About block 639
Bitcoin block 639 was mined by Unknown on January 15, 2009 at 11:31 PM UTC, 13 min 35 s after block 638. That is slower than the 10-minute target; long gaps are normal, since every hash attempt is an independent draw with the same tiny chance.
It confirmed 1 transactions in 0.00 MB (0.0% of the 4 million weight-unit limit). The median transaction paid 0.00 sat/vB, and all fees added up to 0.0000 BTC. With the 50.000 BTC subsidy of halving era 1, Unknown earned 50.0000 BTC for this block.
Block 639 is number 640 of 2,016 in difficulty epoch 0; 1,376 blocks remain until the next difficulty adjustment at block 2,015. The next halving is at block 210,000, 209,361 blocks after this one.
Its hash starts with 8 zeros: that is the proof of work, a number below the target that the whole network’s hashrate had to search for. Unknown found 8 blocks in the week before. Today the block has 971,988 confirmations, so it is settled beyond any practical doubt.