This is one of the ashta maha vartams told in skandha puranam. It is observed on the full moon day when the sun is shining in the vruchchika rasi that is in the month of karthikai(Mid Nov to Mid Dec).
Way of observing:
Getting up early in the morning on that full moon day, finishing the daily duties, one worships the form of shri uma maheshvara made of gold or silver, with various sacrad materials of worship and offerings. Later going to a temple one anoints the parvati-parameshvara with panychamrutam (fruits mixed with sugar) and other substances, salute with offerings and tAmbulam, pray the Lord making the gestures of salutations. Coming back home donating to the love hearted devotees of Lord shiva, one eats with them only once that day or may eat fruits and sweets along with them. The idol of the Lord umA maheshvara is given to a shivanyani.
One who observes this vrata sincerely, would get the material benefits of the world. Afterwards would get the liberation too. A sightless muni called dhiranabindhuobserving this vrata got beautiful eyes. A lady by the glory of this vratam revived her dead husband, gave birth to a child and got to reach shivaloka. vishnu following this vratam in krishnavataram got many children. brahma got married to gayatri, savitri, indra got the son jayantan, vashishtar received kamadenu for doing his yagnya, gautamar got the son sadananta maharishi, janaka got the daughter sita. A dumb minded person called sudharman, mocked by the people about his stupidity, observed this vratam in devotion. By the Lord’s blessing he got the grace of goddess sarasvati and he became a pundit. The king sindhusenan was chased away by the enemies. He observed this vratam as per the advise of saint agastiyar. On the Lord’s order kubera won back the kingdom for him and handed over to him. This vratam gets to the observer the wealth’s and takes to the path of liberation.