Sunrise, sunset?

Question

http://aa.usno.navy.mil/cgi-bin/aa_rstablew.pl

I know this chart is probably not completely acurate, but when it says "Add one hour for daylight time, if and when in use," what does that mean?

Answer 1

During daylight savings time we turn the clocks forward.  So if the clock says 12, it was 11 before DST.  When you look at the chart and it says 11, you have remember that during DST it's 12.