public class RotateAroundTest : MonoBehaviour {

    Vector3 point;

    // Use this for initialization
    void Start () {
        // initial position
        transform.position = new Vector3(0.0f, 0.0f, 5.0f);

        // center position (origin)
        point = new Vector3(0.0f, 0.0f, 0.0f);
    }

    // Update is called once per frame
    void Update () {
        transform.RotateAround(point, Vector3.up, Time.deltaTime * 50); 
    }
}