N. Jameson, of Lower Hutt, asks :-

Why is the number 13 considered unlucky?

Duncan Steel (duncansteel.com), an expert on calendars, replied.

Fear of the number 13 is called triskaidekaphobia. There are various theories regarding its origin, but these are culture-specific. That is, different civilisations have contrasting superstitions regarding which numbers are lucky, and which are unlucky.

For example, many people from East Asia (China, Japan, Korea) believe the number eight to be propitious (octophilia), and the Beijing Olympics were planned to begin on the date 08/08/08. On the other hand, four is a number to be feared (tetraphobia), apparently because it sounds very much like the word for death. For Cantonese speakers, 14 and 24 are even worse, again due to the unfortunate links with those numbers’ pronunciations.

The number seven is considered lucky in many different cultures, and happens to turn up again and again in mathematics and science in various peculiar ways.

In ancient Judaic tradition seven was regarded as being important, and during the Exile in Babylonia that belief was reinforced by the coincidence with the Babylonians’ astrological week based on the seven known ‘wanderers’ in the sky – the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn – the Jews bringing that back on their return to Egypt/Palestine/Judaea. After the Romans conquered Egypt, they gradually adopted the seven-day week, supplanting the eight-day week they had used previously. It is from this that we derive our seven-day cycle with the days named for different planets.

One idea regarding 13 being unlucky derives from another calendrical point. The Romans considered February to be an unlucky month, and especially misfortunate was a 13th month of the year sometimes added at the end of February by the whim of the consuls. This month was called Intercalarius. Such an adjustment was required because a solar year contains twelve lunar months plus 10 or 11 days.

There have been other suggestions as to why some people think 13 unlucky. A favoured explanation is that Judas, the disciple said to have betrayed Jesus Christ, was the last (hence 13th) person to sit at the Last Supper, but this idea dates from not much more than a century ago.

There is evidence that the Babylonians thought 13 to be unfortunate, even 3,800 years ago, and also that the Vikings regarded 13 as a number to be avoided.

In the USA I have stayed at hotels lacking a floor 13, and also have seen house numbers listed as 12, 12A, 14, etc. The Belgian company Brussels Airlines altered its 13-dot logo in 2007 because it was causing negative feedback from customers. In Ireland, car registrations for the year 2013 were amended such that they would not begin with 13 alone.

Cricket is a game full of superstitions about numbers. Australian cricketers think of 87 as being unlucky, perhaps because it is 13 short of a century. English cricketers, though, get fidgety about 111, which is termed ‘Nelson’ (my home town), and I’ll leave the reader to look up why that is.