Sandhya

Shiva Purana narrated an intersting link of the most revered Devis: Lord Brahma created Sandhya and Manmatha as his ‘Manasika’ or mind born children. He got infatuated with Sandhya and Lord Rudra chastised Brahma and the latter looked for an opportunity when Rudra might also be a victim of passion and Vishnu said that Maha Deva was above such temptations. Meanwhile Sandhya Devi who was ashamed of Brahma’s passion resorted to fierce Tapasya to Maha Deva for thousand years under the tutelage of Maharshi Vasishtha in disguise as Sage Medatithi as per Brahma’s instruction. Since there was no response from Shiva she got desperate and tried to jump into the Homa Kunda (The Sacred Fire-Pit) in the Yagna being performed by Medatithi. Shiva made his appearance as she desired that none on her clan should ever be a victim like Brahma, that she should be an example of chastity and her husband should never cast a lustful eye on another woman. Shiva granted her wishes and advised that she might now fall into the fire-pit thinking of a person whom she desired to be her husband in her next birth. Shiva further gave her the boon that she would be the daughter of Daksha Prajapati as Sati Devi and as the daughter of Himavan as Parvati Devi in her subsequent two births. Sandhya then leapt into the fire-pit thinking of Medatithi (Vasishtha) as the husband in the immediate next birth. The Prana Vayu or the Vital Air of Sandhya’s burnt body was carried to the Solar System and Surya Deva converted it into three parts as

1. Pratah Sandhya
2. Madhyahnika Sandhya and 
3. Sayah Sandhya 

or of the morning-noon-evening timings of a day. The Sages at the Yagna were wonder struck that Sandhya was re-born as a girl-child as named Arundhati and was married to Vasishta when she came of age and earned the examplary fame of chastity; the practice of Vedic weddings is followed by the visioning of the Arundhati Star on the Sky by the new-weds as a part of the wedding procedure till date.

http://www.shivshankar.in/episodes-related-to-shiva-and-parvati/