It glowed like a 4th magnitude star, NASA says, thanks to an explosion equivalent to 5 tons of TNT.

CNN: Bright explosion on moon visible from Earth, NASA says

Early speculation from the South Korean defense ministry is that the blast was equivalent to 7 kilotons of TNT.

FORBES: North Korea Conducts New Nuke Test

The tests, carried out at Woomera (once the British empire's equivalent of Cape Canaveral), involved a charge equivalent to six tonnes of TNT.

ECONOMIST: Bunker-busting

Most of the warheads are thought to be below 20 kilotons, equivalent to 20, 000 tons of TNT.

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Russia's defense minister said Monday that North Korea's blast was equivalent to between 5, 000 and 15, 000 tons of TNT.

NPR: Diplomat Offers Analysis of North Korea Test

By comparison, the first atomic bombs developed by the United States produced an explosion equivalent to about 19 kilotons, or 19, 000 tons of TNT, according to the U.S. Air Force.

CNN: North Koreans have made nuclear progress, experts say