Make: Geometry

To get days since the first day of winter, remember that winter starts on

December 21, more or less. There are 10 days left till the end of that year.

Then, you can look up a “day of year” calendar online (for example, at

timeanddate.com, under “other options” for calendars), which lists the days

from January 1 (which is day 1) to December 31 (day 365 or 366, depending

on whether it is a leap year). Be sure you find a calendar for your current year

so you get the leap year correction.

If you wanted to be a little more accurate, the earth’s orbit around the sun

is about 365 and a quarter days long so you could use 365.25, but we’ll keep

it simple ...