As previously discussed in the Tip of the Night for May 27, 2017, blockchains are a series of hash values stored on distributed databases and used to prevent the use of a digital token like a bitcoin more than once. In addition to the hash values there are also time stamps and transaction data that are part of the blockchain. Blockchains are recorded in publicly distributed ledgers. But where are these publicly distributed ledgers?
There is no central authority that records the blockchain transactions. As a digital currency, the bitcoin exists on the ledger itself - the ledger doesn't merely record the transfer of a currency. The blockchain ledger can be accessed on multiple sites. For example, this blockchain ledger available on Block Explorer:
. . . is the same as this ledger available on blockchain.info:
Note that the time and byte size are the same, as well as the hash values.
About 6-10 times an hour a block is published which lists verified transactions - which bitcoins have been spent.