Why does the Sun follow you?

Have you ever noticed that when you are in a car, or a bus, travelling on a straight road, the Sun appears to move right along with you? While telephone poles and trees close to the road, whiz past in the blink of an eye, the Sun is always visible throughout the journey. No matter how fast you drive, you just cannot leave the Sun behind.

Strangely enough, the trees nearer the road disappear from your range of vision more quickly than the trees further off. Why is this so? Our eyes have a certain ‘range’ of vision. You can see things only within that range. For instance, you cannot see objects behind your head. This field of vision widens out from the point where you are.

Objects further away are visible for a longer period, even as your car whizzes by. To understand what the range of vision is, draw a triangle as in the picture and name the corners A, B and C, such that the distance between A and B is equal to the distance between A and C. The point A indicates your position.

Now draw a line DE in the triangle, parallel to BC, such that ADE forms a smaller triangle ‘within’ ABC. Look at the triangle. You will see that BC is longer than DE. This means that your field of vision at any point on the line BC is wider than what you can see on any point on the line DE. This means that your line of vision widens as the distance from your eyes (point A) increases.

As a result, objects further away from you stay longer in your field of vision since the range is larger than nearby objects. And very distant objects appear to be in the same position for a long time. The Sun is 149,597,870 kilometres away from the Earth. That is a huge distance, so it seems to stay in the same place, in relation to your car, no matter how fast you travel.

The only thing that travels fast enough to make the Sun appear to move in the sky is the Earth itself. If you consider a point on the equator, the Earth rotates on its axis at a speed slightly more than 1,600 kilometres per hour. The equator is an imaginary circle on the surface of the Earth which is at a equal distance from the poles and divides the Earth into two parts, the northern and southern hemispheres.

However, the Earth is huge, and despite rotating at such an incredible speed, it takes 23 hours, 56 minutes and 4.1 seconds to complete one full rotation. On an average, the Earth takes 24 hours to make one complete rotation and as it moves on its axis, the Sun appears to move along the horizon, rising from the East, moving overhead and finally setting on the West. The length of one day is averaged over the period of a year.