7th July: Double Sevens Day

Double Seven Day is a Japanese festival which celebrates the meeting of two mythological lovers, Orihime, a weaver, and Hikoboshi, a herdsman, who were separated by the Milky Way. They were allowed to meet only once a year, on Double Seven Day, which some Japanese placed at July 7, the 7th day of the 7th month. In some areas, this holiday is celebrated on August 7, which is nearer the traditional lunar date.

Some things you might not know about the number seven.

1. We all know that there are seven days in a week, but do we know why? There isn't an obvious reason connected to the movement of the earth around the sun or the moon around the earth. There are several theories, in fact. The creation story is one, where God made the earth in six days and rested on the seventh. Some scholars believe it was the ancient Babylonians who first came up with a seven day week, because they had rituals connected with the seven heavenly bodies; the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn, which would be carried out on different days. The deal was sealed when the Romans adopted it. Or it could be down to the moon after all - there are four phases: full, waxing, waning and crescent over the 28 day month.
2. There are seven colours in the Rainbow. Isaac Newton, who, by his own admission, was not able to distinguish colours particularly well, originally spotted five: red, Yellow, Green, blue and violet. He included Orange and indigo later to bring the number up to seven so it would correspond to the seven notes in a musical scale, the days of the week and the then seven known objects in the Solar System.
3. The Hindus believed that the human body had seven chakras (the word means wheel, or turning, or possibly vortex or whirlpool), or energy centres, aligned up the spine - root, sacral, solar plexus, Heart, throat, third eye and crown. Each of these is assigned a colour starting with red at the root and advancing through the spectrum to magenta or white on the crown. It has been noted by some scholars that each chakra has an endocrine gland associated with it.
4. Seven is the atomic number of nitrogen.
5. As well as in the creation story, seven crops up in the Bible quite a lot. Seven pairs of each animal in the ark; seven years of plenty and seven years of famine in pharoah's dream; the seven year jubilee cycle; seven baskets of leftovers after the feeding of the five thousand; seven seals in Revelation, to name but a few. You might not know that seven people commit suicide in the Bible: Abimelech, who asked his armour bearer to run him through with a sword; Samson, who died along with the Philistines when he made their building fall down; Saul fell on his sword; and his armour bearer was so grief stricken on seeing this that he fell on his sword as well; Ahithophel, who hanged himself when his counsel was not followed; Zimri, who, on seeing the city had been taken, went in to the palace and set fire to it; and the one we all know, Judas who hanged himself after betraying Jesus.
6. A seven sided shape is called a heptagon. A regular heptagon cannot be constructed using a compass and a straight edge alone.
7. Seven is the only single digit number to have two syllables. Unless you're counting Zero.
8. Being a seventh son is a good or a bad thing depending on which culture you belong to. In some European folklore, the seventh son of a seventh son has special powers of healing and clairvoyant seeing. In others, the seventh son will be a vampire or a werewolf.
9. In some languages, including German and Spanish, cats have seven lives rather than nine.
10. The numbers on opposite sides of a standard six sided Dice add up to seven, and it is also the most likely score when two six sided dice are rolled - a one in six probability.