Summer or daylight-saving time.The amount of the time shift varies, but one hour is the most common.

The standard time zones are centered on meridians spaced 15 degrees apart, resulting in 24 separate time zones. Standard time zone boundaries, which in theory, are on longitudes 7.5 degrees east and west of a standard time zone meridian, in practice meander to accommodate local centers of population and political borders. The stretching of these boundaries can allow a region to use a zone time far different from the zone time that corresponds to its longitude. Much of Spain, for example, which is west of Greenwich, uses the zone time whose meridian is centered 15 degrees east of Greenwich. Lastly, not all areas make use of the standard time zones, instead their time is offset some fractional part of an hour from a standard zone time. Parts of Australia, for example, are offset one half hour from standard zone time.


Luciano