Sekund
A Sekund oda Sekundn is de Basisoaheid vo da Zeid im internationain Oaheidnsystem (SI). A Sekund dauad eppa an Heazschlog lang.

A Stund hod 60 Minutn und a Minutn hod 60 Sekundn. Friacha hod ma a Sekundn nochn middlan Sunnadog definiad. Ob anno 1960 ois Epfemeridnsekund iba de Daua vo an tropischn Joar.

Seit 1967 gibts de Atomsekund. De is definat ois as 9 192 631 770-foche vo da Periodndaua vo da Strohlung, de wo en Ibagang zwischn de boadn Hyperfeinstruktuaniveaus vom Grundzuastan vo de Atome vom Nuklid Caesium-133.

Im Netz

 National Physical Laboratory: Trapped ion optical frequency standards 
 High-accuracy strontium ion optical clock; National Physical Laboratory (2005)
 NIST: Definition of the second; notice the cesium atom must be in its ground state at 0 K
 Official BIPM definition of the second
 The leap second: its history and possible future
 Accuracy of the time — Astronoo

Beleg 

Physikalische Größe