The use of Calender has been known to the Indians centuries ago and it shows the depth of knowledge our great forefathers had in the areas of Astrology and Astronomy and how they were capable of tracing the movements of planets in our solar system without any technology. There are many references in old Tamil literature regarding commencement of Tamil new Year - April 14. The name of the Tamil month is some times the name of the star itself. (e.g. Chithrai is always the star on the Pournami of the Chithirai month).
Several Tamil Literary giants like Nakkirar (3rd century), Tholkaapiar, also a great Tamil grammarian, Illangovadikal (8th century), et. al made references to the start of Tamil month in Chithrai.
On the Tamil new year day, womenfolks , after taking head bath draw kolam/rangaoli at the entrance of the house and decorate the house and the Puja room with flowers, fruits, neem leaves, etc. They also decorate the entrance door and others with mango leaves. At the auspicious time they do puja and aarthi and after that take a sumptuous meal. Some go to the temple in the morning, others in the evening. This is done in the hope the current year will give them prosperity and peace of mind, besides, they will surmount the hurdles with considerable ease by God's grace. On this day countless families buy gold jewels so that they can save enough gold jewelry for their daughter's wedding in the future. This tradition has been around for a long time. In the past decade this practice has become so popular that gold jewelry shops entice the people to buy gold on Akshayathrithi day by way offering discount.
Chithrai month is closely associated with the following : Birth of Sri Rama in this month, Sage Valmigi wrote the Ramayana in this month, Lord Vishnu took the avatar of Matsyam (fish). Creator Brahma visited earth on the very first day of Chitrai.
The following worships assume significance in this month: Praying to God Bhairava on the day of Bharani Nakshatra, worshiping of Parvati (consort of Shiva) on Suklabaksha Friday, conducting Lakshmi Narayana Puja (good for the entire family), worshiping of Lord Ganapathy at home (to remove obstacles in the future and now), worshiping of procession deities of Muruga (Karthkaya) and his consorts on the temple premises of Thiruchendur, Tamil Nadu and visiting any of the six shrines (Aarupadai Veedu) dedicated to God Muruga for prayer and worship.
Chitra Pournami & Varusha pirappu are the most important festivals in this month. Famous Chithirai Thiruvizha is celebrated at Madurai Meenakshi Amman temple with devotion and Bhakti.
Wishing you all a very happy Tamil New Year 2018.