On a moonlit stroll, a young man points to the cloudless sky and says, “Look—a full moon!”
His date is not impressed. “Technically,” she replies, “the Moon’s not full until 2pm, when its ecliptic longitude is opposite to that of the Sun.”
Hoping to save his pride, he replies, “But the Moon looks completely illuminated.”
“It’s never one hundred percent illuminated,” his date says, unfazed. She’s a tough cookie. “Oh, and on this side of the world it’ll be a corn moon.”
Pretending to check his watch, the young man gets confused. He remembers his science teacher explaining that the Moon reflects sunlight and that it is full when it is on the other side of the Earth from the sun, but the nighttime half of the Earth is on the opposite side of the Sun, so how could that be 2pm? Did the newspaper say it would be a full moon tonight, or did it say tomorrow night? And what’s a corn moon?
There’s only one thing he can do: look it up on Wolfram|Alpha!
One of the latest features added to Wolfram|Alpha is more coverage of full moons and other Moon phases. Back when people got their information from only a local newspaper, it was relatively simple to say that one night or another would be a full moon, because for a specific location, the time of a full moon would be closest to midnight on that day. But now it is easy to get your information from a newspaper that is far away, so its date can be off by a day. Of course, Wolfram|Alpha detects your location, so it is able to predict the date of the next full moon in your area, and the “Precise time” button reveals the exact time the full moon will take place.
Remember that because of time zone differences, there is always part of the world that is on a different day. And that affects labels like “corn moon”, which is the first full moon in September. The beginning and ending dates of September depend on the time zone, and sometimes the full moon is close to this boundary. The next ambiguous corn moon will be in 2012.
While moon phases are hardly the most complicated thing Wolfram|Alpha deals with, these examples show how it turns complicated and confusing queries into answers that are easy to understand.
Let me leave you with a word of advice. The next time you are on a midnight stroll, you might want to avoid looking like a show-off and instead explain that you found it out from Wolfram|Alpha.