# Re: GOES question

From: Bob Christy (rdc@zarya.info)
Date: Thu Feb 12 2009 - 19:16:46 UTC

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```"That's a good question" as they say. And the answer is "It depends"
...on the local time directly below GOES, the Sun's latitude when viewed
from the Earth, and where on the Earth the observer is stationed.

X-rays travel at the same speed as all electromagnetic waves - 300,000
kilometres per second in round figures.

The time difference depends mainly on the difference in the distance
between the Sun and the Earth, and the distance between the Sun and the
GOES.

Again, using round figures and dealing with the simplest case of a zero
inclination orbit at the time of an equinox, it will vary between
-36,000 kilometres and +49,000 kilometres in a 24 hour cycle, as GOES
moves along its orbit.

When it is local noon at the sub-GOES point, the satellite will see the
x-rays about 0.12s before they hit any point on the Earth. when it is
midnight, then GOES will see the x-rays about 0.16s after they first hit
any point on the Earth.

These are two simple scenarios, there are many other answers covering
the scenarios in between. And of course..... there are multiple GOES in
different locations.

Bob Christy

Thomas Ashcraft wrote:
> I have a math question for anyone here:
>
> The GOES satellites monitor X-rays from the Sun.  What would be the
> difference in time ( a matter of seconds?) between when solar x-rays
> hit the GOES sats and then hit the surface of the Earth?
>
> I hope the question is clear and if not I will re-ask.
>
>
> Thomas Ashcraft
> New Mexico
>
>
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