<http://schema.org/alternativeHeadline>
"Two full moons in a single month, called blue moons, exist because the calendar months aren't perfectly synched up with lunar months."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mnn.com/earth-matters/space/stories/blue-moon-to-light-up-the-night-sky-this-week>