How long does light from the Sun take to reach Earth?

Light from the Sun takes approximately 8 minutes and 20 seconds to reach Earth.

The speed of light in a vacuum, such as space, is approximately 299,792 kilometres per second. This is often rounded to 300,000 kilometres per second for simplicity. The distance between the Earth and the Sun, known as an Astronomical Unit (AU), is about 150 million kilometres.

To calculate the time it takes for light to travel from the Sun to Earth, we divide the distance (150 million kilometres) by the speed of light (300,000 kilometres per second). This gives us a time of approximately 500 seconds, which is equivalent to 8 minutes and 20 seconds.

However, it's important to note that this is an average. The Earth's orbit around the Sun is not a perfect circle, but an ellipse. This means that the distance between the Earth and the Sun varies throughout the year. At its closest, known as perihelion, the distance is about 147 million kilometres. At its furthest, known as aphelion, the distance is about 152 million kilometres. Therefore, the time it takes for light to reach Earth from the Sun can vary by up to about 8 seconds.

This concept is fundamental to understanding many aspects of astronomy and physics. For example, when we look at the Sun, we're actually seeing it as it was 8 minutes and 20 seconds ago. Similarly, when we look at distant stars, we're seeing them as they were many years ago, because of the time it takes for their light to reach us. This is often referred to as 'looking back in time'.