What is Wien's displacement law?

Wien's displacement law states that the peak wavelength of thermal (blackbody) radiation λ_max is inversely proportional to the absolute temperature T: λ_max × T = b, where b = 2.897773 × 10⁶ nm·K. A hotter star emits most of its light at a shorter (bluer) wavelength; a cooler star peaks at a longer (redder) wavelength.

Why does a star appear a different color than its peak wavelength?

Stars emit across a broad continuous spectrum. The peak wavelength determines the dominant color, but the mix of all emitted wavelengths reaching your eye produces a somewhat washed-out color — typically from blue-white (hot) to orange-red (cool). The color swatch here is the pure perceived hue for that single wavelength, not the integrated color of the full spectrum.

What wavelength should I enter for the Sun?

The Sun's effective surface temperature is about 5,778 K, corresponding to a peak wavelength of roughly 502 nm (green-yellow). Despite this, the Sun appears white-yellow because it emits significant red, orange, and blue light that blends into white at the eye.

Are real stars perfect blackbodies?

No. Stars have complex atmospheres that produce absorption lines and deviate from a pure Planck curve. Wien's law applied to the photosphere temperature gives a good first approximation, but detailed stellar models account for opacity, limb darkening, and non-LTE effects. For most purposes, the blackbody approximation is accurate to within a few percent.

What is the spectral class shown?

The Harvard spectral classification groups stars by temperature: O (>30,000 K, blue), B (10,000–30,000 K, blue-white), A (7,500–10,000 K, white), F (6,000–7,500 K, yellow-white), G (5,200–6,000 K, yellow), K (3,700–5,200 K, orange), M (<3,700 K, red). Each class is subdivided 0–9 from hottest to coolest.

Blackbody Temperature of a Star

Name: Blackbody Temperature of a Star
Availability: InStock
Author: Nham Vu

Enter a star's peak emission wavelength (in nanometers) to estimate its surface temperature via Wien's displacement law and see its visible color.

Peak Wavelength Input

Peak emission wavelength (nm)

Visible range: 380–700 nm | Infrared: >700 nm | UV: <380 nm

Known stars

Wien's Displacement Law

T = b / λ_max

b = 2,897,773 nm·K (Wien's constant)

Temperature Results

Enter a peak wavelength to see the estimated temperature.

Visible Spectrum Position

380 nm (UV) 700 nm (IR)

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Summary

Enter a star's peak emission wavelength (in nanometers) to estimate its surface temperature via Wien's displacement law and see its visible color.

How it works

Enter the peak emission wavelength of the star in nanometers (nm). You can use known values or measure from a stellar spectrum.
The calculator applies Wien's displacement law: T = b / λ_max, where b = 2,897,773 nm·K.
The resulting temperature in kelvin is displayed along with its equivalent in Celsius.
If the peak wavelength falls in the visible range (380–700 nm), a color swatch shows the approximate perceived color.
The tool also maps the temperature to the Harvard spectral classification (O, B, A, F, G, K, M) and shows a well-known example star.

Use cases

Determine a star's surface temperature from spectroscopic peak-wavelength data.
Cross-check stellar classification assignments in astronomy coursework.
Visualize how a star's color relates to its temperature across the HR diagram.
Explore the relationship between spectral peak and surface temperature for stellar models.
Quickly convert observed peak wavelengths from infrared surveys to equivalent temperatures.
Verify blackbody physics calculations for physics or astrophysics students.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu