Makar means Capricorn and
Sankranti is transition. There is a sankranti every month when the sun passes from one sign of the zodiac to the next. There are twelve signs of the zodiac, and thus there are twelve Sankranti's as well. Each of these sankranti's has its own relative importance but two of these are more important - the Mesh(Aries) Sankranti and the most important, the Makar(Capricorn) Sankranti. Transition of the Sun from Sagittarius to Capricorn, during the winter solstice in the northern hemisphere is known as Makar Sankranti. From this day begins the six-month long Uttarayana, considered very auspicious for attaining higher worlds hereafter.
Traditionally, this period is considered an auspicious time and the veteran Bhishma of Mahabharata chose to die during this period. Bhishma fell to the arrows of Arjuna. With his boon to choose the time of his death, he waited on a bed of arrows to depart from this world only during this period. It is believed that those who die in this period have no rebirth.