun, it loses part of its mass. This begins to orbit in an orbit similar to that of the comet. Occasionally the Earth enters one of these streams of particles and some of the particles enter the atmosphere. As they are moving at high velocity, friction occurs, slowing the particles but making them shine brightly. An observer on the ground will see something bright (around the brightness of a star) moving quickly across the sky, hence the expression - a shooting star, or meteor.
As a meteor shower occurs when the Earth enters a stream of particles, most repeat on an annual basis. A meteor shower is characterised by all members coming from the same point in the sky (known as the radiant). The shower is named after the constellation in which the radiant lies.
Some showers are given below
|Quadrantids||January 1-6||100||Short Active Maximum|
|Lyrids||April 19-25||10||Higher activity not unknown|
|Delta Aquarids||July-August||10||One of several southern showers|
|Perseids||July 25 to August 20||80||Higher activity in early nineties|
|Orionids||October 16-26||25||Morning Shower|
|Leondis||November 15-20||?||Activity rising|
|Geminids||December 7-15||100||Visible many hours each night|
The term ZHR stands for zenithal hourly rate, a guide to how active a shower is. The ZHR is the number of meteors an observer would see in an hour with the radiant directly overhead and in perfect conditions.
The Quadrantid shower is named after the former constellation of Quadrans Muralis. The radiant is now in the constellation of Bootes.
The Leonid shower is unusual in that activity varies greatly from year to year. At some times, e.g. mid eighties, activity is in the 5-10 per hour range. However, at other times e.g. 1799, 1833, 1866, 1966 activity has been many thousands per hour. For several years once every 33 years (period of parent comet Temple-Tuttle) there is a chance of such high activity. It is too early to say whether such activity will occur in 1999-2000 but activity has certainly been rising through the nineties.
Highest Activity around April 21/22
Highest Activity perhaps 10-20 per hour
Higher activity occasionally observed
Radiant in Lyra - between Vega and the Hercules Border
Highest Activity around August 12
Highest Activiy around 80-100 per hour
Enhanced Activity in Early nineties
Radiant in Northern Perseus, spends some time in Casseopiea and Camelopardalis
Active July and August
Each shower around 5 per hour .... but together they add up
Put simply, the instructions for observing meteors visually are short !
1) Take a dark, clear night
2) Find a good observing site
3) Look at the sky and see meteors
Clearly, it is possible to expand on these points. A dark, clear night is essential if many meteors are to be seen. The standard limiting magnitude is 6.5 but if the sky is slightly hazy, e.g. limiting magnitude 5.0, only about a quarter of the meteors can be seen. Similarly, if the radiant is low down fewer meteors will be seen than if the radiant is riding high in the sky. It helps to bring a deck-chair or similar so that there is no strain of having your neck at an awkward angle. It is also worth taking various supplies e.g. refreshments, extra clothes etc.
Choice of observing site depends very much on individual circumstances. In some rural or semi-rural areas a garden may be appropriate. Travel may be required; if this is the case, it is best to plan this in advance. It is not easy to arrive in an area and know what will be a good site. In addition, some thought may be necessary concerning landowners etc.
Obviously, simply looking at meteors and enjoying them is fine. However, with a very little extra effort, a report of serious scientific value can be made. The British Astronomical Association Meteor Section produces forms for this purpose. Please contact me if interested.
Observing meteors photographically is something of a hit or miss business. It is not feasable to begin an attempt to photograph a meteor once it has become visible. Instead, a photograph must be taken of an area of sky with the hope that a meteor will cross that area.
The same comments about observing site, weather etc apply to photographic observation as to visual observation. Almost any camera is suitable; the main requirement is that the shutter must remain open for an indefinite period of time (with the aid of a cable release where necessary). Film speeds vary, as do exposures; one possibility is 400 ASA film and 10 minute exposures. However, if 3200 ASA film is used exposures should be cut to around one minute. Obviously colour film gives 'nicer' pictures; however, black and white film is better for making measurements from.
The BAA Meteor Section promotes and analyses meteor observing world-wide. Papers describing the work of the section can be found in recent issues of the BAA Journal.
Meteor Page of The Astronomer Magazine.
Picture of a Perseid Meteor (S Kohle and B Koch.
Leonid Storm in 1998 Prof. I. Williams, QMW
Link to British Astronomical Association
Link to North West Group
Link to Kronk and Young's Meteor Page
Link to Abstracts of papers on meteors by Ken Fox
Link to Bob Riddle's Meteor Pages
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