Seasons in the Sun
by
Kamal Lodaya

If you watch the Sun over the year, you will see that the Sun rises and sets at different places on the horizon every day. In winter towards the south and in summer towards the north.

December 21 is called winter solstice, when the Sun rises and sets at its southernmost. After that sunrise and sunset move northwards. We say the Sun is doing uttarayana, moving towards the north. In December it is winter in the Northern hemisphere of Earth and summer in the Southern hemisphere, so we Northerners call it winter solstice. 

June 21 is summer solstice, when the Sun rises and sets at its Northernmost on the Tropic of Cancer, a circle at 23.5 degrees of latitude on Earth. After that sunrise and sunset move Southwards. This is called dakshinayana. In June it is summer in the Northern hemisphere and winter in the Southern hemisphere. Days are longer in summer and shorter in winter.

The Sun's position in the sky is divided into 12 rashis or signs of the Zodiac. Rashis are very old markers for dividing the Sun's path. These are specific constellations (groups of stars) in the sky. Each has many stars. For example in March and April the stars behind the Sun are from the Meena (Pisces) and Mesha (Aries) rashis. Since the Sun is so bright the stars in these rashis cannot be seen then. Which stars lie behind the Sun can be calculated by seeing the rashi that is highest in the sky at midnight and moving 6 rashis around.

Rashis were known to the Babylonians of today's Iraq in 1800 BCE. The names seem to have been finalized in Persia (Iran) in 5th century BCE. In India the oldest appearance of rashis is in Tamil Sangam literature in 3rd century CE. They are not found in the Mahabharata, completed around 4th century CE.

The apparent movement of the Sun from one rashi to another is called a sankranti. Since there are 12 divisions in a year of 365 days, sankrantis will happen every 30 or 31 days. March 14 is Meena sankranti and April 14 is Mesha sankranti. Mesha sankranti is the beginning of a new year in many Indian calendars. This calendar was written down in 499 CE by Aryabhata, living in Kusumapura (Patna in Bihar). Much later in the 19th century, Indian lawyer Bhimrao Ambdekar was born on 14 April.

Makara rashi sankranti (the date when the Sun appears to enter the Makara rashi in the sky) coincides with the festival of Uttarayana, Karka rashi sankranti (Sun on Tropic of Cancer, enters Karka rashi) with Dakshinayana. This year summer solstice (most daylight) happens on 21 June, but the festival of Dakshinayana is celebrated on 16 July. Winter solstice (least daylight) is on 21 December. Uttarayana is celebrated on 14 January, also marking the festival of Pongal in Tamil Nadu. Why this disparity?


Solstices keep changing
Very precise observations of bright stars, such as Chitra (Spica), were recorded by Egyptian observer Timocharis around 290 BCE. Egyptians had been observing the stars at least since the 25th century BCE. After Greek emperor Alexander conquered Egypt, the Greek empire absorbed a lot of their knowledge. Most likely Timocharis worked in the library in the Egyptian city of Alexandria, named after the former emperor.

Eratosthenes of Shahhat, Libya, lived later in the 3rd century BCE. Libya was ruled by Greece and the Greek empire had schools (a school was called a gymnasium). Eraosthenes studied and later became chief librarian at Alexandria. He became famous for measuring the circumference of Earth.

Eratosthenes pointed out another disparity in the Greek calendar of 365 days, that the seasons kept shifting. This shift was estimated as losing 1 day every 4 years. You may remember that Greeks used to have the Olympic games every 4 years since at least 7th century BCE, so the Greeks would have noticed the disparity.

Priests under the Egyptian ruler of that time, Ptolemy III, announced that every 4 years a leap (adhika) day would be added to the year. The Greek emperors may not have agreed and the idea was lost. Around 130 BCE, Greek astronomer Hipparcos, who lived in today's Turkey which was conquered by Alexander, compared the position of star Chitra (Spica) with that recorded by Timocharis 160 years before him on the same date, and exactly measured how the relationship of seasons with the stars changes. So he scientifically demonstrated that seasons keep shifting. After that, the leap day idea was added to the calendar by Roman emperor Julius Caesar.

After Isaac Newton in the 17th century we know that the rotation of Earth precesses, like a top whose axis keeps shifting slightly as it spins. This reason was not known to Hipparcos. But he observed the precession.

Calendar reform
The calendar had been corrected, but the seasons kept precessing, now gaining about 1 day every century. Prophet Muhammad gave a sermon at Mount Arafat in Arabia rejecting calendar reform by Julius Caesar and others, proposing direct observation of the lunar crescent to begin months. (The Sun and seasons are completely ignored.) He started the Islamic lunar calendar in 622 CE on the date of his migration from Makkah to Madinah, 16th July. This year, Islamic year 1446 is expected to begin on 7th July 2024, gaining 44 years since then.

Based on a proposal by Italian doctor Luigi Lilio, the Julian calendar was reformed by Pope Gregory XIII of the Roman Catholic church in the 16th century, to have three leap years less every 400 years. So 1600 and 2000 would be leap years, but 1700, 1800 and 1900 would not be.

To bring the festival of Easter to its traditional dates (and therefore also the solstices to June 21 and December 21), Pope Gregory took the extraordinary step of removing 10 days from October 1582. In India, the British rulers reformed their calendar by removing 11 days from September in the year 1752. This became an election issue in 1754, conservative British politicians claiming that the Catholic church was calling the shots over the Church of England.

Russia reformed its calendar in 1918. (So the October revolution of 1917 was in November according to the Gregorian calendar.) The Eastern Orthodox church of Russia now follows a reform suggested by Serbian climatologist Milutin Milankovitch. It has seven leap years less every 900 years: that is, after 2000 and 2400, the next 29th February in a century year will be in 2900 and not in 2800. This calendar is more accurate than the Gregorian calendar.

Indian panchanga makers did not participate in these reforms. They continue to follow Aryabhata's calendar plan. So the shift that had happened to the solstice dates keeps accumulating. These days we have our calendars and panchangas calculated on computers. The formulas which the panchanga makers use follow Indian calendar makers of the Gupta Empire in the 5th century CE.