Vernal Equinox: Swallows return

September 27th, 2011
by Jo Law

The 2011 September equinox occured on 23rd September at 09.04UTC at which time the sun is observed directly overhead on the equator. On this day, it is the Autumnal equinox in the Northern Hemisphere and it is a public holiday in Japan.

Equinoxes are two moments in time when the sun crosses the imaginary celestial equator. At the March equinox the sun passes from south of the celestial equator to north marking the ecliptic meridian; correspondingly, at the September equinox the sun is at 180º on the ecliptic. The two distinct days in a year when day and night are closest to being of equal length are called equiluxes. In 2011 in Wollongong, the September equilux occurred on 21st September when the sun rose at 05:49 and set at 17:50, 12 hours and 1 minutes apart.

On Sunday 25th September, Bellambi AWS (Australian Weather Station) recorded the monthly highest rainfall of 64.8mm to date. The rainfall of this single day was more than the mean September rainfall (from 1997-2010) of 58.1mm.

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