…is not gold. From the Merchant of Venice, William Shakespeare gave us a vision that Led Zeppelin later crafted into song. Not all that glitters is gold, but what makes gold special?
Part of gold’s appeal is its longevity; it stays brilliant seemingly forever. Gold does not tarnish. Gold sits in the periodic table of elements between platinum and mercury, neither of which tarnish. But platinum looks like silver, mercury too, and try to make a ring from mercury! Tarnish is a kinder term for rust, resulting from oxygen’s greed for electrons. Many metals have an electron or two to share and oxygen from the air snaps them up, the reaction forming a surface oxide on the metal, of that metal. Rust for iron, tarnish for silver. Copper, bronze, and brass get a patina. Gold simply does not have an electron to spare, therefore, no oxidation. It stays shiny for years, decades, eons.
Why does gold look, well, gold? Its atomic arrangement favors electron relativistic quantum effects with light. In other words, due to the electron’s speed relative to light it tends to absorb short wavelength light…blues. The light reflected from gold then is predominantly longer wavelength light…yellow and orange. That’s why it looks golden.
Oh, yes, gold is also pretty rare. That helps with its popularity. Where does gold come from and why is it rare?
Gold comes from stardust, but not just any stardust. The current generation of stars contain a small percentage of gold and that gold came from first generation stars that mostly went supernova. Even our Sun, which will not go supernova or even nova has some of that gold. Our universe is littered with neutron stars and black holes, the remnants of massive stars that went supernova. It takes a supernova to make elements heavier than iron.
Inside a massive star’s core, hydrogen fuses into helium, then helium into carbon…cascading until iron is produced by fusion. Iron fusion is not sustainable, and the star’s core collapses as fusion peters out. Gravity takes over but hits a wall when neutrons become packed. If the core is massive enough gravity wins and boom-woosh, a black hole. If the core is not massive enough gravity loses and boom, a neutron star. In both cases a supernova occurs and within the extreme pressures and heat we get heavy elements…including gold. Supernovae are and have been spewing heavy elements throughout the universe.
Why is gold so rare on Earth? Well, it might not be. It’s just rare in Earth’s crust. In theory a couple of thousand miles down there is quite a cache. How to get it?
What’s in the Sky?
October 12-15; 1 hour before sunrise; east: A waning crescent Moon moves past brilliant Venus.
Comet 88P/Howell: Sets in the southwest about an hour after dusk. It is in Ophiuchus, and just south of the pipe nebula on October 12. Use a 4” or larger instrument.