These are 5 position alpha-numeric codes comprising the d series. All other level II codes and descriptors are approved and maintained jointly by the alpha-numeric editorial panel (consisting of CMS, the Health Insurance Association of America, and the Blue Cross and Blue Shield Association).
Alaska: Although Alaska enjoys a high volume of aurora activity, its cruises are not often mentioned as northern lights cruises. During the Alaska cruise season, it's rarely dark enough for the lights to be visible.
The northern lights (aka aurora borealis) are an amazing display of green and sometimes red light seen near to the magnetic north pole, and they're caused by CMEs. Their southern equivalent occurs near the south pole, and is known as aurora australis.