What is the difference between a falling star, meteor and meteorite?
Each of these objects begins as a meteoroid which can be thought of as a piece of rock or space debris in orbit around our sun. If the object enters the Earth's atmosphere, it will heat up due to friction and become visible as a meteor. Meteors are often called falling stars or shooting stars. If this piece of debris is able to reach the surface of the Earth, it is then known as a meteorite.
Will there be any meteors visible from my house tonight?
Sure! Sporadic meteors appear year round throughout the night, and produce a handful of meteors each hour. They are meteors that arrive from random locations in the sky, and are not from recognized meteor showers. On the other hand, meteor showers occur at various times throughout the year and often produce dozens of meteors per hour. The showers are normally named for the constellation they appear to come from. A calendar of meteor showers visible each year is located on the NAMN home page. A more detailed version is posted each year on the home page of the International Meteor Organization (IMO).
Which direction should I watch to see the shower?
Meteors from a meteor shower will seem to come from a particular location in the sky known as the radiant. It is important to know where this is in the sky so that an observer will know when to watch. The calendar of meteor showers on the NAMN web page lists the position of the meteor shower radiants at maximum activity using right ascension and declination coordinates. More information on right ascension and declination can be found on the Astronomical League's Astro Note 11: Celestial Coordinate Systems web page.
What is the best time to watch for meteors?
You can watch for meteors just about anytime! If a meteor shower is not active, sporadic meteors will still provide some activity. Although they appear all through the night, they tend to be more numerous after midnight.
Meteors from a meteor shower generally do not become visible until their radiant has risen above the horizon. For most showers, this is after 10 p.m. Therefore, it is important for an observer to know where the radiant of a shower is located, and when it rises. Beginning observers often mistakenly report meteors from a shower whose radiant is still below the horizon.
What is the limiting magnitude often mentioned in reports?
The limiting magnitude is a measure of sky brightness and indicates the faintest star an observer can see. This directly affects how many faint meteors an observer will see. Poor limiting magnitudes are most often caused by light pollution and the moon. You will often see limiting magnitude abbreviated as "LM." It is usually determined by counting the number of stars within the boundaries of certain areas of sky, laid out by the IMO. For more information, see Chapter 2 of the NAMN Guide.
What is ZHR?
Often used in shower analysis, ZHR is the abbreviation for Zenithal Hourly Rate. It is the number of meteors an observer would see if the radiant was located directly overhead, the limiting magnitude of the sky was +6.50 and the sky was clear. These conditions are rarely met, so the ZHR tends to be higher than what an observer sees in reality. The use of the ZHR allows various observations from different locations to be compared to each other. Chapter 8 of the NAMN Guide discusses the ZHR in more detail.
I have seen the letter F and the abbreviation Teff mentioned in meteor reports. What do they represent?
[NOTE: What follows is a simplified explanation of F and Teff. For a further discussion, see Chapter 2 of the NAMN Guide.]
Portions of the sky may be blocked by buildings, trees or clouds. If any of these obstruct the area of sky you are watching (known as the field of view), it will reduce the number of meteors you see. To account for this, observers record the percentage of their field of view that is blocked, and include it on their report as the letter "F".
Normally, an observing period should be a minimum of one hour in length. Keep in mind that if you take a break during this period you must subtract this time from the observing period. Clouds moving through your field of view and forcing you to stop observing must also be accounted for in a similar manner. What is left, the time you spend actually watching the sky and recording meteors, is known as "effective observing time", and is abbreviated as "Teff".
I would like to begin observing meteors, what should be my next step?
There is lots of information online to help you get started observing. First of all, our handbook Meteor Showers and Their Observation: A North American Meteor Network Guide is available online. This NAMN Guide is also available free of charge from our Coordinator in electronic format.
Also available is a condensed article on what to record while observing, including blank forms to use for submitting reports. Both of these together will provide you with all the information you need to begin recording meteors.
We recommend you consider joining the International Meteor Organization. This is a more formal, organized group of observers from around the globe. They produce the bimonthly journal WGN which contains excellent articles on meteor science. More information on this organization can be found at their website http://www.imo.net/.
For other questions, or to inquire about free membership in the North American Meteor Network, contact our NAMN Coordinator, Mark Davis at meteors@comcast.net.
