Our debt to starlight

Everything we have ever seen, we have seen by starlight.

During the day, our surroundings are lit by the sun, a yellow dwarf star. On a clear night, we can see by starlight.

If the moon is in the sky, that moonlight is reflected sunlight. The light from our campfires or camping lamps come from burning plant materials that contain energy from sunlight. Our electricity also comes from sunlight.

Hydroelectric power comes from the work the sun does in evaporating seawater so that it falls on high ground as rain.

Wind power comes from the effects of solar heat on the atmosphere. Coal and oil are sunlight captured millions of years ago.

Nuclear power comes from elements like uranium, which are forged in exploding stars. There are very few exceptions, for example, tidal power.

We see those great gas and dust clouds in space because stars illuminate them. The planets and other objects in our solar system are visible because they reflect sunlight.

Without stars, our universe would be dark, cold and lit only by the fading infrared afterglow of the Big Bang.

The elements needed to make us, our planet and all the other bodies in space come from stars. About 380,000 years after the Big Bang, the universe consisted of hydrogen and some helium.

The first stars formed from that hydrogen. They obtained energy by converting that hydrogen into other elements: atoms with masses up to that of iron.

Many of those first stars were blue giants, which shone very brightly, exhausted their fuel quickly, collapsed and blew up. In the explosion all the heavier elements, such as copper, gold, silver and uranium were formed.

All these by-products of energy production were ejected into space and mixed with the hydrogen in the clouds. After a few generations of stars the clouds contained all the elements needed to form planets, all the other bodies we see in the cosmos, and of course us.

The story does not end there.

Stars don't only supply the light and heat needed by living things, they also played a part in producing the raw materials. Over millions of years, the elements in those enriched clouds started to react, forming a huge assortment of chemicals.

These reactions were helped along by ultraviolet light from nearby stars. In open space, the ultraviolet is so fierce that no complex molecules can form, and any existing ones will rapidly be destroyed, just as solar ultraviolet rays break down molecules in our skin.

However, inside the clouds, the ultraviolet is much weaker and provides energy to drive chemical reactions.

We have managed to duplicate some of these reactions in the laboratory. The resulting witches' brew of complex organic molecules included amino acids, the building blocks of proteins.

When new planets form, they inherit a lot of cloud chemicals. It seems that most planets start off with the chemicals forming the basis for life.

However, in most cases the conditions are not suitable for life to develop. Even when conditions are right, as yet we have no idea what happened to get from amino acids to proteins.

\Our ideas include chemical reactions in the sea, or in tidal shallows or muddy swamps. However, at the moment, they are little more than suggestions.

When small stars like the sun reach old age, they start to lose material, in a sort of highly enhanced solar wind.

More massive stars end their lives in a spectacular fashion, by exploding. In these explosions, or supernovae, shock waves and clouds of ejected high-speed material fly off into space, impacting nearby gas and dust clouds, which then collapse and form new generations of stars.

It is interesting that if some of the numbers describing the basis of matter were even slightly different, there would be no stars, and the universe would be dark, cold and lifeless, and astronomically not very interesting at all.

• Jupiter, shining like a searchlight, or an aircraft landing light, rises around 10 p.m.
• Saturn rises at 11 p.m.
• The moon will be full on the 17th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.