Late sunset in Boise?

Question

Sunset in Boise about 9:45 PM local on June 27, 2008. About 2200 ft elevation. Why is sunset so much later than back home (Virginia) or other places I have been in June (Orlando, West Virginia)?

Answer 1

Answer from 'mrw0113' is the right one, particularly with regard to 'Boise' being 45 minutes behind the standard time.

being at 43.75 degrees, its sunset meridien after the 6pm meridian, for summer solstice (June 21, when sun's maximum northward shift is 23.45d) is calculated as

Tan^-1{(Tan 43.75)(sin 23.45)}

=Tan^-1{0.95729174 X 0.39794863}

=Tan^-1{0.3809529}

=20.8544859 degrees

which @ 4minuts/degree

=1hr 23mnt 25 sec.

This, combined with mrw0113's figure of 45 behind the local standard gives a delay of

2hrs 8mnt 25 sec after the local 6pm.

Answer 2

There are two reasons:

(1) Latitude (primary reason)

The higher the latitude, the later the sunset in summer.  If you go far enough north, there isn't any sunset at all at this time of year.  Boise (latitude 43°40'N) is further north than Orlando (latitude 28°30'N) or Charleston, WV (latitude 38°20'N).

(2) Longitude (with respect to the time zone) (secondary reason)

If we observed solar time, the time of sunset would be the same time for every place at the same latitude.  But, we have standard time zones now.  Thus the time of sunset is only the same as solar time at the central meridian for the time zone.  Sunset will happen "early" for places east of the central meridian and will be "late" for places west of it.  Boise is in Mountain Time Zone, which has a central meridian of 105°W.  Since Boise is at longitude 116°15'W (or 11°15' difference), sunset will appear to happen 45 minutes later than at the central meridian.

Both West Virginia and Orlando are in Eastern Time Zone, which has a central meridian of 75°W.  Orlando is at longitude 81°20'W (or 6°20' difference) and Charleston, WV is at longitude 81°30'W (or 6°30' difference).  Thus Orlando's sunset appears to be 25 minutes late, and in Charleston, WV it appears to be 26 minutes late.

So, Boise's sunset will appear to be up to 20 minutes later than the other two cities just because of its location in the time zone, PLUS as much as 56 more minutes (later than Orlando) because it is further north.