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Re: (meteorobs) Next major shower
In a message dated 11/29/99 11:17:11 PM Eastern Standard Time,
rendrag@earthlinkdot net writes:
<< I still don't know what's the meaning of this solar longitude with
respect to observing meteors. It evidentially tells you where to be at
the peak of the activity of a shower? I have all kinds of books from
basic astronomy to cosmology, astrometrics to relativity. I have quite a
large library. However no mention of solar longitude. >>
Robert --
In making predictions about forthcoming meteor shower activity we
unfortunately cannot go directly by our local clocks and calendars. The
problem is that our civil timekeeping system bounces around with respect to
the Earth's position in its orbit from one year to the next. Instead, we
need to specify the time -- unambiguously -- by the Earth's position
directly. Meteor astronomers attempt to do this by noting the ecliptic
longitude of the Sun as seen from the Earth (referred to as the equinox of
2000.0).
For the Geminids, the predicted peak of 18 hours UT on December 14th
apparently corresponds to that point in the Earth's orbit where the Sun is
appears at an ecliptic longitude of 262.3 degrees. Generally speaking, in
terms of actual clock time, the peak of the well-known/major showers moves
forward by about one-quarter of a day (6 hours) per year. Going by this
rule-of-thumb, in the year 2001, the Sun will arrive at ecliptic longitude
262.3 degrees at 6 hours UT on December 14, which combined with an almost-new
Moon would make for highly favorable viewing circumstances for the Americas
-- especially along the east coast.
-- joe rao
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