Generally the Sun is in the Capricorn constellation from 21st December to 20th January, although depending on the year the Sun can move into Capricorn either a day earlier or later. The Sun moving into Capricorn marks the Winter Solstice.
Ruled by Saturn, the planet of caution and restraint, Capricorns are resourceful and persevering with a strong sense of duty. They believe in tradition and order and therefore distrust the untried and untested - they need to learn to lighten up and relax.