Strontium-87 optical clock transition
The strontium-87 optical clock transition is an energy change between two quantum states of strontium atoms that can set the timing of an optical atomic clock.
Also known as: Sr-87 clock transition
How big is it?
1.779 eV of energy
Clock-transition photon energy · measured reference
Typical recorded range: 1.773 eV to 1.785 eV.
A little perspective
Green photon energy is about 1.27 times larger on this measurement.
Green photon energy: Green photon energy is the energy carried by a single photon of green light, determined by its wavelength and fundamental physical constants.
Measurements, assumptions & sources +
Strontium-87 optical clock transition
The strontium-87 optical clock transition carries photon energy near 2.85 × 10⁻¹⁹ J. Frequency shifts depend on controlled experimental conditions.
NIST — Compact strontium optical clock
The marked clock-transition photon energy is calibrated. Unmeasured illustration details are representative.
Green photon energy
A defined 550 nm photon carries about 3.61 × 10⁻¹⁹ J, calculated from exact c and h. Green light spans a range of wavelengths, so this is one explicit wavelength specimen.
NIST — 2022 CODATA fundamental constants
The marked photon energy at 550 nm is calibrated. Unmeasured illustration details are representative.
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Why this measurement?
Why we use 1.779 eV
For comparison, this page uses clock-transition photon energy. This is labelled measured reference: an explicit comparison model rather than a claim that every example has the same value. The recorded range is 1.773 eV to 1.785 eV.
The strontium-87 optical clock transition carries photon energy near 2.85 × 10⁻¹⁹ J. Frequency shifts depend on controlled experimental conditions.
The identifying illustration and the numerical comparison remain separate. How calibrated comparisons work →
Recorded properties
Strontium-87 optical clock transition dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 1.779 eV | 1.773 eV to 1.785 eV | measured reference |
Around this scale
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These links use compatible energy records, ordered around the selected value.
Nearest lower value · Fundamental physicsCaesium-133 clock transition3.802 × 10⁻⁵ eVThe caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.Around the same scale · EnergyGreen photon energy2.253 eVGreen photon energy is the energy carried by a single photon of green light, determined by its wavelength and fundamental physical constants.Nearest higher value · EnergyVisible photon2.247 eVA visible photon is a single particle of light within the range detectable by the human eye.Sources and method
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The source records and measurement method remain available for inspection.
- NIST — Compact strontium optical clockStrontium-87 optical clock transition context and frequency scale.
There’s always another scale
Follow your curiosity.
Fundamental physicsCaesium-133 clock transition108.8 psThe caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.EnergyVisible photon2.247 eVA visible photon is a single particle of light within the range detectable by the human eye.EnergyGreen photon energy2.253 eVGreen photon energy is the energy carried by a single photon of green light, determined by its wavelength and fundamental physical constants.
EnergyHydrogen atom ground-state binding energy13.61 eVHydrogen atom ground-state binding energy is the energy needed to remove the electron from a hydrogen atom in its lowest energy state.Fundamental physicsHydrogen 21 cm hyperfine transition5.873 × 10⁻⁶ eVThis is a change in the energy state of neutral hydrogen atoms that produces or absorbs radio waves, widely used in radio astronomy.EnergyDeuterium–tritium fusion reaction energy2.82 × 10⁻¹² JDeuterium–tritium fusion reaction energy is the amount of energy released when a deuterium nucleus fuses with a tritium nucleus, producing a neutron and an alpha particle.EnergyOne-gigaelectronvolt cosmic-ray proton1.602 × 10⁻¹⁰ JA one-gigaelectronvolt cosmic-ray proton is a hydrogen nucleus travelling through space with a kinetic energy of 1 GeV.EnergyLarge Hadron Collider proton energy1.1 × 10⁻⁶ JLarge Hadron Collider proton energy is the kinetic energy carried by a single proton accelerated in the LHC.