Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
The mean observation duration per hour of day was 484±129 minutes (range 250–696 min). Shaded areas indicate hours before/after sunset. Note different scales of y-axes.
