A year is the time it takes for a planet to orbit around the sun once. Further, a day is the time it takes for a planet to revolve once around its rotational axis.

The progress bar indicates how far along a planet has already progressed in the current year.

Note that Mercury and Venus are both tidally locked to the sun and thus experience only 1 or 2 solar days per year respectively.


Planetary orbital data was obtained from jpl.nasa.gov. Dwarf planet orbital parameters according to wikipedia.

We use 62138156134 (magic constant) + unix timestamp (seconds since unix epoch) to calculate the amount of seconds that have passed since 1.1.0001 AD.

Given the orbital period we can calculate the current year:

n_years = t_passed / orbital_period

Days are calculated from the remainder of this division:

n_days = (remainder * orbital_period) / len_day

According to simple tests, the date on Earth will not be off by more than 1 day during the next few years. Have a look at the source for more details.


Made in 8370 AD (Mercury) by Oliver Dressler