Re: [guide-user] Atmospheric refraction?

Bill Gray Aug 29, 2016

On 2016-08-28 17:18, rjvnyc@... [guide-user] wrote:

> Does guide correct for atmospheric refraction?

Yes, using a numerically integrated method from the _Explanatory
Supplement to the Astronomical Almanac_. (This is the reason the
Settings... Location dialog has entries for humidity, temperature,
and atmospheric pressure. The only place those are used in Guide
is in the refraction algorithm.)

> See: page 11 for a reference
> to the work of *Thorsteinn Saemundsson *on the topic

I used to use that method; see the 'reverse_refraction' code at

("reverse" in the sense that you use it to compute the refracted
altitude from the unrefracted altitude, instead of the other way
around.) The Saemundsson method is probably more than good enough
for rise/set times; you only need the more complicated numerically
integrated method if you're looking for sub-arcsecond accuracy.

-- Bill