Questions

Sunspots are a magnetic phenomenon on the Sun.

The reason a sunspot appears dark is that they are cooler than the rest of the Sun's surface and also the gas inside the spot where the magnetic field is strongest is only emitting about 1/4 as much light as from the rest of the solar surface. 

A software developer called Satoshi Nakamoto proposed bitcoin, which was an electronic payment system based on mathematical proof. The idea was to produce a currency independent of any central authority, transferable electronically, more or less instantly, with very low transaction fees. Bitcoin’s most important characteristic, and the thing that makes it different to conventional money, is that it is decentralized. Bitcoin is created digitally, by a community of people that anyone canjoin. Bitcoins are ‘mined’, using computing power in a distributed network.This network also processes transactions made with the virtual currency, effectively making bitcoin its own payment network.The bitcoin protocol –the rules that make bitcoin work –say that only 21 million bitcoins can ever be created by miners. However, these coins can be divided into smaller parts (the smallest divisible amount is one hundred millionth of a bitcoin and is called a ‘Satoshi’, after the founder of bitcoin). Bitcoin stores details of every single transaction that ever happened in the network in a huge version of a general ledger, called the blockchain.

Precedent means prior arrangement; no other option is suitable. Opportunity means a favorable juncture of circumstances. Chance is a synonym for opportunity, it also means something that happens without intension. possibility is the condition of being possible.