Transform.RotateAround

Description

Rotates the transform about axis passing through point in world coordinates by angle degrees.

This modifies both the position and the rotation of the transform.

using UnityEngine;

//Attach this script to a GameObject to rotate around the target position.
public class Example : MonoBehaviour
{
    //Assign a GameObject in the Inspector to rotate around
    public GameObject target;

    void Update()
    {
        // Spin the object around the target at 20 degrees/second.
        transform.RotateAround(target.transform.position, Vector3.up, 20 * Time.deltaTime);
    }
}