I’ve always loved summer – nothing beats the summer holidays, trips to the beach, warm sunshine and lazy summer evenings. But this year it means even more to me, because right now we are putting the finishing touches on a new planetarium show that opens on 26 December.
The summer solstice (22 December) is that day of the year when the Sun's path reaches its highest and longest across the sky. Our new show Tilt is a whirlwind adventure that describes how the seasons work.
In the new show Tilt, Kelvin (the robot) shows Annie and Max the long path of the Sun on the summer solstice.
Image: Melbourne Planetarium
Source: Museum Victoria
The changing seasons are so important to the way we live our lives. The summer holidays, the changing colours of autumn, the cosiness of winter and the blossoming of spring. And all this happens because our Earth spins on a tilted axis.
Without this tilt our days, year-in and year-out, would be the same. The Sun would always rise due east and set due west. The Sun’s path through the sky would be constant, reaching the same height every day. There’d also be 12 hours of daylight followed by 12 hours of night.
The tilt is what shakes this all up. Most importantly, the tilt varies the direction at which sunlight hits the Earth. Our warm days of summer occur when sunlight beams down most directly because our part of the world is tilted towards the Sun.
So enjoy the summer solstsice and the remarkable difference a little tilt on the world can make.
Session Times for Tilt
The Sun and the seasons
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.