Re: Newbie Question of The Day

From: Tony Beresford (
Date: Mon Jun 24 2002 - 04:18:23 EDT

At 14:27 24/06/02, Joseph Kern wrote:

>What exactly is an Epoch date?
For the TLE format the Epoch date has a dual role.
Most importantly is is the date and time defining when the satellite
is at the mean anomaly in the orbital elements. For historical reasons
this most often says when the satellite was at an ascending node, crossing
the Earth's equator from  South to North. 
A secondary property is that it defines the co-ordinate system for the
angular elements that define the orientation of the orbit in space,
as distinct from a fixed reference frame like J2000 or ICRF 2000,
which are based on the the positions of the equator and ecliptic
at jan 1, 2000. The precession of the Earth's axis of rotation
means the true of date numbers arent exactly the same. 
Tony Beresford

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