Wednesday, 29 June 2011

Has it gone over your head!

Ever sat outside on a nice clear, warm, moonlit evening with the sounds of the countryside all around you. The soft chirp, chirp, chirp of a Cricket or the odd hoot of an Owl. When combined with a glass of wine, good conversation and lively company. This is the idyllic sort of situation that we would all enjoy.

Yet it is also possible to enjoy any clear, moonless, evening even in the depth of winter by observing the night sky. As boaters we get the chance to moor up away from the bright lights of the towns and cities. Its only then that you get the chance to appreciate and enjoy the real wonder of the night sky.

My introduction to the night sky came as a child, with my mother naming and describing the stars she had been taught about when she was a child. That lit a fire in my imagination that smoldered for many years. Occasionally fed with the late night "Sky at Night" presentations of Patrick Moore. I had my own simple equipment, I much preferred to use binoculars rather than a telescope.  My interest turned from a hobby into an obsession. Many years later in a galaxy far far away,  I used to teach astronomy for a while. We had a good set-up with a purpose built observatory and a very good Meade telescope.

Yet, you don't need a purpose built observatory. You don't  even need to use a telescope. It is surprising what can be observed with just the naked eye. The interesting thing is that when you are observing the night sky, you also become much more aware of other things that are happening around you.

The tools needed are a moonless night, a folding deckchair, a sleeping bag and a pair of low power binoculars are optional. Set the deckchair to its lowest point, so it feels like you are almost in bed. What we are going to observe is going to be overhead. setting the deckchair low will save on any neck discomfort from craning your head back.

It can take quite a while for your eyes to fully acclimatise to the dark, but when they do, its surprising what we can actually make out of our surroundings. Our peripheral vision is usually the more sensitive to low light conditions. So when observing an object, look slightly to one side for best effect.

Position the deckchair so that you are looking towards the South. Put any other items that you might need close at hand. Make yourself a small red light torch (cover over the lens with something a deep red colour, like a sweet wrapper for instance. (the red coloured sweet wrapper contents should be eaten first) I think that Quality Street make for good coloured cellophane wrappers. The red light can be used to illuminate our surroundings if need be without spoiling our night vision. A thermos flask of hot coffee for the very cold nights in winter helps. Climb into the sleeping bag and then settle back in the deckchair and let your eyes begin to adapt to the low light conditions.

As your eyes become more accustomed to the dark, so do your ears, and you will become aware of  the even the faintest of sounds. First there are the obvious sounds of the local wildlife. More intriguing at times are the mystery noises that you have never noticed before. All the sounds have natural origins, the difficulty comes from deciding what the origins actually are.

It is surprising what will come close when you are sat quiet and still. My best so far is a Stoat that was out foraging. It even ran over my feet.

I usually spend up to half an hour just listening with my eyes shut. I have sometimes managed to fall asleep during this! This is when an MP3 player comes in handy, with some good rousing music to help keep you awake. Try not to sing along, I have forgotten myself and done that as well!

So what can we look out for.

We are all aware of the stars and the constellations, or are we?

It is good to be able to pick out some of the more prominent constellations. Typical of this is the constellation of Orion. The best time to view Orion is during the winter months.

Remember that you need a good imagination to visualise what the stars are intended to represent.

Orion, often referred to as "The Hunter" is the most prominent and easy to identify constellation visible in the night sky. The name refers to Orion, a hunter in Greek mythology.

Remember the nursery rhyme. "Twinkle, twinkle, little star, How I wonder what you are. Up above the world so high, Like a diamond in the sky." We have all taken the time to teach that to our children, in the same way it that it was taught to us by our parents. Its only later that we learn that the stars in the night sky are not diamonds, just small pinpricks of white light.

Here comes the first surprise, not all stars are white. Some are blue and some are red, its just that we don't notice the colour until we take the time to look. There are several interesting coloured stars in Orion that can be be observed with the naked eye.

Rigel the star in the left leg of Orion is a young blue-white star. One of the most luminous of all stars. It has been estimated that Rigel's luminosity is something like 36,000 times that of the sun. 

Betelgeuse the star in Orion's right shoulder is not shining with a steady light.  It is a red star, expanding and contracting spasmodically, but so irregular that no one can predict exactly when it will expand or contract.

The main stars that make up the Orion constellation are :-
Rigel Orion's left leg.
Betelgeuse Orion's right shoulder.
Bellatrix Orion's left shoulder.
Mintaka, Alnilam and Alnitak Orion's belt.
Saiph Orion's right leg.

What we are observing is not what is happening now in the constellation of Orion, but what was happening a long way back in time. The light from Rigel set off towards Earth when Henry III was on the throne. Light from Betelgeuse set off when Henry the VII was on the throne.

One of the hardest things to comprehend is the vast distances that the objects are from us on planet Earth. Measuring the distances in miles or kilometers would give such vast numbers. So we use the speed of light to measure distance.  Light travels at 186,000 miles per second or 300,000,000 metres a second in new money.

Light from the Sun reflected from the Moon takes just under one second to reach the Earth. Light from our own star, the Sun (93,000,000 miles) in about 8 minutes and 19 seconds. The next nearest star to Earth is Proxima Centauri at approximately 4.2 light years away. Rigel is 773 light-years away. Betelgeuse is 522 light-years away Bellatrix is 243 light years away. Mintaka is 900 light years away. Alnilam is 1359 light years away. Alnitak is 800 light years away Saiph is 724 light years away.

In our own galaxy the Milky Way, light takes about 28,000 years to reach Earth from the galactic centre. For light to travel from one side to the other of the Milky Way is about 100,000 years. Our nearest galaxy neighbour is the Andromeda galaxy, light takes about 2,500,000 years to reach Earth.

There are billions of other galaxies out there.

I must dig out my copy of the Hitchhikers Guide to the galaxy and my Red Dwarf videos.


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