Orphan blocks, also called stale blocks, are blocks that are not accepted into the blockchain network due to a time delay in broadcasting the block to the network of miners. Orphan blocks are normally valid and verified blocks but have not been accepted and added into the rest of the blocks in the blockchain.

An orphan block is valid since its outcome after a proof of work mechanism is correct. But it isn’t accepted by a large number of miners into the rest of the blockchain. They are stored in a pool of orphaned blocks. Hence, all the information it contains becomes meaningless to the blockchain and the entire network.

Orphan blocks occur frequently and mostly by chance. An average of 1 to 3 of all the blocks generated in the Bitcoin network in a day are orphans. Miners who have successfully generated blocks that become orphan blocks will not receive the mining reward.

What Is an Uncle Block?

In a similar process to how Bitcoin creates orphan blocks, uncle blocks are created when more than one child block is created from a parent block in the Ethereum blockchain. Uncle blocks are bound to be created many times because all the nodes that maintain the ledger are not updated immediately when a new block is mined.

When two blocks are mined simultaneously, only one gets validated across nodes on the ledger. The one that is left unconfirmed becomes an uncle block.

Uncle blocks are commonly related to the Ethereum protocol. Even if uncle blocks are similar to orphan blocks, some slight differences exist between the two. While miners of an orphan block are not rewarded for producing them, miners are rewarded for producing an uncle block. For a valid block successfully mined on the Ethereum network, a miner is rewarded with a block reward of 3 Ether. Contrarily, a miner of an uncle block earns a reward of 2.625 Ether.