It takes light from the Sun 8 minutes and 20 seconds to reach us on Earth – on average.
That’s the simple, straightforward answer – but whatever the razor-toting Mr Occam may tell you, the simple, straightforward answer seldom tells you the whole truth.
In this case, there are two factors that complicate the picture.
Firstly, the answer that it takes light from the Sun 8m 20s to reach Earth is derived by dividing the distance from the Sun to Earth – around 150 million kilometres – by the speed of light, which is around 300,000 km/s (kilometres per second).
That’ll give you a journey time of some 500 seconds, or eight minutes 20 seconds.
However, Earth’s orbit around the Sun is slightly elliptical rather than perfectly circular.
So the actual distance between our planet and the big fiery globule of burning gas that gives Earth light and heat can be anywhere from 147 to 152 million kilometres.
So light's actual journey time from the Sun to Earth can be anywhere from 490 to 507 seconds, or 8m 10s to 8m 27s.
Secondly, the answer above is how long it takes for any given photon of light to journey from the Sun’s surface to that of Earth – but that’s not the whole story.
Photons of light, you see, aren’t formed at the Sun’s surface: they’re ‘made’ deep inside the star and because the Sun is, to quote Douglas Adams, "vastly, hugely, mind-bogglingly big".
It can take them thousands or even tens of thousands of years to reach the surface of the Sun, before they embark on their 8m 20s journey to Earth.
This means that while the photons of light coming your computer or screen that enable you to read this article are just nanoseconds old, those that hit your eyes when you step outside on a sunny day actually began their journey several thousand years ago.
Which is a bit longer than 8m 20s.
And which, as a side note, is why shadows are inherently funny.
Imagine being born inside a star, spending thousands of years fighting your way to its surface, bravely traversing millions of miles of interplanetary space and battling through Earth’s atmosphere all the way down to the ground.
Only, after all that effort, to have your plans thwarted by a lamp post or wheelie bin!
