Why do Hindus take Pradakshina (Circumambulation) around sacred idols?
What does it signify? Do the number of times of taking rounds and direction matter? It would be great to know how it started and what it signifies.
To begin with, Pradakshina is not only done around idols in the Sanctum Sanctorum of temples, but also around many sacred things like Tulsi plant, Peepal tree, Agni, etc.
Now coming to your question, why do Hindus take Pradakshina (Circumambulation) around sacred idols?
Typically, Pradakshina is done after the completion of traditional worship (pooja) and after paying homage to the deity. Pradakshina is supposed to be done with a meditative mood.
We always assume God is the center of our existence. He also exists everywhere. So when we do Pradakshina or circumambulation, it signifies that our actions and thoughts are always centred around God. So, we are reminded of the eternal truth that God is the center of all things and is the main focus of our existence. This is the main principle behind Pradakshinam.
Do the number of times of taking rounds and direction matter?
In short, yes. In Pradakshina, one goes to the left hand direction to keep the deity around the Sanctum Sanctorum on one's right side (except during Pradhoshams when we do Pradakshina in a different way - Somasukta Pradakshinam). As a matter of fact, most of the planets revolve around sun in this way only.
Generally, Pradakshina is done once for Ganesha, thrice for Shiva, four times for Vishnu and nine times for Navagraha.
The clockwise pradakshina is applicable only in the Northern hemisphere of the earth. If one in the Southern hemisphere one must perform the pradakshina in anti-clockwise.
Likewise we are not supposed to sleep with head in the North side. In the Southern hemisphere one must not sleep with one's head to the South. It just makes the brain loaded with blood, makes it hyperactive and disturbs the sleep or worst one may die with brain hemorrhage.