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Re: Lyrid Meteor Shower Reminder
GeoZay schrieb:
> It's been a long while since anyone made a post about the upcoming
> Lyrid
> meteor shower. Just thought I would put the following in as a
> reminder. Useful
> Lyrid activity began yesterday (April 16). So far the long range
> weather
> prediction for S. California looks good. Hopefully I'll get a few
> hours of
> observing in prior to midnight and a few all nighters beginning this
> sunday.
> George Zay
>
> LYRIDS - This shower peaks on April 21/22 and produces 15 meteors
> per hour on average. Although the Lyrids are considered to be a
> major shower, I personally think of them as being a very active
> minor shower. The Lyrids are associated with Comet Thatcher 1861I
> and have produced several bursts of activity in the past. The most
> recent such event occurred in 1982 when the ZHR reached 90 meteors
> per hour. Begin your observations around 23 hours local. This year
> the moon will be a waning crescent and rising just before dawn.
> It is difficult to photograph the Lyrids due to their low numbers
> and only occasional fireball. I recommend a 50mm lens set at
> f/1.4-2.0. The Lyrids are visible from the southern hemisphere,
> but at a much reduced rate. Max: for 1998, April 21/22 at
> 10hr UT; ZHR: 15; Vel. 48km/s(Fast); Duration: April 16-25;
> Population Index: 2.9; Radiant diameter: 5 degrees; Train produc-
> tion: 17.2%; Radiant: RA 18h04m, Dec +34; Three Letter Shower
> Code: LYR
Dear List,
The first reports about the Lyrids date back 2000 years to old Chinese
chronicles. Comet Thatcher’s official designation is C/1861 G1 [BTW,
what’s the Iron Lady’s official designation? :-)] and has an orbital
period of more than 400 years ( a long-period comet). It’s interesting
to note that some meteor observers recognize a 12-year periodicity: 1922
- 1934 - 1646 and 1982 and blame Jupiter as the culprit. This year’s
peak is expected to take place in the early morning hours of April 22nd
for North America but it will be broad daylight here in Germany. As
George already stated they are pretty fast (30mps) but slower than the
Perseids (40mps) in August, their color is usually a bluish white and
their trains relatively short [even farther away from their radiant(s)].
In years, when there is no burst of activity, you may expect about 10
meteors per hour in a dark location with no serious light pollution.
1) Sky&Tel, April 1998, p. 95: The shower’s maximum rate is
unpredictable, having ranged from 5 to 90 meteor per hour (as seen under
ideal conditions) during the last 20 years.
2) Astronomy, April 1998, p. 70: You can expect to see only 8 to 14 per
hour, though higher rates have been noted in years past.
3) Astronomy Now, April 1998, p. 33: ... and could be expected to
produce up to 20 meteors per hour.
Explanation 1: Z H R = zenithal hourly rate
This is the number of meteors you would see in a dark sky if the
shower’s radiant were right over you at the zenith. The lower the
radiant is in your sky, the less meteors you will see. According to a
report by A.M. MacRobert of Sky&Tel (Aug. 1993, p. 49), there is a rule
of thumb: ‘You lose 60 % of meteors for every 1 magnitude of naked-eye
stars lost to moonlight or light pollution’ - in simpler words, if you
can only see the very brightest stars in your sky, don’t expect a
fireworks of Lyrids.
Explanation 2: R A D I A N T
Although shower meteors move in parallel orbits, they seem to ‘radiate’
from one point in the sky, or vice versa, if you follow their tracks in
the sky backwards, they seem to converge on a certain point in the sky
as a consequence of perspective. Remember railroad tracks (seemingly)
converging on a distant point.
Explanation 3: Of course, these words are not meant for George who will
know all these details. I thought of all those casual observers (who
might become serious meteor watchers one day) and who might wonder at
words like ‘radiant’ or abbreviations like ‘ZHR’.
Best wishes, Bernd
References: