Mr Bennett’s Facts Issue #1 – The Earliest Sunset

Hello everybody,

Mr Bennett here. As you know I run this website for the school. As you may not know I am also obsessed with facts.

So I have decided to start an occasional series on the website where I share interesting things for the children reading this to explain to their parents and carers, as Mums, Dads and carers are clearly not as good at learning things as kids….

So here is Issue #1 – The Earliest Sunset#

Ask your adult when the shortest day of the year is WITHOUT LOOKING (grown ups cheat, don’t let them).

Did they say something like 21st or 22nd of December? Good. They know that. If they didn’t you have a bonus fact to teach them.

That is the day of the year where the sun is in the sky for the least amount of time, and this year it is the 22nd of December.

Now spring our trap. Ask them when the earliest sunset is, the day when the sun sets at its earliest time in the afternoon. I reckon they’ll say – “The same day”.

THAT IS WRONG!

The earliest sunset is actually today! December 15th.You can also ask them when they think the latest sunrise is, the latest time in the morning that the sun rises. They’ll be confused now but they probably won’t guess it’s December 29th.

You see what we have here is a MGUDKT Situation AKA a “Most Grown-Ups Don’t Know This” Situation.

So what is going on? Why do these three things not occur on the same day?

It’s all to do with how the path the earth takes as it moves around the Sun.

Here’s the simple model that most people carry in their heads as explained by the BBC.

But this has been simplified. The Earth doesn’t move in a circle.

If the Earth moved in a circle all three of these events would take place on the same day, but it doesn’t. The Earth moves in an oval shaped orbit called an ellipse.

So the weird thing is the length of a day is constantly changing all year.

Now you may say “stop Mr Bennett. That’s just silly, every day is 24 hours, look at the clock”, but that is just our ‘chop up the year into days hours and minutes human idea’ of a day. A rough estimate.

Real days are the actual time it takes the earth to rotate and real (aka solar) days are much more like people themselves than people’s idea of a day. They vary a lot as the path changes because as well as spinning on its axis the Earth is turning on a path in space.

When it is at the extreme and pointier ends of the ellipse (Spring and Autumn) days are shorter as Earth is putting the brakes on its path and turning hard. You may also notice the length of the sunlight changes a lot around these times we call equinoxes. When it is on the smoother part of its path (summer and winter) the days are longer and you may notice the change in sunlight length is slower (these are called solstices).

Also there are other complications because the earth’s speed is also changing due to a constant gravity fight with the Sun.

What this means though is that when combined with the tilt of the earth there is an unevenness to day length and so an unevenness to sunlight length and the speed it changes at.

All this means that there is a difference between when the earliest sunset is and the latest sunrise as the centre of the solar day wobbles in relation to our clock time.

If you didn’t understand that don’t worry. The important thing is your grown up didn’t either. Due to reading this you owned a grown up.

Check back next time for more facts.

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