The only effect of choosing to use Daylight Saving Time (DST), which European countries recognize as Summer Time, is that all the sky event times are pushed ahead one hour.
One can learn about Daylight Saving Time, known in Europe as Summer Time, and also learn All about Time Zones and Universal Time.
Choosing to show eclipses causes both solar and lunar eclipses to appear on the calendar. Choosing to show equinoxes/solstices causes those four annual events to appear on the calendar as well as Earth aphelion and perihelion. Choosing to show Moon apogee/perigee causes the moon apogee, perigee, minimum and maximum declination, and ascending and descending node to appear on the calendar.
In its implementation of the Gregorian/Julian Calendar option, the calendar of the two that was used in the time period selected is used. Thus the dates between 1582 October 4 and 1582 October 15 do not exist.
The Indian Civil Calendar, which permanently corresponds to the Gregorian calendar, is made available to display under the Other Calendars option. The Persian Calendar, also known as the Iranian Calendar, is made available in a similar fashion for it is the most accurate of calendars. These calendars are included for the millions of people who use them regularly.
For the astronomers, the option to display a range of Julian Days (JD) is made available under the Other Calendars. Whenever this option is selected, the Julian Days corresponding to the beginning and end of the month shown in the previous dialog are used. This way, for example, if 2007 CE July were chosen at first and then the user switched to the Julian Day range option, the range endpoints originally appearing in the Julian Day range dialog correspond to 2007 CE July 1 and 2007 CE July 31
The days in the calendar which are in gray text are days from either the previous or following month, or days outside the Julian Day range. They are shown for convenience.
Special thanks to National Space Club summer intern Sumit Dutta for his valuable assistance in preparing the Sky Events Calendar (July 2007).
All astronomical calculations are by Fred Espenak, and he assumes full responsibility for their accuracy.
Permission is freely granted to reproduce this data when accompanied by an acknowledgment:
"Courtesy of Fred Espenak, NASA/GSFC"
For more information, see: NASA Copyright Information.