Introduction to Meteor Observing

By Pierre Martin

Of all celestial events, few can be more breathtaking than a good meteor shower or a bright, colourful fireball racing against the starry backdrop. Meteor observing is one of the few astronomical activities that requires very little optical equipment. In fact, the best way to see them is to use nothing more than your naked eyes and some patience!



Typical swift moving meteors usually last only a fraction of a second.

On any clear moonless nights, you can expect to see at least a few meteors per hour moving from random directions. These unpredictable stray meteors are called sporadics. Meteors are often referred to as a "shooting" or "falling" stars. In reality, stars do not shoot, nor do they fall. Meteors are defined by the brilliant streak of light created by meteoroids from outer space. A meteoroid is a particle of rock or dust in space. Once it enters the upper earth atmosphere at speeds of up to 70 kilometres per second, tremendous air friction will heat it up rapidly. As the meteor slows down in its descent into the atmosphere, it interacts with surrounding gas and ionizes. Usually, not more than a fraction of a second after all this, the particle itself vaporizes completely. We see this ablation process as a brief streak of light in the night sky.

Meteorites
In some cases, when the meteoroid is large enough to survive the trip into the atmosphere, it may fall on the ground and produce a meteorite. Small meteorites are common. Several may lie hidden on the surface among other natural earth rocks. Meteorites are valuable to scientists as they provide important clues to unlock the many secrets of our own Solar System. Some rarer meteorites may be considerably large and produce a crater on the surface. One famous example is Meteor Crater in Arizona, USA that was produced only several thousands years ago from an object the size of a school bus. Scientists believe a giant meteorite may have caused the extinction of the dinosaurs 65 million years ago.

Meteor showers
Every year on the same dates, you will notice that the number of meteors visible will increase considerably. This is when we assist to a meteor shower. A meteor shower happens when the earth encounters a stream of dust particles left behind by a comet. A comet is comparable to a very large "dust" and "snow" ball. It is mostly composed of brittle material. As the comet approaches the sun, it will heat up and release some of its dust behind. With time, this dust accumulates more or less along the orbit to form a stream. There's nearly a dozen major annual meteor showers and several more minor ones, the result of our planet plowing through several dust streams. The two most reliable and well known meteor showers are the Perseids on August 12 and the Geminids on December 14. For a list of the annual meteor showers, please take a look at our calendar within the Meteor Section links.

It's all perspective
We name meteor showers for the constellation from which they appear to radiate. Since shower meteors travel in parallel paths, we get the illusion of perspective, an effect similar to standing on railway tracks and seeing the rails converge to one point at the horizon. When you trace these meteors back following a straight line, they seem to intersect with a point in the sky called the radiant. So meteors with the radiant in the constellation Perseus are called Perseids, Geminids would radiate from Gemini and so on... Keep in mind that meteors can and will appear anywhere in the sky, even far away from their radiant.



"How many will I see tonight?"
Most annual meteor showers usually provide only a "sprinkle" of meteors. The showers described above can provide displays of up to 60 to 100 meteors per hour from dark, moonless skies away from the city. In some years, they have been known to produce even more. Some meteor showers have produced some incredible rates in the past, which is rare. For instance, the normally weak Leonids of November 17 return every 33 years to produce some enhanced activity. In 1966, the Leonids exploded in an amazing "storm" of meteors with over 140 000 visible in one hour for observers along the west coast of North America. After a long relatively quiet period of Leonids, they have finally returned in recent years to roar back to life. A "storm" of about 3000 meteors per hour has been observed over Europe and Asia in 1999, and then above North America in 2001 and 2002. To see such rare memorable displays, you must be at the right place and at the right time, otherwise you miss out.
The highest numbers of meteors on most nights usually happens after midnight. In the evening hours, meteors are slow. They must catch up with us, as the earth rotates away from most incoming material. After midnight, we find ourselves turning directly into the incoming particles. So in the early morning hours before dawn, meteors come in faster and in greater numbers overall.

Meteor observing can be a test of patience. Even a good Perseids or Geminids shower will still produce on average 1 or 2 meteors per minute. The meteors also rarely arrive right on cue. Sometimes you will watch several minutes with no meteors, then the next minute will unexpectably burst with 5 or 6. Sometimes you will see a faint streak on the corner of your eye and you will say "Did I really see something?". But meteor observing has its rewards.

"Oooh, Ahhh!!!"
Sooner or later you will see a meteor that will rival or surpass the brightest star in the sky and make the others around you exclaim in a "Wowwwww!!!!". Such bright meteors can exceed the brightness of Venus and are called fireballs. A fireball is caused by a larger chunk of rock burning up in the atmosphere. Such bright events may leave behind a vaporous looking train that may persist for several seconds or eve minutes. Trains are the result of an ionization process. Sometimes, very bright fireballs may penetrate deeper in the atmosphere and produce sonic booms, audible several seconds or minutes after. Observers reported sonic booms sometimes barely audible and sometimes as loud as a clap of thunder. More controversial is the appearance of a meteor with a sound occurring at the SAME time. The obvious problem here is that sound travels MUCH slower than light. Since nearly all meteors, even bright ones burn up between 80-110 kilometres high, any sound will reach you quite some time after the sighting. One possible explanation is electrophonic phenomena. This means that the meteor sound would be transmitted from nearby metallic objects near the observer such as wires. Some serious attempts have been done to better understand the exact nature of this intriguing process.

How to observe meteors
To observe meteors, choose a clear dark moonless night as far away from the city lights as you can. The darker the sky is, the more meteors you will see. Light pollution will greatly affect the number of meteors visible. The moon is also a major problem when it is visible, so plan accordingly. When choosing your site, make sure you get permission from the owners to use it. If you are going to observe along a random country road, go with a friend for the sake of safety. Let others know where you plan to go. Bring along emergency supplies in case things would go wrong (car phone, food, first aid kit). To make the session enjoyable and easier on your neck, bring a reclining lawn chair. Plenty of warm clothing will keep you warm. Always plan for 10 degrees colder than what it is supposed to be, even in summer. When lying still for long periods in an open field, you will get colder much faster. Take a break every once in a while and get up, to keep you active and alert. On cool nights, bring a thermos of hot drink. Music will also accompany you when meteors are slower to come.

How to contribute useful reports and learn more
With some basic knowledge, it is possible for amateur astronomers to actively contribute to real meteor science! You can contribute data that may be extremely useful for scientists to help better understand comets, our Solar System and even hints about our own existence! The International Meteor Organization (IMO) collects data from observers (mostly all amateurs) around the world. It has also standardized visual observing methods to ensure the most accurate data available. If you are interested to contribute to science (using the minimum of equipment), please take a look at the International Meteor Organization site or see the North American Meteor Network (NAMN) site. In recent years, the NAMN has launched an email discussion list called meteorobs, which has grown and become highly successful. Under the leadership of Lew Gramer, it has proved to be a fantastic way to report critical meteor shower events from all around the globe. I would recommend this email list to anyone who wish to pursue an interest to meteors. The background and knowledge from people on that list is almost endless. You can find more information about it on the NAMN web site.
For links to meteor organizations around the world, see our Meteor Links Page.

Good luck and many clear nights of "shooting stars",