The festival has astronomical significance: it marks the beginning of Uttarayana, the Sun's movement northward for a six month period. Uttarayana is considered auspicious, as opposed to Dakshinaayana, or the southern movement of the sun. All important events are scheduled during this period. Makara Sankranthi refers to the event of the Sun entering the zodiac sign of Makara or Capricorn.
Usually this day falls on January 14th or 15th in the Western calendar.
The festival is celebrated by boiling fresh milk early in the morning and allowing it to boil over the vessel - a tradition that is the literal translation for Pongal (in Tamil). People also prepare savories and sweets, visit each other's homes, and exchange greetings.