The times they are a changing!

By James Piercy

Earlier this summer I travelled to New Zealand to take part in the Dunedin International Science Festival. 

It was great fun, and I really wanted to tell people back at home what I was up to! It was hard to call home because when I was up they were asleep – my clock was 11 hours ahead of those back home. I also left the UK on a bright summers day but spent two weeks in the middle of winter. These differences are both due to the earth’s rotation as it spins around, and how it moves round the sun.

We use the sun to set our clocks, midday is when the sun is directly overhead. Because the earth is turning it will be overhead in different places at different times. It’s really only an historical accident that the world’s clocks are all based around the time in London. Greenwich Mean Time sets 12.00 noon as when the sun is overhead in Greenwich London. The other time zones move around the globe from there, dividing the earth up into zones. Add one hour to the time for every 15 degrees you move east, take off an hour if you move the other way. This means that Sweden is one hour ahead of UK time, China is eight hours ahead and in New Zealand it is lunch time 12 hours before England.

CC-BY-NC science made simple

Things are made slightly more complicated due to the fact that most countries change their clocks during the year to allow more daylight hours, and places which are near each other may choose to have the same time as their neighbours even if they should really be an hour ahead or behind. That’s why the lines on the map below aren’t straight, and I was only eleven hours ahead in New Zealand. It was ‘British Summer Time’ at home and the clocks had all been put forward an hour in March- they will move back again at the end of October. There are some places which are very close to the time zone boundaries, where a short drive can leave you having to change your clocks. There are even a few towns close to state borders in the U.S where technically you have two time zones right next to each other. Would you be late for lessons if you went to school here?

World_Time_Zones_Map

The Time Zones of the Earth CC-BY-SA TimeZonesBoy

But what about the weather? While I was there, northern New Zealand had the worst storms in a decade, while back home it was hot and sunny.

Many people believe that we have different seasons because the earth moves nearer or further form the sun. It is true that the movement around the sun isn’t a perfect circle, and we do move nearer at times, but this is not the cause of changes in our weather. In fact the earth is closest to the sun in January, when it is winter in the Northern hemisphere.

We know that the two hemispheres have their seasons at different times of the year, so it must be a difference between the two halves of the earth that is responsible for the effect.

The earth is tilted as it moves around the sun. This means that sometimes the northern side is pointed towards the sun and six months later the southern side is tiled towards.

CC-BY-NC science made simple

CC-BY-NC science made simple

The tilt of the earth hardly changes how close we are to the sun but it does affect how the sun’s rays reach the planet. The end of the earth pointed towards the sun gets more direct rays of light and stays in the light for longer than the other side. This hemisphere therefore gets more heat during the day and warmer weather. As we move around the sun this light intensity changes and we move through autumn, winter, spring and back to summer.

CC-BY-NC science made simple

CC-BY-NC science made simple

 

The change in time zone causes problems with jet lag, as you are used to being asleep when you should be awake. I struggled on the way out but found it easier coming home- I suspect this is down to the change in season. Arriving back in summer meant longer, brighter days which help reset the body clock quicker.

Curriculum Links

England

KS3 – Space Physics

  • the seasons and the Earth’s tilt, day length at different times of year, in different hemispheres

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Posted in Exploring Science, Physics