Weather Glossary - Y
The interval required for the earth to complete one revolution around the sun. A sidereal year, which is the time it takes for the earth to make one absolute revolution around the sun, is 365 days, 6 hours, 9 minutes and 9.5 seconds. The calendar year begins at 12 o'clock midnight local time on the night of December 31st-January 1st. Currently, the Gregorian calendar of 365 days is used, with 366 days every four years, a leap year. The tropical year, also called the mean solar year, is dependent on the seasons. It is the interval between two consecutive returns of the sun to the vernal equinox. In 1900, that took 365 days, 5 hours, 48 minutes, and 46 seconds, and it is decreasing at the rate of 0.53 second per century. This decrease is due to the slow precession of the Earth's axis of rotation.
Parts of New South Wales have been warned to prepare for wild weather overnight as a low-pressure system from Tasmania gets set to batter northern parts of the state.
Three adults and two young children have been rescued by helicopter after becoming trapped in floodwaters in Huonville, south-east of Tasmania.
Power may not be restored to Eyre Peninsula homes until the early hours of the morning after twin tornadoes and wild weather caused significant damage to transmission towers in South Australia.