(meteorobs) Question about radiant drift

[Wayne T Hally]

No it is not exact, for 2 reasons. First, the geaocentric ("earth 
centered") position in the sky is a vector combination of the meteor 
stream's path and velocity, and our own path own around the sun. And even 
that in fact is not constant; for example we move faster near perihelion in 
January, and slowest in July when we are furthest from the sun, and the 
earth's orbit is an ellipse, not a perfect circle. So there is not 1 degree 
of solar longitude per day exactly.

Wayne

----------
From: 	Bamm Gabriana[SMTP:bamm at upastrosoc.org]
Sent: 	Sunday, June 06, 2004 4:56 AM
To: 	Global Meteor Observing Forum
Subject: 	Re: (meteorobs) Question about radiant drift

> This is a fact of our orbit. Any radiant that does not move 1
> degree per day along the ecliptic cannot be real, unless an
extrordinary
> explanation is available.

Hi Wayne,

Is this exact? I took a look at the data in Table 6 of the IMO
calendar, converted the RA and Dec into ecliptic coordinates, and
plotted them in a graph.

I expect that the change in ecliptic longitude is exactly 5 degrees
because the table is given every 5 days, but it doesn't seem to be
that way.

The rate of change in longitude seems to be slightly different for
each shower. In some cases the increase doesn't even seem to be
linear; the perseid radiant for example seemed to be gaining in speed
as the shower progresses.

I hope this is merely because the figures in the table are rounded
off to the nearest degree (and nearest day too, because they are in
terms of calendar days instead of sol). I wish I could have more data
so I can verify if this is indeed exact or if there is indeed a
numeric factor that depends on the shower.

Thanks and clear skies!

Bamm


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