# Eclipse, bus ride and theory of relativity

Hi guys!
It is two days since eclipse of sun.
First of all I will just remind you what eclipse is.
So, it is shadow of moon, because of its rare position between sun and you.
Imagine having lamp. It is your sun. Take your hand (moon) and move it between you and lamp. That is how eclipse works.

There few kinds of it. There is full eclipse.
This one on the left is full eclipse from year of 1999. Picture was taken in France. For full eclipse you usually need to go to some specific place which is calculated by some math quys 😀 . Because that is the only position you can change… you can not change position of sun, moon or earth but you can travel yourself.

Here on left is picture of solar eclipse. You can see that shadow of moon is not visible everywhere… only on very small spot (about 250km^2) is full shadow.
There are lots of things that have to work together if you want for example to have full solar eclipse visible from window of your house.
Because moon is 400x smaller than Sun, Sun has to be 400x further away. At same point your house has to point exactly towards sun and at the same moment moon at right distance has to orbit across your point of view when you are looking at sun.
Well that wont happen 😀 .

Because moon is slowly going away from earth and sun is gaining volume, last full solar eclipse we will be able to see will be 600,000,000 years from now.
You can see list of eclipses on wikipedia. Next total one will be March 9 2016. But it will be somewhere in pacific ocean.

Anyway, two days ago I was in bus by the time when eclipse was seenable. Luckily i was sitting in back seat from which you can see huge part of sky. Well I forgot to take some kind of black glass so I saw it for few seconds before I was too blinded, hope nothing happened to my eyes. Anyway I am looking forward to next eclipse and I hope that you guys did see it!

Eclipse was very important when Einstein wanted proof for theory of relativity. He was predicting that as huge objects bend spacetime, light will be curved if between sun and you is some object with huge gravitional field. Actually moon has too weak gravity so you cannot really see it but when you have quasar and black hole is between quasar and you, you can see that effect of bended spacetime. It is called effect of gravitational lens. http://en.wikipedia.org/wiki/Gravitational_lens On wikipedia page you can see short video of how it looks like, it is pretty amazing.

Dragallur

# 2) Four fundamental forces: Gravitation

Gravity or gravitation is one of four fundamental forces in the universe. It is also the weakest one as I said in the last post. Unlike other forces it works on much bigger distances. And it only pushes things together.
Imagine having a planet like Earth. It has poles. South pole and north pole. We can see that Earth gravity is pretty strong, it holds us here. So if electromagnetic force is 10^40(something like that) stronger, shouldn´t be electromagnetic field of earth insanely strong? No because electromagnetism works with +(plus) and -(minus) and they will cancel out (almost). Strong and weak interaction are working only on short distances so when you are forming galaxy or star you will work only with gravity.

There are two ways of imagining gravity. (Actually there are more but those are basic)
1) Newton´s way
It says something like this: Every particle in universe attracts all other particles in universe by force which is higher when mass of particles is bigger and is lower when particles are far away each other. Its equation is F=G*(m1*m2)/r
F is force of gravity
G is gravity constant (you can find it on wikipedia)
m1,m2 are masses of your objects
r is distance of objects
2)Einstein´s way

Spacetime is bended by all particles with mass. And it works with all particles even those which are massless, like photons.
Newton´s way does not actually explain some things like orbital of Mars (so it is kind of broken).
On the left is picture of spacetime. You can also imagine your bed which is probably very soft and when you push your matress it goes down. At that point your fist is actually kind of planet, star or black hole and it atracts other stuff around. If you take a ball lay it next to your hand it will go down to center of that hole you created.
I have found awesome video on gravity so here is link: https://www.youtube.com/watch?v=MTY1Kje0yLg
You will see that all forces have some force carrier. Gravitational carrier is massless particle called graviton. It is theoretical, which means it was not detected. Scientists even think that it cannot be detected, but we can see what it does: Gravity!