Spectrum

Spectroscope

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Body temperature

5,778 K

Kirchhoff's three laws (1859)

A hot, dense body (a bulb filament, the inside of a star) glows with a continuous spectrum — all colors.
A hot, thin gas glows only in narrow bright lines, typical of its elements.
Cooler gas in front of a hot source cuts dark lines out of the continuous spectrum — exactly where it would glow itself.

A short history of the spectrum

1666Isaac Newton splits sunlight with a prism and calls the band of colors a spectrum.
1814Joseph von Fraunhofer maps hundreds of dark lines in the Sun's spectrum.
1859Gustav Kirchhoff and Robert Bunsen create spectral analysis; they soon use it to discover cesium (1860) and rubidium (1861).
1868Pierre Janssen and Norman Lockyer see a yellow line of an unknown element in the Sun — it's helium.
1885Johann Balmer finds a formula for the visible lines of hydrogen.
1913Niels Bohr explains the hydrogen lines as an electron jumping between energy levels.

Helium was discovered on the Sun first. During an eclipse in 1868, Pierre Janssen saw a yellow line at 587.6 nm in the solar spectrum that no known element produced. Norman Lockyer named the new element after the Greek hḗlios — the Sun. On Earth, helium was isolated only in 1895.
Cesium and rubidium are named after their spectral lines. Latin caesius means “bluish gray”, and rubidus — “dark red”. Bunsen and Kirchhoff spotted these lines in the spectrum of mineral water and of the mineral lepidolite, before anyone had obtained the pure metal.
Under a low-pressure sodium streetlight the world loses its colors. The lamp shines almost entirely in two lines: 589.0 and 589.6 nm. A red car and a green lawn have nothing to reflect, so they look like shades of a single orange-yellow color.

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Identify the elements in the mystery star

Overlay the line patterns on the star's spectrum and check exactly the elements it contains. Then click “Check composition”.

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Peak at 500 nm

Set the black-body temperature so that the radiation peak λ_max falls at 500 nm (±1.5 nm). Is that close to the Sun's temperature?

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Light up the four visible hydrogen lines

In “Hydrogen atom” mode, trigger the transitions that give all four visible lines of the Balmer series. Which level must the electron drop to?

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