Apex of the Earth's way?

Hi,

In the gaps between observing the transit, I've been trying to help a
chap calculate meteor radiant drift...

Does anyone know of a table detailing the apex of the Earth's way, and
ideally also the Earth's heliocentric velocity, on a day by day basis?
Failing that, a method for calculating the above?

Thanks and happy observing,
--
David Entwistle

David Entwistle wrote:

In the gaps between observing the transit, I've been trying to help a
chap calculate meteor radiant drift...

Does anyone know of a table detailing the apex of the Earth's way, and
ideally also the Earth's heliocentric velocity, on a day by day basis?
Failing that, a method for calculating the above?

Kepler's laws should get you close enough (though they aren't phrased
in the way you want, so there will be some maths involved).

Specifically the second law should give you the heliocentric velocity:
The line joining the planet to the Sun sweeps out equal areas in equal
times as the planet travels around the ellipse.

If you do a search on the net for "Kepler planetary motion" you should
find some background and hopefully a treatment which covers the
calculations you specifically want.


Tim
--
Love is a travelator.

In article , Tim Auton
tim.auton@uton.[groupSexWithoutTheY] writes

Kepler's laws should get you close enough (though they aren't phrased
in the way you want, so there will be some maths involved).


Thanks Tim,

I fear that may require more mathematical skill than I have at my
disposal at the moment. Although if I ever get sent to a desert island,
it'd be 'Astronomical Algorithms' that I take with me and a binocular,
as my luxury...

--
David Entwistle

JRS: In article , seen in
news:uk.sci.astronomy, David Entwistle
posted at Tue, 8 Jun 2004 10:46:43 :

Does anyone know of a table detailing the apex of the Earth's way, and
ideally also the Earth's heliocentric velocity, on a day by day basis?
Failing that, a method for calculating the above?

Well, ISTM that roughly the Apex ought to be on the ecliptic,
perpendicular to the line joining the observer to the dawn sun; and that
the speed will not vary much from 29.7 km/s.

ISTM that it would be useful to know the exact description of the
planetary orbits (etc.), not only in TLE form but also in elementary co-
ordinate geometry form, so that one could just insert the time and get
directly to the Cartesians of position and velocity.

I've said before that it seems of interest to have, in map-of-sky
displays, the ability to display angular momenta, to which I add
velocities (and any other vector quantities) overlain on or instead of
the positional display.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
I find MiniTrue useful for viewing/searching/altering files, at a DOS prompt;
free, DOS/Win/UNIX, URL:http://www.idiotsdelight.net/minitrue/ Update hope?

In article , Dr John Stockton
writes

Well, ISTM that roughly the Apex ought to be on the ecliptic,
perpendicular to the line joining the observer to the dawn sun; and that
the speed will not vary much from 29.7 km/s.

Thanks John,

Yes, I can see that being a workable solution based on the approximation
that the Earth's orbit is circular. It would be equivalent to the
tangent to a point on the circumference of a circle being perpendicular
to the radius at that point.

If I'm not mistaken, the approximation should hold true throughout the
day and the night, not just at dawn.


ISTM that it would be useful to know the exact description of the
planetary orbits (etc.), not only in TLE form but also in elementary co-
ordinate geometry form, so that one could just insert the time and get
directly to the Cartesians of position and velocity.

I've said before that it seems of interest to have, in map-of-sky
displays, the ability to display angular momenta, to which I add
velocities (and any other vector quantities) overlain on or instead of
the positional display.


I'd certainly go along with that. Solar longitude would be nice too. If
anyone knows of a software package with those facilities, then I'd like
to know.

--
David Entwistle

JRS: In article , seen in
news:uk.sci.astronomy, David Entwistle
posted at Wed, 9 Jun 2004 17:45:46 :
In article , Dr John Stockton
writes

Well, ISTM that roughly the Apex ought to be on the ecliptic,
perpendicular to the line joining the observer to the dawn sun; and that
the speed will not vary much from 29.7 km/s.

Yes, I can see that being a workable solution based on the approximation
that the Earth's orbit is circular. It would be equivalent to the
tangent to a point on the circumference of a circle being perpendicular
to the radius at that point.

If I'm not mistaken, the approximation should hold true throughout the
day and the night, not just at dawn.

True. I started with a mental two-dimensional diagram, intending to say
"overhead at dawn", realised that would be inconvenient to modify for
those away from the plane ... But the apex itself is manifestly
independent of the observer.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.
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