The mornings are getting lighter, as the days are getting longer. The promise of warmer weather is just around the corner and hayfever season is upon us. Welcome to Spring!
This Friday is the Spring Equinox. In truth, the equinox is a mere moment in time and this year it will happen at 7:04pm, 23rd September.
Of course, this means that the equinox will occur after the Sun has set in Melbourne. So what's so special about that time?
At 7:04pm on Friday 23rd September, the Sun sits on the celestial equator, the sky's equivalent to the Earth's equator. This year the equinox will occur when the Sun is below the western horizon.
Source: Museum Victoria
The equinox is the moment when the Sun crosses the celestial equator. Just like the Earth is split into two hemispheres by its equator, the celestial equator does the same, splitting the stars into those of the south and those of the north.
In fact the celestial equator is intimately linked with the Earth’s equator. Just pretend for a moment that the stars sit on a sphere surrounding the Earth. We call it the celestial sphere. Now take the Earth’s equator and push it off our planet and out into space – there you have it, the celestial equator.
So at 7:04pm, the Sun will cross the boundary between the northern and southern stars. We welcome it back to our hemisphere and as it returns our weather warms.
In the Sun and the Seasons you'll find more explanation of the link between the equinox and the seasons, along with the path of the Sun around the time of the equinox.
And there's one last thing to mention – the 23rd isn’t when day and night are equal. That was last Tuesday and the September Skynotes explains why.