five gases on one wavelength scale, from the violet edge to the red
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
Wavelengths in nanometres, in air. Bar height is brightness within its own gas. The numbers come from the NIST handbook.
On 18 August 1868, during a total solar eclipse observed from Guntur in India, Jules Janssen saw a bright yellow line in the light of the solar chromosphere. In October of the same year Norman Lockyer found the same line in the spectrum of the Sun. The yellow lines of sodium were familiar to everyone and were labelled D₁ and D₂; this one stood beside them, matched neither, and was labelled D₃. Lockyer concluded that it belonged to a substance unknown on Earth and named it after Helios. The substance itself was not isolated until 1895, when William Ramsay drew the gas out of the mineral cleveite and saw the same yellow line.
The claim rested on a distance of less than one and a half nanometres, and it held, because the position of a line is a difference between two energy levels of the atom rather than a property of the sample: a spectrum does not depend on how much of the substance was taken, nor on how many million kilometres away it shines.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 11 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
from the Challenger Deep to the summit of Everest · one scale, nothing compressed
from the first synapsid to us · 320 million years on one axis
when each group appeared · five hundred million years on one axis
fifteen formulas · every letter explained beneath it