Saturday, 21 March 2015

Happy Equinox!

My memory is that the 21st of March is regarded as the Equinox;  Linguistically, that is the day when day and night are equal in length.  However it seems to not be quite right as according to one website sun rise is 0707 while sunset is 0714.  According to that site the closest to equal is 24 March with only 1 minute difference.  The entry in Wikipedia defines equinox as being when the sun is at zenith over the Equator and discusses a bunch of reasons why this doesn't exactly match the equal length idea.

Whatever: I am disinclined to let facts get in the way of a good(?) story and will assume that 21 March is the date of the equinox.  That being the case I have just been outside to try to get a photo of the sunrise at 0707 but we are behind a small ridge so it isn't here yet.  (The smell of woodsmoke from habitat reduction burns was clearly here.  Hopefully all national parks and nature reserves will soon have been incinerated to the satisfaction of the fire services and the smell will go away.)

Growing up in the UK this date also marked the start of Autumn.  In Australia the season officially starts on 1 March and my initial analysis of my weather data at a monthly level supported the idea of March being in Autumn for Carwoola.  In his most interesting book about seasons "Sprinter and Sprummer" Timothy Entwhistle puts the end of Summer as 31 March.  As March 2015 has had several maxima above 30oC it would fit my definition of Summer so I am probably in agreement with Tim.

Tim Entwhistle is a botanist so most of his examples are about plants.  With my basic interest being birds I find some support for the end of March from looking at that month being close to the end of migrant departure time as shown by this chart.
The orange squares represent the 'typical' last month in which species are seen in the area, and there are few left after March.

With regard to this March, most of the species expected in March are still around together with at least 1 Bronze-Cuckoo which might have been expected to have moved on.  The Noisy Friarbirds are beginning to appear in larger parties and the Tree Martins are forming large flocks.
So it is pretty business as usual.

No comments: