A day is how long it takes the sun to come back overhead.

Doesn’t happen on the sun, unless you’re standing upside down, in which case days on

the sun are infinitesimally short and your hair is on fire.

But maybe a day is how long it takes to spin around relative to the distant stars, in which

case different parts of the sun have different days because it’s a big ball of flowing,

gassy plasma and different parts rotate at different rates: relative to distant stars,

the sun’s equator rotates once every 24 and a half earth days, while near the poles

it rotates roughly every 34 earth days.

Or maybe a day is simply eighty six thousand and four hundred seconds, in which case a

day on the sun is slightly longer than a day on the earth due to gravitational time dilation.

Or maybe a day is the time a human can survive without breathing, times 360, in which case

a day on the sun is… definitely your last.