What is the difference between Authority and Power?

[Idaho]

well Authority you have the rights to control. Power you have the ability to control.

Wording and refinements aside - that is basically it.

Authority has (some sort of) justification. Power is merely power, regardless of justification. The two are related, but often seperated.

I recognise the power behind the US' foreign policy, but I don't accept the authority of it. AQ groups claim authority from religious justifications, the US from ideological ones.

The UN is a classic example of authority with no power. With a continual lack of power, bodies slowly loose authority.