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 · clock-transition photon energy
Clock-transition photon energy · measured reference
Typical recorded range: 1.773 eV to 1.785 eV.
A little perspective
Strontium-87 optical clock transition vs Green photon energy: energy comparison
The energy of a green photon is about 1.27 times the clock-transition photon energy of the strontium-87 optical clock transition.
ENERGY STORED OR TRANSFERRED
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.
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
Clock-transition photon energy: 1.779 eV; measured reference; range 1.773 eV–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.
NIST — Compact strontium optical clock
The marked clock-transition photon energy is calibrated. Unmeasured illustration details are representative.
Green photon energy
Photon energy at 550 nm: 2.253 eV; derived from defined specimen; range 2.247 eV–2.259 eV.
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.
Use the visual comparison to explore its scale, then check the measurements and sources.
Change your perspective
Put it next to…
Choose a suggestion to redraw the comparison, or open its page to learn what it is.
Why this measurement?
Why we use 1.779 eV
We compare the clock-transition photon energy of the strontium-87 optical clock transition. This is a measured value; check the notes for its source and scope. 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 picture identifies the subject; the diagram compares the recorded values. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 1.779 eV | 1.773 eV to 1.785 eV | measured reference |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valueFundamental physicsCaesium-133 clock transition3.802 × 10⁻⁵ eVSingle-photon transition energyThe 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 scaleEnergyGreen photon energy2.253 eVPhoton energy at 550 nmGreen photon energy is the energy carried by a single photon of green light, determined by its wavelength and fundamental physical constants.Nearest higher valueEnergyVisible photon2.247 eVEnergyA visible photon is a single particle of light within the range detectable by the human eye.Sources and method
Want to check the number?
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.