The annual Lyrid meteor shower peaks this weekend on the night of April 21-22 when Earth passes through a stream of debris from Comet C/1861G1 Thatcher. The incoming Lyrid meteoroids have atmospheric entry velocities of 49 km/s, and Lyrid meteors appear swift. A fair proportion are bright, and some leave persistent ionisation trains.
The April Lyrid shower, while relatively modest, brings a welcome upturn in rates for a few nights, particularly around the maximum – this year expected just before dawn on Sunday, April 22 – normally producing observed rates of perhaps 6-8 meteors/hr under the clearest and darkest conditions when the radiant is well up in the sky, corresponding to a corrected Zenithal Hourly Rate (ZHR) around 10. Activity is about this level for 12 hours or so centred on the maximum. At other times, observed Lyrid rates may be only 2-3 meteors/hr.
The best observed Lyrid rates will typically be found after midnight, when the radiant (RA 18h 08m Dec +32°) located some 10 degrees south-west of Vega, near the Lyra/Hercules border, climbs higher in the sky. The radiant elevation approaches a very respectable 66 degrees by 0300 hrs local time.
This year’s peak coincides with a new Moon, so there will be absolutely no interference by moonlight. The promise of a good Lyrid display has prompted NASA to plan an unusual 3D meteor photography experiment combining observations from the ground, a research balloon, and the International Space Station. More details are available on:
Although Lyrid activity is generally rather modest, unmapped filaments of dust laid down by the comet occasionally trigger outbursts in rates – most recently in 1982 when, for a couple of hours, a ZHR around 200 was attained. While there is no expectation of enhanced activity in 2012, the Lyrids have sprung surprises on us in the past, and remain a shower very much worth observing.
John W. Mason, Director, BAA Meteor Section