Complex sentence: The day marks the start of the Uttarayanam, the day of the Indic solstice when the sun purportedly enters the 10th house of the Indian zodiac i.e. Makara or Capricorn.
Split into simpler sentences: The day marks the start of the Uttarayanam. It represents the Indic solstice when the sun purportedly enters the 10th house of the Indian zodiac i.e. Makara or Capricorn.