This is an Environment Setting for use with EEP-enabled viewers such as the latest Firestorm or Second Life viewers. For more information on EEP, see the Second Life Wiki at
http://wiki.secondlife.com/wiki/Environmental_Enhancement_Project.
This is a single Daycycle composed of four skies and one water setting, designed to give the illusion of being very near the North or South Pole during the peak of summer. The sun simply marches around the horizon, never setting, although it constantly looks like it is about to set!
This Daycycle setting is suitable for use on your avatar for your own custom, portable environment, or for deployment on a parcel or region you own. As this is a Daycycle, the position of the sun will change as the SL day progresses, but there is no night (that's what "Midnight Sun" means!).
It's not particularly realistic
The sun just rotates along the horizon and never changes altitude, which might be the case if you're on the poles but for replicating the experience near the Arctic circle, this ain't it.