Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring (or vernal) equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June (Northern Hemisphere) and December (Southern Hemisphere). Spring and "springtime" refer to the season, and also to ideas of rebirth, rejuvenation, renewal, resurrection and regrowth. Subtropical and tropical areas have climates better described in terms of other seasons, e.g. dry or wet, monsoonal or cyclonic. Cultures may have local names for seasons which have little equivalence to the terms originating in Europe. Meteorological reckoning Meteorologists generally define four seasons in many climatic areas: spring, summer, autumn (fall), and winter. These are determined by the values of their average temperatures on a monthly basis, with each season lasting three months. The three warmest months are by definition summer, the three coldest months are winter, and the intervening gaps are spring and autumn. Meteorological spring can therefore, start on different dates in different regions. In the US and UK, spring months are March, April, and May. In Australia and New Zealand, spring begins on 22nd or 23rd of September and ends on 21 December. In Ireland, following the Irish calendar, spring is often defined as February, March, and April. In Sweden, meteorologists define the beginning of spring as the first occasion on which the average 24 hours temperature exceeds zero degrees Celsius for seven consecutive days, thus the date varies with latitude and elevation. In Brazil, spring months are September, October, November. Astronomical and solar reckoning In the Northern Hemisphere (e.g. Germany, the United States, Canada, and the UK), the astronomical vernal equinox (varying between 19 and 21 March) can be taken to mark the first day of spring with the summer solstice (around 21 June) marked as first day of summer. By solar reckoning, Spring is held to begin 1 February until the first day of Summer on May Day, with the summer solstice being marked as Midsummer instead of the beginning of Summer as with astronomical reckoning. In Persian culture the first day