1) Celtic mythology encompasses the folklore and legends of the Celtic peoples across Europe, particularly in regions like Ireland, Scotland, and Wales. It features deities like Morrigan, Cernunnos, and Brigid, and delves into themes of nature, magic, and the heroic exploits of legendary figures like Cu Chulainn.

2) The development of the microprocessor by Intel in 1971 paved the way for the modern computer and led to the exponential growth of computing power.

3) The signing of the Magna Carta in 1215 laid the foundation for modern democratic principles and limited the powers of the monarchy in England.

4) The first commercial GPS (Global Positioning System) was launched in 1989 and provided accurate positioning and navigation capabilities to users worldwide.