| AquilaDigital Partnership Home |  |
for use with Starry Night Pro
compiled by Stephen E. Hutson (
)
Download
Introduction
The R.A.S.C. Meteor Shower Radiant Database
The I.M.O. Meteor Shower Radiant Database
How to Use the Databases
About the Databases
More Information...
Revision History
[ Click here to search the site ]
Meteors are seen when the Earth happens across (usually) small bits of debris. These objects glow brightly as they encounter the friction of our atmosphere, and the result is a meteor, or “shooting star.”
Often, an increased number of these meteors will be seen — a so-called “meteor shower.” Most meteor showers recur on an annual basis, since it is believed that paths or trails of debris intersect the Earth’s orbit, and so we encounter particles from the same path or trail at pretty much the same time every year.
There are “sporadic” meteors, too; these are not linked to any known shower.
Many annual showers have been linked to orbiting bodies (comets and asteroids). It makes sense that something must be replenishing the debris trails that the Earth has been “cleaning up” year after year.
Meteor showers have a point in the sky (called the “radiant”) from which all of a given shower’s members seem to originate. If you were to draw a line backward in the sky from all meteors of a given shower, those lines would all intersect at or near that shower’s radiant. Note that few, if any, of a shower’s meteors will be seen right at the radiant.
The radiant is not static or fixed; it moves as the Earth moves in its orbit. The radiant positions included in the accompanying databases are given for the time of a shower’s peak activity (in epoch 2000.0 coordinates), and are provided to give the meteor observer some idea as to the radiant’s position.
The Observer’s Handbook of the Royal Astronomical Society of Canada contains a listing of several active annual showers. The below two images reveal the data that has been included from the R.A.S.C.’s Observer’s Handbook.
If you have configured Preferences->General to display “Get Info.” information in floating windows, the data will follow the format shown below:
If you have configured Starry Night Pro to show “Get Info.” data in non-floating (modal) windows, the data will follow the format depicted below:
After the meteor shower’s name will be found the Catalogue #, which is simply a sequential numbering of the meteor showers appearing in 2001’s Observer’s Handbook. The number is prefixed by “RASC-,” which simply stands for “Royal Astronomical Society of Canada.”
Name consists of the meteor shower’s common name. This usually — but not always — references the constellation containing the radiant itself.
Kind will always read “Meteor Shower Radiant.”
Magnitude will always be listed as “<unknown>,” since meteors vary widely in terms of brightness, within and between individual showers.
Peak (Solar Long) first gives the approximate date of peak activity, then the more accurate solar longitude. The solar longitude references the Earth’s position in its orbit at peak time, which is much less ambiguous than calendar times, which will vary from year to year.
The Rate (ZHR) heading gives the Zenithal Hourly Rate as listed in the Observer’s Handbook. You will probably see fewer than this number of meteors per hour, because the ZHR assumes an experienced observer, perfect sky conditions, and a radiant at or near the zenith (the point directly overhead). Moonlight will seriously degrade a shower’s performance, as will artificial lighting, haze in the atmosphere, and a radiant away from the zenith.
Days at >= 25% gives you some idea as to the shower’s duration and strength before and after the official “peak.” This is simply a listing of the number of days before or after the peak when the shower’s intensity drops to a level that’s about 1/4 the ZHR. If, for example, a shower’s ZHR is 100, and the Days at >= 25% is 5, then the ZHR 5 days before or after the peak would be 25 (25% of 100).
The Vel. (km/sec) heading indicates the approximate speed of the meteors in kilometers per second.
The Notes field may be blank (“-”), or it may contain interesting information about the shower — either from the Observer’s Handbook or from other sources.
All radiant location data is given for epoch 2000.0, which should account for what may seem like a small discrepancy between the Observer’s Handbook and Starry Night Pro’s position information.
The IMO (International Meteor Organization) provides a Meteor Shower Calendar at their web site. 2002’s Meteor Shower Calendar was compiled by Alastair McBeath and Rainer Arlt, and it contains a great deal of data about annual meteor showers in general, and about 2001’s showers in particular.
The Meteor Shower Calendar also contains a wealth of tabular data regarding annual showers, some of which appears in the “IMO Radiants (2002)” database. Some of that data appears in the below two graphics.
If you have configured Preferences->General to display “Get Info.” information in floating windows, the data will follow the format shown below.
If you have configured Starry Night Pro to show “Get Info.” data in non-floating (modal) windows, the data will follow the format depicted below:
Name consists of the meteor shower’s common name, which usually — but not always — references the constellation containing the radiant itself. In parentheses after the common name will be found the shower’s IMO code, which consists of three letters.
The Catalogue # begins with the prefix “IMO,” which stands for International Meteor Organization, and the showers are listed in order of occurrence throughout the year.
Kind will always read “Meteor Shower Radiant.”
The Magnitude will always be listed as “<unknown>,” since meteors vary widely in terms of brightness, within and between individual showers.
The ZHR item references the Zenithal Hourly Rate as listed in the IMO’s Meteor Shower Calendar. As indicated above (in the R.A.S.C. section), you will probably see fewer than this number of meteors per hour. Note that some of these showers are minor indeed; these make for an exciting challenge!
Solar Longitude (also known as “lambda”) indicates the Earth’s solar longitude at peak activity time. The solar longitude references the Earth’s position in its orbit at peak time, which is much less ambiguous than calendar times, which will vary from year to year. The item in parentheses — (Peak) — is the date of maximum activity, which is an approximate date (the Solar Longitude is more accurate).
Dates consists of the date range when shower members have been seen. Comparing values between showers will give you some idea as to how short — or long — the relative duration of the shower in question happens to be.
Population Index will give you some idea as to the ratio between bright and faint meteors for a given shower. The IMO’s Meteor Shower Calendar states it well: “The population index [is] a term computed from each shower’s meteor magnitude distribution. [A population index of] 2.0-2.5 is brighter than average, while [a population index] above 3.0 is fainter than average.”
The Velocity label — as with the R.A.S.C. listing (above) — indicates the approximate speed of this shower’s meteors in kilometers per second.
The Notes field contains data that is either from the IMO’s Meteor Shower Calendar or other sources.
All positions are given for the epoch 2000.0
The databases are already built-in to Starry Night Pro 4.0 and later.
Simply drag the “IMO Radiants 2002.ssd” file and/or the “RASC Radiants 2002.ssd” file to the folder entitled “Starry Night Data.” When you next launch Starry Night Pro, you will find the RASC and IMO databases listed on the “Display” floating palette.
The symbol for the shower radiants will appear as a very bright star (see below), to differentiate these items from actual sky objects. Meteor shower radiants are not sky objects at all, but rather are positions in the sky as described near the beginning of this document.
If the RASC and IMO objects do not appear in the same location, as shown above, it is because meteor shower radiants are not exact positions; they are based on many observers’ reports, and are continually revised and updated.
These databases were compiled by me, Stephen E. Hutson (), and I assume all responsibility for any errors the files might contain. I am an avid amateur astronomer and producer of a weekly astronomy program — The Sky Tonight® on our local community radio station, WEFT-FM.
I welcome any corrections, suggestions, or comments at the above e-mail address.
I have found these databases to be invaluable in my own meteor observing. You’ll quickly be able to determine how high a given radiant rises for any place in the world, and you’ll find that general meteor data from two highly-respected sources is simply a mouseclick away.
Thanks to Starry Night Pro for its intuitive, customizable interface.
I am deeply indebted to Ted Leckie and Mike Parkes of Space.com, who actively encouraged the uploading and distribution of these files.
A few web sites you might find useful (these worked as of 08 April 2002):
The Royal Astronomical Society of Canada
The International Meteor Organization
The American Meteor Society
Leonid Shower information
Sky Publishing’s info and links
The Meteor Group Hawaii
Gary W. Kronk’s in-depth information on specific showers
The North American Meteor Network
Astronomy Magazine
The International Dark-Sky Association
The Jet Propulsion Laboratory Home Page
The U.S. Naval Observatory
Enjoy!
Stephen E. Hutson
08 April 2002
16 May 1997: Original posting for Starry Night Deluxe.
05 July 1997: Updated IMO Data from the IMO’s 1998 Meteor Shower Calendar.
27 April 1998: Updated screen shots for compatibility with Mac OS 8.1.
26 December 1999: Updated datafiles and screenshots for 1999’s meteor data.
28 August 1999: Updated datafiles and screenshots for Starry Night Pro.
13 November 2000: Updated datafiles and screenshots for 2001’s meteor data; verified and updated URL listing.
08 April 2002: Updated databases for 2002’s meteor data, verified and updated URL listing, converted Read Me to HTML.
13 October 2003: Converted page encoding to UTF-8, and added note that these databases are included in SNP 4.0 and above.
24 January 2008: Converted page for HTML 4.0 compliance.
