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The Sun

One fine Saturday afternoon in October Sam and his friends go onto the beach to do some sketching. They have promised to pack up just before sunset so they can all be back at the Lighthouse for tea before it gets dark.

Sam is making some drawings of one of the crabs in a tidal rock pool, but Thomas has just got a new drawing program for his iPad and wants to experiment with it, so he draws something very simple and easy, just a view from the beach.

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This gives Sam an idea. He asks everyone to make a very simple drawing of what the beach will look like at sunset. They all draw something like this.

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Sam laughs.

“What are you laughing at?”

“Well, every single one of you has drawn the Sun going round the Earth!”

It’s true, every man woman and child who has ever lived has watched the Sun going round the Earth, but today almost every man woman and child alive ignores what they can see and believes what they are told, that the Earth goes round the Sun. There is a reason why they are told this, which is given on the Page on Astronomy after 1600 (under construction), but it is not because it explains the way we see the Sun move. The Sun rises and sets not because the Sun is going round the Earth, or even because the Earth is going round the Sun, but because the Earth is rotating on its axis.

When they are back at the Lighthouse Sam gets out a small globe. The Earth rotates on its axis, a line between the North and South Poles. If we look down on the Solar System from a point above the Earth's North Pole this is what we shall see, with the Earth rotating anti-clockwise, both on its axis and round the Sun.

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If however we look at the Solar System “edge-on” this is what we see.

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The Earth’s axis is tilted at an angle of 23.5° to the plane of the Earth’s orbit round the Sun, and this affects the way the Sun’s heat and light reach different parts of the Earth’s surface as the Earth moves round the Sun - it gives us Winter and Summer, and when it is Winter in Britain it is Summer in Australia. Where you live affects how you see the Sun and Moon and stars and planets.

We divide the Earth’s surface into a number of regions, separated by the Arctic Circle, the Tropic of Cancer, the Equator, the Tropic of Capricorn and the Antarctic Circle - Sam shows his friends these lines on the globe. They all live in the region between the Arctic Circle and the Tropic of Cancer (as do most Europeans, Americans, Chinese and Japanese) so it is their view of the Sun and Moon and Night Sky that Sam tells them about and explains.

Sam asks Harry to be the Sun and Adam to be the Earth. In the middle of the day the Sun is due South and at its highest point in the sky. Adam stands about 2 m from Harry and faces him. He stretches out his arms and Sam puts a card with an E for East on it in his left hand and one with W for West in his right hand. Adam says he thought West was on the left, but Sam says that is on maps, which today are usually drawn with North at the top, and he is facing South.

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Adam turns 30° anticlockwise.

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Now the Sun is slightly to his right, slightly West of South - this is early afternoon. Another 30° turn and the Sun is further to the West, and so late afternoon. He turns another 30° and the Sun is over his right shoulder, in the West. This is Sunset.

Adam turns another 30° anticlockwise.

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This is night-time - he cannot see any part of the Sun at all.

He makes some more 30° turns anticlockwise.

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The Sun rises in the East and then moves until it is back to the South and midday.

We say “The Sun rises in the East and sets in the West,” and one of the words that we usually translate into English as East actually means “in the direction of the rising Sun,” but in fact because of the tilt of the Earth the direction of sunrise varies from South East in the Winter to North East in the Summer, and similarly in the West for sunset. Sam uses his globe to show his friends why.

In English we often use the same word to mean two different things, for example “There are twenty four hours in a day, but the days are longer in the Summer than the Winter.” Twenty four hours is a solar day, the time it takes for the Eath to rotate on its axis, but we also use the word day to mean the time between sunrise and sunset, and the word night to mean the time between sunset and sunrise, but these are different at different times of the year. Usually it is quite clear which day we mean!

Sam has an App (LunaSolCal) for his iPad which gives the time of sunrise and sunset for where he lives for each day, and a lot more information about the Sun (and Moon), including the length of each day and the time of twilight. It does not give any information about the stars or planets, he has a separate App (Planets) which does that.

This App is not primarily designed for children, so it contains lots of information which he does not use and cannot understand, but Victoria asks him what twilight means and he tries to explain.

After Sunset it starts to get dark. Civil twilight is the time after sunset when motorists have to turn on their car lights, nautical twilight (for sailors) is the time when you cannot see the horizon (the boundary between sea and sky), and astronomical twilight is the time when the sky is totally dark (except for the Moon, stars and planets of course). The Golden Hour, just after sunrise and just before sunset, is the time when the Sun is quite low in the sky and the light is at its best for painting and taking photographs.

Many animals such as owls and badgers are nocturnal - they are most active at night. Other animals such as blackbirds and butterflies are diurnal - they are most active during the day. Man is by nature a diurnal animal, and until about three hundred years ago most people did not go very far from home after sunset. Watching the Sun set is a very definite ending, and so originally for thousands of years each day ended, and so of course the next day began, at sunset. Today for most people one day ends and the next one begins in the middle of the night, but some religions such as Islam and Judaism still use the old way - the Jewish Sabbath is on the day which most people call Saturday, but it actually begins at sunset on Friday.

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© Barry Gray last revised January 2020