• The Royal Observatory Greenwich has a wide-ranging treasure trove of information on time & Astronomy.

Clocks

• British Horological Institute - packed full of materials and links

Sundials

• The Sundial Trail at the Horniman Museum in London, England a comprehensive information site from the British Sundial Society

• The North America Sundial Society

Time Research

• Compute Local Apparent Sidereal Time that is the actual time for your spot on the globe in relation to Greenwich. Outside the USA you will have to know your longitude (that's the East, West one!). Greenwich is at zero degrees Prime Meridian of the World.