swill453 wrote:Not really. If it used the words "sunrise" (or sunset) specifically then it might have helped.
(Though of course I don't expect it could.)
Scott.
In that case you'd have to start with the
twilight definitions:
Civil twilight occurs when the Sun is less than 6 degrees below the horizon. In the morning, civil twilight begins when the Sun is 6 degrees below the horizon and ends at sunrise. In the evening, it begins at sunset and ends when the Sun reaches 6 degrees below the horizon.
Whether that's an apparent or a real sunset (i.e. the refracted image of the sun or the actual sun) is not stated, so agreed, not as helpful as I thought!
However, I did find this from the Hong Kong Observatory*:
For example in Hong Kong, the atmospheric refraction causes the sunrise and sunset to appear about 2 minutes early and late respectively when compared to the situation without the atmospheric refraction. In fact, the times of sunrise and sunset announced by the Hong Kong Observatory have already included the effect of the atmospheric refraction so that users do not need to calculate the times by themselves.Turning to the Greenwich Observatory** for a bit more help, I found the following definition:
The published times of sunrise and sunset refer to the moment when the Sun's upper limb, as affected by refraction, is on the true horizon of an observer at sea-level.Further, it seems (and makes sense) that there is a "standard" refraction that's built into the sunrise / sunset tables, which differs from the actual refraction on the day, which varies according to air conditions, affected by temperature, cold air inversions etc. so the observer can record a different time to that expected anyway.
It appears to have been a known issue for a while.
EVALUATING THE EFFECTIVENESS OF CURRENT ATMOSPHERIC REFRACTION MODELS IN PREDICTING SUNRISE AND SUNSET TIMES***
While the author of the table is unnamed, indications are that Newton is the origin of the 34' value.VRD
*
https://www.hko.gov.hk/en/education/astronomy-and-time/astronomy/00493-effect-of-atmospheric-refraction-on-the-times-of-sunrise-and-sunset.html**
https://www.rmg.co.uk/stories/topics/when-dawn-dusk-twilight***
https://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1776&context=etdr