Λυριδες - Lyrids (LYR) 16-25 Απριλιου (Μεγιστο 22 Απριλιου)

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πηγη imo.net

Active: April 16-25

Maximum: April 22 11h UT (λo = 32°32 (but may vary - see text))

ZHR = 18 (can be variable - up to 90)

Radiant: α = 271° δ = +34°

Radiant drift: see Table 6

v∞ = 49 km/s; r = 2.1

TFC: α = 262° δ = +16° and α = 282° δ = +19° (β > 10° S)

 

 

The λo = 32°32 timing given above is the 'ideal' maximum found in the most detailed examination of the Lyrids in modern times, published in 2001 by Audrius Dubietis and Rainer Arlt, drawing on IMO results from 1988-2000. However, the maximum time was found to be variable from year to year between λo = 32°0-32°45 (equivalent to 2009 April 22, 3h to 14h UT). Activity was discovered to be variable too. A peak at the ideal time produced the highest ZHRs, ~ 23, while the further the peak happened from this, the lower the ZHRs were, down to ~ 14. (The last very high maximum occurred outside the examined interval, in 1982 over the USA, when a short-lived ZHR of 90 was recorded.) The mean peak ZHR was 18 over the thirteen years examined. While generally thought of as having a short, quite sharp, maximum, this latest work revealed the shower's peak length was inconstant too. Using the interval that ZHRs were above half the maximum amount, the Full-Width-Half-Maximum time, a variation of from 14.8 hours (in 1993) to 61.7 hours (in 2000) was detected, with a mean value of 32.1 hours. The very best rates are normally achieved for just a few hours however. One other aspect of the analysis confirmed data from earlier in the 20th century, that occasionally, as their highest rates occurred, the Lyrids produced a short-lived increase in fainter meteors. Overall, the unpredictability of the shower in any given year always makes the Lyrids worth watching, since we cannot say when the next unusual return may take place.

http://www.imo.net/calendar/2009#aprjun

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