Why does it take light so long to reach us from distant galaxies?
Well, for the same reason why it takes time for us to travel from one place to another.
The space between one place and another is called ‘distance’ and if a person needs to move from one place to another, it can never be instantaneous.
There is a ‘time of starting’ from one place and a ‘time of arrival’ at the other place that will be the ‘elapsed time’ or time spent in travelling.
The ’elapsed time’ in travel from one place to another depends on the ‘speed’ of travel.
For example, if the distance from point A to point B is 100 kilometers, and if a person travels on a bicycle at about 10 km per hour, the travel time is 10 hours.
You can see that distance ÷ speed gives you the time taken for travel. If the person uses a car and travels at a speed of 50 km per hour, then the time taken is 2 hours. This shows, higher the speed, shorter the time taken for travel.
You stated ‘distant galaxies’ in your question. Do you have an idea how far away are galaxies from Earth?
The distance to stars and galaxies is not stated in kilometers because the number will be too large to comprehend.
The distance is stated in ‘light years’ meaning, the distance that light covers in one year and the speed of light happens to be 299,792.458 kilometers per second.
You can multiply this number by 60 to get kilometers per minute, and multiply that by 60 again to arrive at the kilometers per hour just to see how big the number becomes.
The nearest galaxy to Earth is the Andromeda which is 2.5 million light years away from Earth.
So you see, it means, it is so far away that light — at the speed of 299,792.458 kilometers per second takes 2.5 million years to travel from Andromeda to the Earth.
Therefore, light takes so long to reach us from distant galaxies because of the vast distances involved.
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