Galaxies

Its really fascinating that once humans didn’t know what is beyond our galaxy. But a discovery by Edwin Powell Hubble changed everything.

The 100-inch telescope at Mount Wilson was the largest in the world in the early 1900s. At that time small patches of light in the sky were termed as Nebulae and were thought to be existing inside the Milky Way.

We know that when a star shows fluctuation in its brightness the reason may be a planet orbiting it. But there are some variable stars named Cepheid variables which show fluctuations in their brightness for some different reason. 

When the star is relatively cool it contracts thus its core contracts and it generates more heat and then star begins to expand. Energy is released before and after the expansion thus the star cools and contracts. The process repeats and that’s how we see fluctuation in its brightness.

Our pole star, Polaris is also a Cepheid Variable.

Edwin Hubble also discovered a Cepheid Variable in  a Nebula named Andromeda and thus using its fluctuations and luminosity he calculated its distance and thus the distance of Andromeda Nebula from Earth. It was 900,000 light years away. And American astronomer Harlow Shapley had determined that the Milky Way was only 100,000 light-year across. So it must be outside our galaxy. 

And later many stars were found in the nebula and thus it was proved to be a galaxy.

(Later it was proved that the distance measured by Edwin Hubble was not correct, please read this post.)

Picture of Andromeda by Edwin Hubble
Image credit: http://obs.carnegiescience.edu/PAST/m31var

Now we know that our galaxy is only a part of 100 billion other galaxies!

Image credit: http://hubblesite.org/newscenter/archive/releases/2012/37/image/a/

 More beautiful pictures can be found on Hubble website. 

Tessellations

Tessellations will appear everywhere if you have built a habit of seeing them. In shirts, dresses, on the bed-covers, curtains, buildings, flowers, etc.

But mostly in nature we do not see tessellations but symmetry. So how tessellations and symmetry are related?

I remember butterfly wings which are symmetrical, and tiles in my home which repeat (or tessellate). 

The building block or tile used in tessellations is repeated over and over again to fill the whole space.

For example here are few tessellations with similar tiles:

Sometimes the shape used is similar but the way it is arranged or its colour is different. And that’s how different tessellations can be made using similar shapes. The detailed description can be found here: Tessellation symmetry

Triangles, squares and hexagons are the only shape which can tessellate regularly. And others can be made to tessellate for example by using two different shapes.

The work of Maurits Cornelis Escher is very famous in the world of art and mathematics.

M.C.Escher
Image source: http://www.mcescher.com/gallery/italian-period/hand-with-reflecting-sphere/

As written on the website of Tessellations:

During his life, he became obsessed with filling surfaces with pictures that did not overlap or leave spaces. Aged 68, he stated, “Filling two-dimensional planes has become a real mania to which I have become addicted and from which I sometimes find it hard to tear myself away.”

First Tessellation of M.C.Escher
Image source: http://www.tessellations.org/tess-escher6.shtml

He also made tessellation which grew smaller on the outside, and similarly in reverse.

Image source:  http://tessellations.org/eschergallery24.shtml

So let’s keep on seeing patterns in nature! Happy World Tessellation Day.