Thursday, 13 August 2020

Astrognome 100 Great Stars Introduction

 Astrognome 100 Great Stars Introduction

Following on from the Astrognome A-Z of constellations I intend to present the Astrognome 100 Great Stars. Many people I am sure could suggest an alternative 100 stars but hey this is my selection. I have tried to stick with the brighter and better known stars.

I thought it would be useful to present a very short introduction to the stars.

Look into the night sky there appear to be millions of stars, however on any clear night from anywhere really dark site away from city lights it is possible to see around 3,000 stars without a pair of binoculars or telescopes. The stars appear to be randomly spread across the sky.

The stars are actually grouped into patterns or constellations these tell stories from ancient Greece. However although the star stories are Greek most of the star names we use today are Arabic.

There are 88 constellations in the sky, 48 date back to the times of ancient Greece while the other 40 constellations were added in more modern times, by modern I mean the 15th and 16th centuries. Most of the modern ones are in the southern hemisphere and were added when European explorers went there, while some were added in the northern hemisphere to fill gaps between the classical constellations.

If you look at a star map or an app on your phone or use a tablet you will see the stars have strange looking symbols besides them. These are letters from the Greek alphabet. In 1603 Johann Bayer allocated the 24 brightest stars of each constellation a Greek letter. In theory the brightest star is alpha followed by beta, gamma etc until omega. However we will discover that this system does not always work.

The brightness of a star is measure by its magnitude with the brightest stars having minus numbers and the larger the magnitude number the fainter the stars. Assuming you are in a very dark site and have good eyesight we can see stars to magnitude 6 with our eyes without using binoculars and telescopes. You will notice that some stars are much brighter than others this can be because they are fairly close to us, or because they are genuinely very bright stars. However appearances can be deceptive because some stars only appear faint because they are a very long way away.

Astronomers use the speed of light to measure the distance to the stars, although we use the mile to measure distances on Earth it is too small a unit in space. Astronomers use the speed of light to measure the distances to the stars. Light travels at a speed of 186,000 miles per second or 300,000 km per second. In one year a particle of light will travel around 6 million million miles that is a 6 followed by 12 zeroes. Stars can be 10s, 100s 1,000s or even millions of light years away!

When you look at the stars it is possible to see that they are different colours and rather surprisingly blue stars are hotter than red stars. I know we say that things are red hot, meaning that's very hot, but if you look at a flame around the edge it will appear reddish while in the middle it is blue. This is the hottest part of the flame. And although stars don’t burn like fire they produce their energy through atomic reactions the colour principle is the same. Therefore when you look at a blue star it is much hotter than a red star. Astronomers divide the stars into different classes by using a series of letters with O class stars the hottest and M class stars the coolest.

Stars do come in different sizes giants and dwarfs and although our the Sun is very big by our standards, it is about 900,000 miles across some stars are much bigger.

That’s it for this very brief introduction to the stars, I hope you found this short section helpful.

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