Selecting Sphere Collider using a Tag

Unity Engine
1

I’m having issues selecting a Sphere Collider using a tag on the GameObject whose collider I want to use. I’m getting the following error:
“error CS0266: Cannot implicitly convert type UnityEngine.Collider' to UnityEngine.SphereCollider’. An explicit conversion exists (are you missing a cast?)”

Ideally what I want to do is select the SphereCollider in a scene of the object tagged as Planet. Is there a better way to do this?

private SphereCollider planet;			//collider for planet

	void Start () {

		GameObject sc = GameObject.FindGameObjectWithTag("Planet");
		planet = sc.collider;

	}
2 
planet = sc.GetComponent<SphereCollider>();

or

planet = sc.collider as SphereCollider;
3

Excellent! thanks so much. the first one worked.