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DISPLAYING POSTS TAGGED: tilt (3)

Winter solstice

Author
by Martin Bush
Publish date
21 June 2012
Comments
Comments (3)

Martin is the programmer at the Planetarium at Scienceworks.

Today is the shortest day of the year, also known as the winter solstice. More correctly, it's the day on which the solstice fell, at 9:09am AEST.

Solstice means 'the Sun stands still'. Although we never see the Sun stop moving across our sky from east to west, it does stop moving in a south-north direction. Our winter solstice is the precise moment at which the Sun reaches its northernmost point in the sky, stops, then starts moving south again.

After the solstice, the Sun starts rising higher in the sky, and the points on the horizon where the Sun rises or sets start moving south.

Analemma Image of an analemma taken over the course of a year by Robert Price in Bethanga, Victoria, consisting of 48 images of the Sun superimposed on a single background image. The winter solstice occurs when the Sun is at the lowest point in this image.
Image: Robert T. Price
Source: Robert T. Price
 

Of course the Sun is not really moving south and north. Its apparent movement is a result of the Earth’s tilted axis moving around the Sun. On the winter solstice the axis is tilted away from the Sun, the Sun rises lowest in the sky and the sunlight's energy is the most diluted across the ground. You can learn more about the cause of the seasons in the Melbourne Planetarium show Tilt!

The day on which the solstice falls is the shortest day of the year, but not the day with the latest sunrise or the earliest sunset. This is because Sun time is not exactly the same as clock time.

At the winter solstice, Sun time is drifting later relative to clock time because the solar day is a little bit longer than 24 hours. For a few days after the solstice the small increase in the length of a day is not enough to overcome this drift, so the time of sunrise as measured by our clocks keeps getting later. Similarly the earliest sunset was a few days before the solstice.

Nor is the solstice the coldest day of the year. This is because of what is known as thermal inertia. It takes a lot of energy to heat up the ground and the oceans. At the moment the ground is still too warm to be heated by the amount of sunlight we are receiving, so it is continuing to cool. In around a month the balance will change. The ground will be a bit cooler and the sunlight a bit stronger, and the earth will start warming up again.

Links:

Infosheet: The Sun and the Seasons

Infosheet: The path of the Sun

Summer solstice

Author
by Tanya
Publish date
21 December 2011
Comments
Comments (0)

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.

summer solstice from Tilt 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.

Links

Session Times for Tilt

The Sun and the seasons

He's alive!

Author
by Brendan Williams
Publish date
17 May 2011
Comments
Comments (2)

This guest post is from Brendan, an animator and illustrator who is currently working on Tilt, the Planetarium’s upcoming show.

Here is Max’s first smile! After a process of design, approval, modelling, approval, etc. the characters for the new Planetarium show are starting to come to life!

Whilst it is a laborious and ongoing process, one that involves making a separate 3D model for each expression that the character will need, I can’t help feeling a bit of the exhilaration that Victor Frankenstein must have felt when his creature sat up and came in to being. Well, OK, that is a bit melodramatic but hey, I’m easily entertained (I wonder if that excuse would have worked for the doctor?)*.

Smiley Max Max with a grin!
Image: B. Williams
Source: Museum Victoria
 

There’s still plenty of work to be done, but it is these small victories that keep me excited and pointed in the right direction.

*before you all grab your pitchforks and storm the Planetarium Production Room, please note that Max and all associated characters exist only on in the computer!

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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