Achala Saptami, also known as Saur Saptami, is observed on Magha Shukla Saptami, the seventh day in Shukla Paksh during Magh month. Achala Saptami 2018 date is January 24.
Achala Saptami festival is dedicated to Lord Surya. Devotees worship Surya Bhagwan on this day for better health and prosperity. Saur is another name of Surya bhagwan.
Achala Saptami is observed in a grand way in temples dedicated to Surya Bhagwan in North Indian states. Konark Sun Temple and Biranchi Narayan Temple (Biranchi Khetra) in Buguda, Ganjam district in Orissa, Modhera Surya Mandir in Gujarat, Martand temple in Jammu & Kashmir, Navagraha temples in Assam are some famous temples where Achala Saptami is celebrated in a jubilant manner.
There are some famous temples of Surya Bhagwan in Andhra Pradesh (Arasavalli Surya Devalayam in Srikakulam) and Navagraha temples in Tamil Nadu. In South India, Achala Saptami is observed as Rathsaptami.
Other festivals dedicated to Surya Bhagwan are – Bhanu Saptami, Mitra Saptami, Martand Saptami, Surya Saptami, Surya Sashti, Chhat Puja or Dala Chhath Puja.