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Re: (meteorobs) What's the best time to watch a shower?
When a radiant is on the horizon, meteors can be seen anywhere in the sky.
It is just like when the Sun is on the horizon. The sunlight doesn't stop
at the zenith.
The curvature of the Earth does have a slight effect however and again,
sunlight can be used as an analogy. The morning twilight glow starts when
the Sun is well below the horizon. Light from the Sun reflects off the
atoms and molecules in the upper atmosphere. The curvature of the Earth
allows this. With meteors, the curvature also results in this asymmetry
with meteors visible only in the direction of the radiant when it is below
the horizon. This is an effect separate from zenithal attraction, but of
course, zenithal attraction must still be applied in determining the
radiant elevation.
In most cases, the rates would be so low as to be unobservable, but from
places in western Asia or Europe, it may be possible to witness Leonids
with the radiant up to perhaps six degrees below the horizon, by looking
low in the direction of the rising radiant. You would only see Leonids if
the rates were very high, but this is the chance this year.
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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