Today is celebrated as the appearance day of Shree Radhikaji. Shree Radhikaji is the Anandatmika Shrusti (bliss giving power) of Shree Thakurji. She is the Ahladini Shakti of Shree Thakurji. The description of Shree Radhaji is found in Garg Samhita, Brahm Vaivarta Puran, Padma Purana, Skand Puran. But in Shreemad Bhagwat Mahapuran, Shree Radhaji's description is rendered secret.
"Nirasta Saamyatishayena Radhasa Brahmani Ransyate Namaha" 2.2.24 ShreeBhagwatam
Shree Radhaastami utsav was not celebrated by Shree Mahaprabhuji. Instead, Shree Gusaiji started the tradition of celebrating the Radhashtami Utsav.
Shree Radhaji's father is Shree Vrushbhanji and mother is Shree Kirtiji. Shree Vrushbhanji Gop and Shree Kirtiji did excessive penance. Due to thier Penance, Lord Shree Vishnu became satisfied and asked them to demand some boon from him. They both demanded the child like him. Due to this, Shree Vishnu gave the boon and Shree Radhikaji, who is the ardhangini of Shree Thakurji appeared in the family of Shree Vrushbhanji Gop and Shree Kitiji in Raval (village in Braja).
Shree Radhikaji was having the celestial beauty and due to this, all the demigods and gods came to do the darshan of Shree Radhikaji. Shree Radhikaji did not open her eyes for one year. Due to this, Shree Naradji came and tried to open her eyes through creating many stotras like Shree Radha Sahastranaam, Radhastaka, Radha Upanishad etc., but shree radhaji did not open her eyes. But when she heard the sound of Maadal (an instrument played when some divine celestial body takes birth) in Gokul on the occasion of appearance of Shree Krishna, she spontaneously opened her eyes.