ALPO Meteors Section

2012 Major Meteor Showers (Class I)

The meteor showers listed above are the easiest to observe and provide the most activity. Particular attention should be noted to the time and moonlight conditions. All these showers are best seen after midnight. Some are not even visible until after midnight. Showers that peak with the moon's age between 10 and 20 days will be affected by moonlight and difficult to observe this year. While the time each shower is best seen remains much the same year after year, the moonlight conditions change considerably from one year to the next. We will post upcoming details of each major shower that is free from moonlight well in advance of their peak activity.

Activity Period: the dates when the shower is active and the observer can expect activity from this source.

Maximum: the date on which the maximum activity is expected to occur.

S.L.: the equivalent solar longitude of the date of maximum activity. Solar longitude is measured in degrees (0-359) with 0 occurring at the exact moment of the spring equinox, 90 at the summer solstice, 180 at the autumnal equinox, and 270 at the winter solstice. Scientists use this time measurement as it is independent of the calendar.

Radiant: the area in the sky where shower meteors seem to appear from. This position is given in right ascension (celestial longitude) and declination (celestial latitude). The radiant must be near or above the horizon in order to witness activity from a particular shower.

Velocity: the velocity at which shower meteors strike the Earth's atmosphere. The velocity depends on the angle meteoroids (meteors in space) intersect the Earth. Meteoroids orbiting in the opposite direction of the Earth and striking the atmosphere head-on are much faster than those orbiting in the same direction as the Earth. This velocity is measured in kilometers per second.

r: The Population Index, An estimate of the ratio of the number of meteors in subsequent magnitude classes. Simply stated: the lower the "r" value, the resulting overall mean magnitude of each shower will be brighter. "r" usually ranges from 2.0 (bright) to 3.5 (faint).

ZHR: Zenith Hourly Rate, the average maximum number of shower meteors visible per hour if the radiant is located exactly overhead and the limiting magnitude equals +6.5 (A very dark sky). Actual counts rarely reach this figure as the zenith angle of the radiant is usually less and the limiting magnitude is usually lower. ZHR is a useful tool when comparing the actual observed rates between individual observers as it sets observing conditions for all to the same standards.

Time: this is the time of night when meteors from each shower are best seen. Quite often the radiant will culminate after sunrise therefore the last dark hour before dawn will be listed. Daylight Saving Time (Summer Time) is used from March through October. These figures are also highly dependent on the latitude of the observer. The time listed is most precise for mid-northern latitudes.

Moon: the age of the moon in days where 0 is new, 7 is first quarter, 14 is full, and 21 is last quarter. Meteor activity is best seen in the absence of moonlight so showers reaching maximum activity when the moon is less than 10 days old or more than 25 are much more favorably observed than those situated closer to the full moon.

Class: A scale developed by Robert Lunsford to group meteor showers by their intensity:

Class I: the strongest annual showers with ZHR's normally ten or better.

Class II: reliable minor showers with ZHR's normally two or better.

Class III: showers that do not provide annual activity. These showers are rarely active yet have the potential to produce a major display on occasion.

Class IV: weak minor showers with ZHR's rarely exceeding two. The study of these showers is best left to experienced observers who use plotting and angular velocity estimates to determine shower association. Observers with less experience are urged to limit their shower associations to showers with a rating of I to III. These showers are also good targets for video and photographic work.