Wolves don't actually howl at the moon. Wolves howl because they are nocturnal animals, and their howls are a form of long-distance communication. They point their heads toward the sky when they howl because the stance provides better acoustics to carry their voice.
The primary reasons that wolves howl include calls for the pack to gather, signalling a pack member's location, and as a warning to other wolves to stay out of the pack's territory. The high pitch and suspension of the notes wolves use when they howl allows the sounds to travel up to 6 miles in the forest and up to 10 miles across the treeless tundra. The howl's frequency increases during evening hours and when they begin to hunt at early dawn. Wolves also howl more often during the winter mating season than any other time of year. The howls of male wolves aid them in attracting mates because the sound carries the coding for their body size and degree of health. For instance, the howl of larger wolves has a deeper tone. The howls of alpha wolves also tend to have a lower pitch than other wolves in the pack, and they typically howl more frequently.