Shukracharya did a severe penance for five thousand years to please Shiva and acquire the secrets of Mritasanjivani Viddya (bringing back dead person alive) from him.
When Lord Shiva did not appear even after such a tremendous penance, then he indulges himself in severest form of penance, by quitting having food and water. He now started living only on air. This continued for thousands of year.
Lord Shiva became very pleased with his penance. He manifested from the very Shivalinga, Shukracharya had been worshipping till now. He taught the secrets of ‘Mritasanjivani’ viddya to him and told him that by the help of this viddya he would become capable of making alive the dead persons. Lord Shiva also blessed Shukracharya to become a star and attain respectability among all the planets.
After blessing Shukracharya like this, Lord Shiva disappeared into the same Shivalinga from which he had appeared.