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Updated February 14, 2004
Lyrids: April 16-25; Peak 2003 April 22, 17h UT
After a flurry of activity that sees the Perseids, Orionids, Leonids, Geminids, and Quadrantids in less than four months, a dry spell of similar length ensues before the next significant meteor shower, the Lyrids of late April. A shower of great historical significance, the Lyrids yield moderate observed rates of roughly ten per hour most years, although occasional outbursts of higher activity make this a shower worth monitoring.
The Lyrids are thought to be a very old meteoroid stream due to the fact that particles have spread out through the entire orbit, albeit somewhat unevenly. According to Gary Kronk’s seminal book Meteor Showers, a significant outburst occurred in 1803 (~700 meteors per hour), and activity on the order of 100 per hour was observed in 1850, 1922, 1945 and 1982. As no two intervals are the same or even share common factors, there is no obvious orbital period embedded in these dates. Kronk concludes "it might be possible that the Lyrid orbit contains several irregularly spaced knots of material that could make it impossible to arrive at an accurate period based on visual observations." There is also strong disagreement between results of photographic and radar data, suggesting that more observations using different techniques will be of value.
The Lyrid meteoroid stream is steeply inclined at an angle about 80° to the ecliptic, which results in a fairly sharp peak each year. The shower has been associated with Comet Thatcher (1861 I), whose orbit came within 0.002 AU of Earth's orbit, specifically its position as of April 20. The stream’s orbit crosses the ecliptic plane at two points, called nodes, which are located near the orbits of Saturn and Earth respectively, suggesting that the gravitational influences of the planets have affected the orbital evolution of the stream. That said, due to its high inclination the orbit is now extremely stable with evidence of the Lyrids having been traced back to 687 B.C.E. Earth is located at the descending node, meaning the meteors rain down from the north, thereby favouring observers in the northern hemisphere. As Earth moves through the stream, the radiant point appears to migrate about one degree eastward per day, which is indeed typical of all meteor showers.
A waning gibbous moon will be nearing third quarter phase as the shower nears its maximum in the pre-dawn hours of Tuesday, April 22. While it will significantly hamper observations in the morning hours normally favoured for meteor observing, the Moon will be situated far in the south and will therefore not rise until 3:40 a.m. The radiant of the Lyrids is fairly close to the bright circumpolar star Vega (alpha Lyrae), and will have achieved 30° altitude by midnight and 60° by moonrise, providing a decent observing window in 2003.
The Lyrids are not considered to be a strong radio shower despite the favourable position of the radiant, which at +33° declination is above the horizon for more than 20 hours, similar to that of the Geminids. Although Lyrid rates are 85% lower, they should display a very similar diurnal rise and fall as the Geminids.
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