The term Uttarāyaṇa (commonly Uttarayan) is derived from two different Sanskrit words – "uttara" (North) and "ayana" (movement) – thus indicating a semantic of the northward movement of the Sun on the celestial sphere. This movement begins to occur a day after the winter solstice in December, which occurs around 22 December and continues for a six-month period through to the summer solstice around June 21 (dates vary). This difference is because the solstices continually precess at a rate of 50 arcseconds per year due to the precession of the equinoxes, i.e. this difference is the difference between the sidereal and tropical zodiacs. The Surya Siddhanta bridges this difference by juxtaposing the four solstitial and equinoctial points with four of the twelve boundaries of the rashis. The complement of Uttarayana is Dakshinayana, i.e. the period between Karka sankranti and Makara Sankranti as per the sidereal zodiac and between the Summer solstice and Winter solstice as per the tropical zodiac. Difference between Uttarayana and Makar Sankranti There is a common misconception that Makar Sankranti marks the beginning of Uttarayana. This is because at one point in time Sayana and Nirayana zodiac were the same. Every year sidereal and tropical equinoxes slide by 50 seconds due to axial precession, giving birth to Ayanamsha and causing Makar Sankranti to slide further. When equinox slides it will increase ayanamsha and Makar Sankranti will also slide. This misconception continues as there is not much difference between actual Uttarayana date which occurs a day after winter solstice (of Dec 21) when the sun makes the northward journey, and 14 January. However, the difference will be significant as equinoxes slide further. In 272 AD, Makar Sankranti was on 21 December. In 1000 AD, Makar Sankranti was on 31 December and now it falls on January 14. After 9000 years, Makar Sankranti will be in June. Then Makar Sankranti would mark the beginning of Dakshinayana. However Makar Sankranti still holds importance in Hindu rituals. All Drika Panchanga makers like mypanchang.com, datepanchang, janmabhumi panchang, rashtriya panchang and Vishuddha Siddhanta Panjika use the position of the tropical sun to determine Uttarayana and Dakshinayana. Uttarayana in various treatises Surya Siddhanta Mayasura, the composer of Surya Siddhanta, defines Uttarayana, at the time of composition, as the period between the Makara Sankranti (which currently occurs around January 14) and Karka Sankranti (which currently occurs around July 16). Lātadeva describes this as half revolutions