Posted on: April 13, 2012
You’ve hopefully all enjoyed Easter, indulged in some sustainable Western Australian fish … and maybe a little chocolate. Some of you may remember that we had a particularly long weekend at Easter in 2011. This was because Easter Sunday fell on April 24th – the day before Anzac Day. This year, Easter Sunday was April 8th, whilst next year it will fall on March 31st!
How is the date of Easter then determined? Easter Sunday is the first Sunday after the full moon, following the Autumn equinox. Check out a moon phase calendar – and you’ll find that the full moon does not occur on the same date each month. As a result, Easter Sunday can actually occur anywhere from March 22nd through to April 25th.
What else does the moon dictate then? In ‘The Tide is High’ Lesson Plan, you’ll find out about the significance of the moon to the tide changes we experience. Tides are the rhythmic rise and fall of sea levels caused by the combined effects of the rotation of the Earth and the gravitational forces exerted by the moon and the sun. Thus, the change in the tide is responsible for your sandcastle being washed away, or not as the case may be, on the beach!
Here in Western Australia, King Sound near Derby, experiences the second largest tidal range in the world (after the Bay of Fundy in Canada). The Department of Transport have Western Australian tide times available on their website – www.transport.wa.gov.au/imarine/.
In Activity 2 of The Tide is High, students will experiment with cups or buckets of water to experience the gravitational pull and centrifugal forces between the Earth and the moon, in a similar manner to how high and low tides work.
As an extension to the activities in The Tide is High, if your school is located close to, or if students live nearby a beach, ask them to photograph it at the same time each day over a period of a week. Create a time series with the photos and ask students to predict whether it was high or low tide (or heading towards high or low tide). Use the tide charts available on the internet to confirm your results and if necessary, engage students in a discussion as to why their predictions may have been different from the tide chart.