Gopashtami is observed on Kartik Shukla Ashtami day. In 2018, Gopashtami date is November 16. It is also known as Goshtashtami vrata.
On this day, Nanda Maharaj sent his kids Krishna and Balarama to herd the cows for the first time. Thus, on Gopaashtami day Krishna and his elder brother Balaram became qualified cowherds.
On Gopashtami day, Go Puja is performed. Cows are given bath on this day and decorated with colourful clothes and shawls and adorned with necklaces. Cows are offered special food offerings on Gopaashtami.
Gopashtami is celebrated with much gusto and enthusiasm in Krishna Janma Bhoomi Mandir in Mathura, Banke Bihariji Temple in Vrindavan, Guruvayurappan Temple in Guruvayur, Dwarkadish Temple in Dwarka, Shreenathji Temple in Nathdwara and all ISKCON Temples.
It is to note that some South Indian panchangs and calendars have referred this day as Goshtashtami.