How Long Does It Take Sunlight To Reach Earth?

The sun is the largest, most massive object in the solar system, and it is also the primary source of light for all the planets. Everyday we feel the warmth of the sun’s light, and without it, life on Earth would not exist. Interestingly, light from the sun does not reach our planet instantaneously. Rather, since the speed of light is a finite number and the sun is located about 93-million miles (150-million kilometres) away, it takes about 8-minutes for light from the sun to reach Earth.

Speed Of Light

Light is the fastest known thing in the universe, and the speed of light represents a kind of cosmic speed limit that, as far as the laws of nature suggest, cannot be surpassed. The speed of light is approximately 186,000-miles per second (300,000-kilometres per second). That is extremely fast, yet it is still a finite number, and so the further away a source of light is, the longer it takes for that light to reach our eyes. 

Distance To The Sun

The Earth orbits the sun at an average distance of 93-million miles (150-million kilometres). At this distance, there is a noticeable delay in when light emitted by the sun reaches our world. In fact, just by knowing the speed of light and the distance between the sun and Earth, you can calculate how long it takes for that light to reach us quite easily. You simply divide distance by speed and you get time. In this case, you divide 93-million miles by 186,000-miles per second to get 500-seconds, which can be converted to minutes by multiplying 500-seconds by 60, which gives you 8.3-minutes. Thus, it takes just a little over 8-minutes for light from the sun to reach the Earth. This also means that we never see the sun as it currently exists. Rather, we always see the sun as it was 8-minutes ago. For example, if the sun were to suddenly disappear, we would not notice for a full 8-minutes. 

What About The Other Planets?

Since every planet in the solar system orbits the sun at a different distance, the amount of time it takes for sunlight to reach each of them is also different. The closer a planet is to the sun, the less time it takes. For example, Mercury is the closest planet to the sun and it takes about 3.2-minutes for sunlight to reach it. For Venus it’s about 6-minutes, and for Mars it takes 12.6-minutes. Thus, it takes less than 13-minutes for sunlight to reach all of the inner planets in our solar system. However, it takes much longer for sunlight to reach the gas giants. It takes 43.2-minutes for sunlight to reach Jupiter, and 79.3-minutes for it to reach Saturn. For Uranus, it takes 159.6-minutes, and for Neptune, it takes just over 4-hours. 

Time it Takes for Sunlight to Reach Each Planet