The letter E appears twice in the word week but only once in the word year.. People can be tricked by focusing on trying to identify an event that happens twice during the span of a week but only once during the span of a year. However, the riddle's answer actually refers to the frequency with which the letter E appears in each of the two words. A similar riddle is: What occurs once in a minute, twice in a moment and never in one thousand years?. The answer is the letter M..
The first full moon was spotted on 1 July and the second will appear on the last day of the month â Friday, July 31. This appearance is the first such occurrence in three years since the last blue moon month in August 2012, the next will not be until January 2018. Astronomers predict it will only happen on 12 occasions between now and 2043.
The successful Apollo 11 moon landing on July 20, 1969, ushered in an era of moon exploration that has so far gone unrivaled. (Find out about NASA's plans to return humans to the moon in Naked Science: Living on the Moon, which premieres Sunday, July 19, at 9 p.m. ET/PT.)