Here’s a question… how long does it take sunlight to reach Earth? This may appear to be an odd question, but consider it. The sun travels at the speed of light. Photons emitted from the Sun’s surface must traverse the vacuum of space to reach our eyes.
How long does it take sunlight to reach Earth? – Answers
The distance light travels in one second is 186,000 miles. That means sunlight travels from the Sun to the Earth in an average of 8 minutes and 20 seconds.
It would take a little more than 8 minutes for you to realize it was time to put on a sweater if the Sun suddenly vanished from the Universe (not that this could actually happen, don’t worry).
Here’s how it works. We orbit the Sun at a distance of approximately 150 million kilometers. Light travels at a speed of 300,000 kilometers per second. The result of dividing these is 500 seconds, or 8 minutes and 20 seconds.
The distance between the Earth and the Sun
varies throughout the year. At the beginning of spring, when the Earth is closest to the Sun, it takes about 491 seconds for light to travel from the Sun to the Earth. By summer, when the Earth is furthest away from the Sun, it takes 511 seconds for light to reach us.
But the story of light gets even more interesting when you think about the journey light needs to make inside the Sun.
You’re probably aware that photons are produced by fusion reactions within the Sun’s core. They begin as gamma radiation and then are emitted and absorbed countless times in the Sun’s radiative zone, circling the massive star before reaching the surface.
What you probably don’t know
is that the photons that hit your eyes were created tens of thousands of years ago and it took that long for them to be emitted by the Sun.
Once they escaped the surface, it was only a short 8 minutes for those photons to cross the vast distance from the Sun to the Earth.
Looking out into space is actually looking backward in time.
The light emitted by your computer is only nanoseconds old. The light reflected from the Moon’s surface travels only a fraction of a second to Earth. More than 8 light-minutes separate us from the Sun. As a result, if the light from the nearest star (Alpha Centauri) takes more than four years to reach us, we are seeing that star four years in the past.
There are galaxies millions of light-years away, which means the light we’re seeing left the surface of those stars millions of years ago. M109, for example, is approximately 83.5 million light-years away.
If aliens lived in those galaxies and had powerful enough telescopes, they could see Earth as it once was. They may even see dinosaurs on the surface.