Cesium News

YES

No decision made in 2026 conference

Second defined by a (dynamic) weighted sum of atomic transitions

Second defined by a (fixed) weighted sum of atomic transitions

Decision made to not redefine the second

Second defined by 87Sr 698nm transition

Second defined by fixing the Rydberg constant

Second defined by 171Yb 578nm transition

Second defined by 199Hg 265nm transition

Second defined by 27Al+ 267nm transition

Second defined by 199Hg+ 282 nm transition

Second defined by 171Yb+ (E2) 436nm transition

Second defined by 171Yb+ (E3) 467nm transition

Second defined by 88Sr+ 674nm transition

Second defined by 88Sr 698nm transition

Second defined by 40Ca+ 729nm transition

Second defined by 87Rb 6.8GHz microwave transition

The cesium 133 F=3 <-> F=4 hyperfine microwave transition (no change)

Any system based on weighted averages of uncertainty or timekeeping contributions

The strontium 87 1S0 <-> 3P0 optical transition

The ytterbium 171 1S0 <-> 3P0 optical transition

Any other optical transition in ions

Any other optical transition in neutral atoms

NO

Hydrogen

Helium

Lithium to neon

Sodium to argon

Potassium to iron

Cobalt to xenon