Shivaratri or the night of Shiva is related to the moon rather than the sun. The moon is symbolic of the human mind. The moon continues waning for sixteen days until it is left with only one-sixteenth of its power. The waned moon represents the mind whose powers have been diminished by whims and inconsistencies. It needs to be fed spiritual discipline to imbibe the divine spark. On Shivaratri, the mind should concentrate on the Almighty and thus gain control over itself again.
Another significance of Shivaratri is:
Shiva performs the cosmic dance, the Shiva Tandav. The dance is meant to attract all earthly creatures. When people are drawn to the Divine presence, they experience a spiritual cleansing. Their faith is strengthened and they are ready to merge with the Supreme Being. The Purusha and the Prakriti blend together on this dark night.
On this holy night, God invites man to take refuge in Him. Divine vibrations are plentiful on earth. At this time, people only need to meditate to be blessed with divine vibrations. When the mind is fixed on the Lord, it will experience the consciousness of the divine. This process is called Jagarana or nocturnal vigil.