The last minute of 30 June 2015 will have 61 seconds, a phenomenon that is marked by the rotation and revolution of earth. A day on earth constitutes 24 hours which is denoted by hours, minutes and seconds. Hours, minutes and seconds are units of time. Time measured by earth’s rotation to the sun is called solar time. Solar time is further divided into apparent and mean time. Apparent time is measured by using a sundial which observes the movement of sun whereas mean time is measured by the relative position of the earth to the sun after every 24 hours. The clocks and watches we use in our daily lives are based on mean time.
Length of a second at present is based on the vibrations of caesium atoms in various atomic clocks. These clocks totalling 270 in numbers transmit signals to the International Bureau of Weights and Measures located in Sevres, France, which uses the signals to form the International Atomic Time. The times measured by these clocks are the most accurate. International Time i.e. Coordinated Universal Time (UTC) is used to accommodate the timekeeping differences between atomic and solar time. To adjust between atomic and solar time a leap second is being added since 1 January 1972 whenever necessary. Time will thus stop for a second on 30 June 2015 as the last minute will have 61 seconds. The addition is usually made in the last minute of either June or December.
The addition of an extra second is characterised by slow rotation of earth. The formula is based on leap year wherein an extra day compensates for the extra time of 5 hours, 48 minutes and 46 seconds that the earth takes over 365 days to complete one revolution around the sun. This data is fed in all computers and therefore web based services do not encounter a problem but the leap second phenomenon is not fed in computers since earth’s rotation is characterised by variation in the atmosphere and oceans, ground water, ice storage and so on and can change from year to year. Addition of a leap second three years ago affected major web services and one can expect the same thing this time around.