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(meteorobs) Re: 99 Perseids
Everone needs to take note that the 99 Perseids will reach maximum
activity on the night of Aug. 12/13 and not the usual 11/12. The hour of
maximum activity occurs 6 hours later per year on average for the
Perseids and in fact for most showers. What keeps them from truly
roaming
the calendar is the fact that leap year occurs every fourth year moving
the date of maximum activity back one full day or 24 hours. Using the
table below one would expect the traditional peak to occur near 10:00 UT
Aug 13 in 2000. But since this is a leap year one day will be added
before this date so in fact the traditional maximum will occur near
10:00
UT Aug 12 in 2000.
Since a year is 365.25 days, it is that quarter day (or 6 hours) that
really messes things up! The Earth encounters the Perseids at the exact
same place in its orbit each year. We need to remember that it takes
365.25 days to get back to that same point! This is the reason for the
6 hours shift each year and the possible shift in dates of the maximum
activity of any shower.
Asaf, as for the rising of the Perseids radiant from Isreal, it lies
directly on the northern horizon at dusk and slowly rises until it is
located high in the sky late in the morning. Perseid meteors can be seen
throughout the night from your latitude but of course rates will be low
during the PM hours. This is the time though that those famous "Earth
Skimmers" occur shooting upwards from the northern horizon and lasting
several seconds.
This is a great tuneup for the strong leonid display expected 3 months
later in November.
Clear Skies!
Robert Lunsford
Jennifer Lobdell wrote:
> This was some time ago, but I'll take another stab at this. So we'll
> assume that he meant August 1999, since Perseids August 2000 are a full
> moon event.
>
> >From http://www.skypub.com/sights/meteors/perseids/98preview.html and
> several other sources, from recent data give the new peak at 137.7 degrees,
> the traditional peak at 140.0 degrees and the newest (1997, 1998) peak at
> 140.3 degrees, all true J2000:
>
> Solar longitude 139.7000 at 1999/08/12 20:28:21 UT new peak
> Solar longitude 140.0000 at 1999/08/13 03:58:16 UT traditional peak
> Solar longitude 140.3000 at 1999/08/13 11:28:09 UT newest peak
>
> Note that the overall peak of the Perseids in 1997 was very broad, with ZHR
> over 75 from Solar Long 139.55 to 140.4 or 1999/08/12 16:45 to 08/13 14:00
> UT, more than 21 hours of great rates.
>
> Computations according to Astronomical Algorithms, Jean Meeus, 1991, and
> available at my web page at http://www.halcyon.com/gml/astro/
>
> Something I didn't compute was radiant rise time for Israel.
>
> Gregg Lobdell
> gml@halcyon.com
>
> Jennifer Lobdell
> jenlobdell@halcyon.com
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