When is spring in 2013?

Answer 1

Astronomical Spring begins on March 20 and ends on June 21 in 2013.

Astronomical spring in the northern hemisphere, as defined by the International Astronomical Union, begins with the Vernal Equinox on March 20, 2013, at 7:02 am EST. The equinox falls in the later hours of March 19 in the Mountain, Pacific and Alaska time zones of North America and across the Pacific Ocean between 120 degrees west longitude and the international date line. In the Southern Hemisphere, astronomical spring begins on September 22, 2012 in New Zealand, parts of Australia and Papua New Guinea and in the South Pacific west of the international date line and September 23 everywhere else.

At the start of the astronomical spring (spring equinox), day and night are approximately 12 hours long (at the equatorial plane) and the Sun is at the midpoint of the sky. Our north pole tilts towards the Sun.

NOTE: "The north pole tilts towards the Sun." That is true on summer solstice, but in December the south pole tilts towards the Sun. At the equinoxes the tilt is parallel to the Sun.

First Day of Astronomical Spring in the Northern Hemisphere:

In general, the four calendar seasons correspond to the relative position of the Sun to the Earth. Astronomical determination of spring is calculated according to when the Sun passes through the equatorial plane. When going from winter to spring, the Sun is moving north; as soon as the Sun crosses the equator, astronomers call it spring. (This applies to places north of the equator.)

First Day of Astronomical Spring in the Southern Hemisphere:

The astronomical ("official") date of spring south of the equator (corresponding to the first calendar day of fall in places north of the equator) would be around September 19/20, depending on the time zone when the Sun crosses the equator.

First Day of Climatological Spring:

Australia and New Zealand designate the first day of September as the "official" first day of spring. This corresponds to the date used by the World Meteorological Organization to define the climatological spring in the southern hemisphere. In the northern hemisphere, March 1 is the official first day of the climatological spring.

Ecological Spring:

Ecological spring is not a calendar based season, but rather begins locally with the beginning of the growing season when the mean daily temperature reaches 6 degrees C/42 degrees F. This can be as early as February in mild climates and as late as April or May in cool Climates.