## Saturday, 2 May 2015

### Exploring the Cosmos: Powers of Ten, Historical

The Universe is vast and it is almost impossible to describe how big it is.
A good way to get some feel for the size of the Universe is to use the Powers of Ten method.
The idea is by looking at the objects in a square of side 1 meter. Then increase the area of observation to a square of 10 meters and see what objects are present.
In each successive step increase the side by a fact of ten and in 25 steps, one is looking at an area of side 10^25 by 10^25 meters - which contains most of the observable Universe.
One can also reduce the size of the side of the square by successive factors of 10 and look at the microscopic world.

This is most beautifully done on the website I do hope that you will enjoy spending some time on this website - I recommend it highly.

In the following I shall publish the slides for my first talk on Exploring the Cosmos.  (Click on the slide to view its bigger image)
The first real advance in understanding the Solar system and the stars came from Aristotle (384 BC - 322 BC)
Retrograde Motion of planets:  Planets did not move in smooth circular path but looped their paths sometimes. this would be against the perfection that Aristotle's model demanded.
To explain retrograde motion, Ptolemy devised a complicated structure of perfect spheres...
Aristotle-Ptolemy Universe held sway, with the backing from the Church for almost 2000 years. Anybody who spoke against it was severely punished.
Shorthand way of writing powers of ten.  This allows big numbers to be expressed in compact form.
Distances are so large that they are measured in terms of the distance travelled by light in a certain time.  A light year does not measure time but the distance that light covers in one year.  A light minute is the distance that light travels in one minute.
Just a picture of the constellation - stars we can see in the Northern sky
Universe has a wide variety of objects that we shall talk about in this course:
Sizes of stars vary tremendously.  The figure compares some of these: