Questions About Earth Axis

I have thought recently that the quality of bright day light appeared to be different to how I have always perceived it, but I dismissed it. However I’ve noticed that at midday shadows were very long, at that time shouldn’t they be almost zero or tiny; I then realised that the Sun wasn’t overhead but at a lower declination that I thought it should be – ie not over head. I then thought how much cooler it had been this year, and that if what I was seeing was correct that the Earth would have tilted, and in a way that meant we (the UK) were further North. I’ve tried to disabuse myself of this this rather worrying view, but having looked on the net & Youtube, it’s not just me that seems to be noticing this!!! It can’t be so, can it, wouldn’t it have been on the news, or at least ‘The Sky at Night’; What am I seeing???

You have made some excellent observations!  Indeed, in the U.K., the sun has not been directly overhead this summer.  Nor has it been directly overhead, in summer or winter, in previous years.

The reason for this is the tilt of the Earth’s axis.  Only places between latitudes 23.5 degrees North (the Tropic of Cancer) and 23.5 degrees South (the Tropic of Capricorn) will ever have the sun directly overhead.  The sun will be directly overhead for all locations on the Tropic of Cancer on the summer solstice at noon, and the sun will be directly overhead for all locations on the Tropic of Capricorn on the winter solstice* at noon.  Here is a picture illustrating the summer solstice.

A wise Greek named Eratosthenes used this fact to measure the circumference of the Earth.  He lived in a city called Alexandria, which was north of the Tropic of Cancer.  He knew that on the summer solstice, a city a bit further south called Syene had the sun directly overhead because the sunlight shone directly down a well.  In Alexandria, he placed a stick vertically into the Earth, and on the summer solstice at noon, he measured its shadow.  He used the length of the shadow and the length of the stick to calculate the angle of the sun (83 degrees above the horizon, or 7 degrees away from passing directly overhead, since there are 90 degrees in a right angle).  Here is a picture that shows the setup of his experiment.

Because the sun is very far away from the Earth, its light rays that reach the Earth can be considered parallel.  As shown in the diagram, the difference in angles of the shadows in Alexandria (7 degrees) and Syene (0 degrees) was the same angle as the angle of separation between the two cities, as measured from the center of the Earth.  Thus, if he knew the distance between Syene and Alexandria, Eratosthenes could measure the distance around the Earth by relating the the angle between the cities (7 degrees) to the number of degrees in a circle (360).

Eratosthenes estimated the average speed of a camel to calculate the distance between Syene and Alexandria as 5000 stadia, giving the Earth a circumference of 360/7 * 5000 stadia = 252,000 stadia.  The ancient unit of the stadion varied, and it is not clear which version Eratosthenes used.  Thus, his measurement corresponds to a circumference between 39,690 km and 46,620 km.  Considering that the Earth has a circumference of 40,008 km around the poles, Eratosthenes’ measurement was within 16% of the true value.  That’s pretty good considering he had to estimate the average speed of a camel!

The U.K. is north of the Tropic of Cancer (London is about 52 degrees North), so the sun will never be overhead.  However, you can repeat Eratosthenes’ experiment if you would like (and if the weather cooperates). Wait until one of the solstices or equinoxes (first day of spring/summer/autumn/winter) and put a pole vertically into the ground.  At local noon**, measure the length of the pole that sticks out of the ground and its shadow.  Find the angle between the sun’s rays and the pole by calculating arctan(length of shadow/length of pole).  You know that the sun is overhead at one of the following locations: Tropic of Cancer (summer solstice), equator (autumnal or vernal equinox), Tropic of Capricorn (winter solstice).  The angle you have measured is also the angle of separation between you and the location where the sun is overhead.  Look up the distance between yourself and that location, in kilometers.  Do (360/your angle) * (distance to that location) = circumference of the Earth.  Were you close?  You can also use the angle you measured to find your latitude: your angle + latitude of comparison location (23.5, 0 or -23.5) = your latitude.

As for the weather aspect of your question, weather cycles are complicated!  The weather can vary a lot from year to year.  I suggest looking at yearly averages *and* records, which will convince you that this year was not really that out of the ordinary.  

Various aspects of the Earth’s orbit do change, but on timescales of thousands or millions of years, which is much longer than a human lifetime!  

As for youtube, do not trust the internet!  Anyone can post whatever they want to say on youtube.  They do not need to be qualified or an expert.  By asking an astronomer, you did the right thing to get a scientific answer to your questions!

I hope this helped.

*The solstices are defined by the seasons in the Northern hemisphere.
** Local noon is when the sun is highest in the sky, and this is not necessarily 12:00pm on your watch!  You should look this up for your precise location on the date that you do the experiment.