The star nearest to us, apart from the sun, is called Proxima Centauri and is about four light-years away from us (meaning light from that star takes about four years to reach us) or about 40 trillion kilometres. In comparison, light from the sun takes only about eight minutes to reach us. The stars seem to be spread across the entire sky but are actually concentrated in one particular band, which we call the Milky Way galaxy. We now know that the Milky Way—our galaxy is not the only galaxy. In 1924, the American astronomer Edwin Hubble found many others, with huge areas of empty space in between them. But these galaxies were so far away that they appeared not to move at all and their distance from us could not be directly measured.
Scientific developments have enabled us to study and observe these stars and galaxies which would not have been possible at the time when the Quran was revealed. Another way to measure the distance of a star or galaxy from us is by its brightness. The temperature of a star can also be calculated by focusing a telescope on a distant star and passing its light through a prism. This light splits up into different colours—called the star’s spectrum. Different stars have different spectra, but a specific temperature shows a specific spectral pattern. If we know the temperature of a star, and therefore its luminosity, and its apparent brightness, its distance from us can be calculated.
As astronomers began to study these distant galaxies, they discovered that the light from each galaxy showed the same spectral pattern. To understand the implications of this, we must first understand that light travels in waves. The size of the wave, called wavelength, determines its colour. Visible light consists of seven colours: red—which has the longest wavelength and therefore the largest waves, orange, yellow, green, blue, indigo, and violet—which has the shortest wavelength and therefore the smallest waves.