The Prime Meridian at Greenwich, London is the reference for every time zone in the world.
What is Greenwich Mean Time (GMT)?
United Kingdom is now on GMT
Which were the longest and shortest days?
The dates for equinoxes and solstices in the Northern and Southern Hemispheres are the same, but in opposite seasons. Autumnal/fall Equinox north of the Equator is mirrored south of the Equator by the Spring Equinox.