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Where Do They Hide?

Golden ratio: Sunflower seed arrangements and other examples of phyllotaxis can produce spiral patterns related to Fibonacci numbers and the golden ratio. The golden ratio also appears naturally in the geometry of the pentagon and pentagram.

Why “Metallic”?

Mathematician Vera de Spinadel gave this family its name in the late 1990s. She extended the gold-and-silver naming tradition into a full sequence: gold for n=1, silver for n=2, bronze for n=3, and so on. The names are poetic, not literal. These numbers have nothing to do with the metals themselves.

How many finished grids actually exist?

Here is a number that will surprise you. There are 6,670,903,752,021,072,936,960 different ways to fill a standard 9 x 9 Sudoku grid. That is more than 6.67 sextillion possible completed grids. It is hard to picture a number that large. Even if you completed a different Sudoku grid every second, without ever taking a break, you still would not finish them all in your lifetime.

What is ultraviolet radiation?

Sunlight is not just light. It is a spectrum, a continuous range of wavelengths. The part we can see, called visible light, spans roughly 380 to 700 nanometers (nm). Just beyond the violet edge of this range lies ultraviolet radiation, or UV, which stretches from about 100 to 400 nm. We cannot see it, but it has a strong effect on our skin and health.

Where does E(λ) come from?

E(λ) is not assumed or invented. It is measured or modelled from physical reality using one of three approaches. The most direct method is a ground-based spectroradiometer, an instrument that measures actual solar irradiance at each wavelength in real time. This gives highly accurate readings tied to the exact local conditions at the moment of measurement.