Precession - procession

Do not make the typing mistake of writing precession when you mean procession, nor vice-versa - both words exist, and a spell-checker will not recognize that you are in error. (The error is not new: OED records precession for procession as far back as 1400, and up to 1600. It was commented on by Umberto Eco in 1993.)

• Precession, which is derived from the same root as 'precede', is a word you are unlikely to meet outside the fields of astronomy and physics. It refers originally to the apparent moving of heavenly bodies backwards, or in an anti-clockwise direction, against a more obvious forwards, or clockwise, direction of the daily 'motion' caused by the rotation of the Earth. This is now applied to similar phenomena in bodies other than the Earth, some other heavenly bodies and others more local, for example a gyroscope or spinning top. It is even used for the 'spin' of a subatomic particle.
  • In the case of the Earth, the phenomenon was first observed by the ancient Greeks, who noticed that the date of the equinox varied slightly from one year to the next. This is caused by a 'wobble' or precession in the axis of rotation of the Earth, which describes an approximate circle around the pole of the ecliptic once in about 25,800 years. The phenomenon is most fully labelled the precession of the equinoxes. It helps to explain why the positions of the stars observed by astronomers do not match the 'houses', or signs of the Zodiac, postulated by astrologers.
• A procession, which is derived from the same root as 'proceed', is 'a ceremonial or formal assembly or group of people moving forwards to mark some event'; 'a parade'. It has been extended to mean a moving forwards of boats, cars or other vehicles for the same ceremonial marking of the importance of an occasion.
  • In Theology, it has one or two other meanings, basically top do with hymns or other forms of worship uttered during a religious procession.
  • In sports journalism, a procession can be one of two (perhaps more) things, both of which imply humiliating defeat:
    • a race (of women, men, boats, horses, cars, etc) in which the competition is quickly over over and the winner clear long before the finishing line is reached;
    • in cricket, a rapid succession of batsmen coming out of the pavilion to start batting, and rapidly being beaten by the other side and returning to the pavilion.