Sunrise times?

Question

what is the earliest time the sun can rise?

If was looking at the sunrise times for a specific country, and it changed form year to year. one year the sun might rise at 5am as it earliest time, one year the sun might rise at 4:30 am as it's earliest time. This must mean that the sun, in some part of the Earth is rising at the earliest time the sun can rise.

Does anyone know what time that is.

Answer 1

I guess the earliest time in theory is 1 second after solar midnight.

If you live on the Arctic circle (latitude 66.5607 N), then on the day of the Summer solstice (June 21), when the Sun's declination is 23.4393 N, it does not set.

It goes down, past west, past northwest, still going down, then as it reaches due north, it skims the horizon then starts rising again for the next "day".  To me, this does not count as a sunrise, since the Sun was never below the horizon.

On the next day, its declination will be a bit less.  At local solar midnight (the time when the Sun is due north), a part of the Sun will go below the horizon.  The next day, a little more, and so on.  Are these "sunrises"? It depends on the definition you use.

On some date (say July 6 -- it depends on a few local factors), when the declination of the Sun is equal to 23.4393 minus the apparent radius of the disk, minus the air refraction -- approximately 1 degree), it will finally set just before reaching due north:  the top of the Sun will barely get below the horizon for a few seconds, then peek out again and this is a sunrise (a few seconds after local solar midnight).

With the "beauty" of time zones, it could also be possible that such a sunrise occurs before it is midnight, standard time.  Imagine such a sunrise at 23:58 local standard time.  Would that make it the most earliest possible sunrise, or would this make it the most latest possible sunrise?

However, most places I know in the Arctic (including in Russia) keep a time ahead of the Sun (a.k.a. Daylight Saving Time), so I have never been to a place where a sunrise before midnight could occur.

But in the Antarctic (same thing around December 21), where there are no inhabited places, the rules for time-keeping are different...