The words ‘degree’ and ‘degrees’ are used over a hundred times in Project Hail Mary (more on that later) but the symbol ° is used 12 times, mostly but not exclusively on display readouts.

Both the words and the symbol are used for both angle and temperature in the book.

The Latin gradus (from which the word degree comes) referred to a step in a graded system. The use of ° for angles (rather than writing gradus) was popularized by Brahe and Kepler.

Temperature scales also started off using the word gradus but later also adopted °.

The symbol was not included in the original 7-bit ASCII character set but in 1987 was assigned the code point 0xB0 (176 in decimal) in ISO/IEC 8859. It thus became part of Unicode as U+00B0 with the name DEGREE SIGN.

When used for angle, the symbol directly follows the number with no intervening space.

When used for temperature, convention varies with some organizations prescribing a space before the symbol (but no space before the following C or F) and others prescribing no space at all.

In Project Hail Mary the latter is followed and so we get things like “39.7°C”.

Oddly there are 3 times when °c is used (with lowercase ‘c’) (04.031, 04.033, and 04.244), always read off a display, and in each case the temperate 96.415°c.

Another 5 times, ° is used with uppercase F (06.141) or C (06.141, 14.181, a display readout in 22.061, and 27.006)

The remaining 4 occurrences of ° refer to angle and are all display readouts (08.096, 08.113 twice, 08.118)