Infrara

Infrara, a powdered-wig astronomer, splits sunlight with a prism and sets a thermometer beside the spectrum.

The Physics

In 1800 William Herschel placed thermometers in the colours of a prism spectrum and found the temperature rose from violet to red. Then he moved one past the red end, where no light could be seen, and it rose further still (“Experiments on the Refrangibility of the Invisible Rays of the Sun”, Phil. Trans. R. Soc. 90, 284). The Sun emits invisible rays beyond the red: infrared.

λ_IR > λ_red ≈ 0.7 µm

• λ_IR: infrared wavelengths, about 0.7 µm to 1 mm
• λ_red: long-wavelength end of the visible spectrum

It was the first time anyone showed there is light we cannot see. Ultraviolet beyond the violet was found by Ritter the next year.

Honest caveat: The heat peak beyond red came partly from his glass prism's dispersion; with a grating the solar spectrum peaks in the visible.

On the sticker

Infrara holds a prism that fans light into a rainbow, with a thermometer standing at the side, past the coloured band. Printed text: INFRARA with the line BEYOND RED. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.