Do you know the real date of due west sunset (hint - it's not the solstice..)

[cathalferris]

Something that I was thinking about recently, and that I confirmed through empirical use of planetarium programs, was a curiosity about the date of true western sunset and true eastern sunrise.

Taking the sunset to be the last sliver of the Sun's disc sliding below the horizon, it seems that this occurs due west on or around March 18th or so for UK latitudes, not as we have come to expect on or around March 21st. It can also vary a little with differences in local weather changing how atmospheric refraction behaves, and local altitude relative to the horizon altitude changing the horizon location both affecting the geometry of the sunset. It's mostly due to the atmospheric refraction raising the apparent Sun above the horizon.

I realise that this is being pedantic, but it's also quite interesting to me to see this behaviour.