Why do we See what we See?

The western highlands of Scotland, bathed in the visible light of our home star.

When we think about the vast array of electromagnetic radiation all around us – from Gamma rays, X-rays , UV, Microwaves and Radio waves – a natural question to ask is why do human eyes see in a very narrow band we call ‘visible light’?

The answer is undoubtably tied to the energy output of our nearest star – the Sun. Its peak radiation just happens to be at this ‘visible’ band of radiation. I’ve illustrated this below with a black body radiation profile of our Sun.

Our eyes have therefore evolved to ‘see’ this particular narrow range of otherwise insignificant wavelengths. There’s nothing inherently important about visible light – in fact it makes up a tiny 0.0035 percent of the entire electromagnetic spectrum!

Understanding this makes me wonder about the potential sensory apparatus of life that might have evolved elsewhere in the universe. Other stars with different stellar classifications to our Sun have markedly different peak radiation profiles.

If we had evolved next to a source of intense gamma rays for instance, we would very likely be completely blind to visible light but adept at observing small granular differences in the intensity of gamma radiation.

The Final Evolution of our Sun – illustrated by Adolf Shaller

I wanted to share some images with you that had me transfixed when I was a young boy (and still do to this day). I recall first seeing them in a hardback book of my father’s called Cosmos (which presumably accompanied the TV series that was being broadcast at the time).

The images depict the fate of our planet as the Sun transitions into a red giant star, at the very end of its life, some 4-5 billion years from now.

As the temperature of the Sun slowly increases, the oceans recede and our precious atmosphere is stripped away. Eventually the whole horizon is overwhelmed by the Sun in a bloated distended form, with the final image showing the Earth completely barren and parched.

I remember wondering at the time – where would all the people and animals be? Would we perish or find some new star to call our home? I think it was the first moment I glimpsed the immensity of stellar time scales and how tiny human lives and endeavours appeared to be next to these vast physical processes.

This is still what fascinates me most about astronomy and cosmology, and it’s amazing how something as natural and simple as looking up at the stars is a gateway into these incredible realms of the imagination.

Anyway here are the images, including their original captions. I was also pleased to find out that Adolf Shaller is still producing amazing art. Try an image search on Google with his name and enjoy.

‘The last perfect day’
‘The waters recede and most life is extinguished as the sun starts to swell and its luminosity rises.’
‘The oceans have evaporated and the atmosphere has escaped into space’
‘The sun, now a red giant, fills the sky over a dead planet. As we see in the next section, the red giant will eventually throw off its outer layers and become a white dwarf.’

‘Not too hot and not too cold’

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The Goldilocks zone around three different type of stars

The Goldilocks Zone.  The above image is a great illustration of the relative size of the habitable zone around different types of star, with stars like our Sun at the bottom.

Even very dim M class dwarf stars (pictured top) could harbour planets with liquid water – the planets would just need to be situated much closer in. These stars can have very active magnetic fields however, frequently throwing harmful radiation out towards any orbiting planets.  M class stars are also extremely stable, some destined to burn for over 100 billions years, much longer than our Sun which has around 4 billion years of fuel left.

In the middle we see the K class dwarf stars. These will also out live our Sun (by a factor of 4), have nice wide zones of habitation, and much less magnetic activity than the M class stars.  Potentially these K class stars are the ideal incubators for the slow evolution of life, and there’s plenty of them. Nearly 13% of stars in our galaxy are K class red dwarfs.  That’s approximately 26 billion in our galaxy alone! 

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An artist’s impression of a rocky world orbiting a red dwarf star, like the M and K class stars mentioned above.

Solstice Sunsets

Video from the shores of Bunchrew looking over Ben Wyvis, panning from the north west to north east

The sunsets in the Highlands of Scotland are some of the best in the world when conditions are right, especially around the solstice when the setting Sun grazes just 8 degree below the northern horizon producing mesmerising night long sky glow.

On June 22nd I camped out at the Bunchrew shoreline with my daughter Violet and managed to capture some video and still images of the sunset looking north towards Ben Wyvis.  Footage captured around 10.45pm.

 

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Venus Morning Star

The planet Venus is a brilliant morning star at the moment. Catch it rising in the south east ahead of the Sun between 5.30am and 7.30am.

With keen eyesight and binoculars you should be able to discern Venus’s phase, currently a beautiful crescent. A telescope will make this much clearer as demonstrated by this video footage I shot last year, when Venus was ‘the evening star’.

Over the month of November Venus will get brighter as its phase waxes from a thin crescent to a 25% illuminated disc at month end.  Despite this brightening Venus is actually travelling away from us and after December 2nd its brightness will begin to diminish as it pulls further away from earth and its disc size shrinks .

Once Venus passes behind the Sun it will eventually reappear as an evening star around mid August 2019.

Clear skies!

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