Karka Sankranti 1910: Pomona, California

Karka Sankranti marks the Sun's transit into Cancer and the beginning of Dakshinayana, the Sun's southward course -- traditionally regarded as an especially significant Sankranti, with its own Punyakala timing rule (Ayan Sankranti) distinct from the other ten.

The exact moment the Sun crosses into Karka (Cancer) is called the Sankranti. The Punyakala is the auspicious window around that moment -- its exact length and placement (before or after the Sankranti, and how it is measured) follows a traditional rule that depends on which of the twelve Sankrantis this is; Karka and Makara Sankranti (the two Ayana Sankrantis, marking the start of Dakshinayana and Uttarayana) each have their own distinct rule, and the Vishuva (Mesha/Tula), Vishnupadi, and Shadshitimukhi Sankrantis each follow one of three other rules. Charity (daan), holy baths, and worship performed during the Punyakala window are traditionally held to be especially meritorious.