Nelson's Monument was erected in honour of Nelson, but also had an important real world purpose. It was erected where it is to direct vessels into Portsmouth harbour along a safe passage. It is still used now by the Navy to double check their high tech apparatus are all functioning correctly. The mouth to Portsmouth Harbour is about 5 miles away, and safe passage into the harbour was vital for all vessels.
The monument was planned by Nelson to celebrate the perpetual victories of the British Navy. The first fund for the monument was collected but never seen again, and letters were written to The Times, asking where this money had gone. It was not recovered. However the monument was eventually built after Nelson's death at the price of two days pay from the entire British Navy plus money from the Navy itself.
A bust of Nelson is atop of this column.
For this EarthCache we are going to explore the Curvature of the Earth. Historically the distance of the visible horizon at sea has been extremely important as it was the maximum range of communication.
You will need to work in either metres and kilometres, or feet and miles. Or you could do both if you wish.
Curvature of the Earth
The curvature of the Earth determines how far an item can theorhetically be seen. We are going to emit factors that effect the actual true horizon like weather and obstructions. The Earth is roughly a sphere, and it is possible to theorhetically see an item which is high enough from half of the globe.
We are also going to use basic calculations, for an estimate to the distance. There are many slight variations in these calculations online. This is for an approximate geometrical estimate only.
For metres and kilometres, where the Earth is 6371km radius
where d is km, and h is the height above ground or sea level in metres.
For feet and miles
where d is miles and h is height in feet.
And as this is also related to the sea, you may be interested to work out this in nautical miles,
where d is nautical miles and h is height in feet.
For this EarthCache you are required to do the following...
1. Go to the above coords and find out your elevation from sea level. You may need some sort of device or app to work this out for you.
2. Find out the height of the monument. This can be found at the above coords. You will need to work in the same units of measurement as you did for Q1
3. Add the two units to give you a value for your h
Work out the distance that the monument can be seen from one, two or all three of the above equations.
4. Given that the Entrance to Portsmouth Harbour is approx 5 miles, 8km or 4.5 nautical miles away, and the Eastern tip of the IOW is 12.5 miles, 20km or 11 nautical miles away. Can you explain whether the furthest point of sight would be nearer or further than these two, or somewhere in between.
5. You may like to play with calculations, and explore more heights, but why do you think that if you double the height calculated, the distance of sight does not double? What shape do you think the world need to be for the height and sight to increase at the same ratio? (There is a little bold clue above)
6. Email me the answers you have found from step 3 and 4 and your thoughts on Q5, and then please log your visit.
