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George wrote

> No, not the same at all, unless we are talking completely at
> cross-purposes.

Sorry, I have the impression we do. How would it be helpful now to discuss
this together in front of a blackboard! The only difference between our
views is to my oppinion how one would have to adjust for air pressure and
temperature, but let us forget this detail for the moment.

What George indicates with ...

>If that ray of light then carries on to disappear into outer space again,
>then (from symmetry) it would undergo a further deflection of 29 D1
>minutes, so in all 58 D1 minutes caused by the Earth. This is the total
>refraction the Earth would cause to that ray, as viewed by an observer far
>from the Earth.

... corresponds to twice the refraction for 0? altitude, this regardless
where the tangent point is above the earth's surface (air pressure and
temperature neglected), therefore:

R(0?)  +  R(0?)

>If the observer is at a height where the density relative to sea level is
>D2, and he was looking at a negative angle of A degrees, what is needed is
>the refraction  he would see if looking the other way, at a star at a
>POSITIVE apparent angle of 4 degrees, from a layer where the air density
>(relative to that at sea level) is D2. This is a familiar problem, with a
>well-known answer. Then that refraction needs to be subtracted from 58 D1
>minutes.

If the correction for air pressure is neglected, this corresponds exactly to

-  R(+4?)

And summarised now the refraction for an observer looking at an astronomical
object at -4?:

R(-4?)   approx. ? =  R(0?)  +  (  R(0?)  -  R(+4?)  )

To my oppinion this resulting refraction can in this case be corrected for
air pressure and temperature as indicated in the textbooks. To my
understanding it is the temperature and air pressure at the eye of the
observer which corrects/adjusts the complete line of sight.

Sorry, George, if I still should have not yet understood what you ment. In
this case I propose that the conference call with blackborad is soon
invented for the internet.

Cheers, Marcel

   

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