_In Semi-Diameters of Earth._ Moon 64⅛ Mercury 167 Venus 1120 Sun 1220 Mars 8876 Jupiter 14,405 Saturn and Stars 20,110 In this, the moon’s distance is approximately correct, but the sun’s is not much more than one-twentieth of its true value. To set the stars at a distance of only twenty thousand times Earth’s semi-diameter seems to us to bring them very close,[67] but they would still be beyond measurement by naked eye methods, so it is no contradiction to Alfraganus’ earlier statement that Earth is a point compared with the heavens. ------------------------------------------------------------------------ [67] Earth’s diameter, and even Earth’s distance from the sun, is too small a unit. Light, travelling 186,000 miles a second, takes 4¼ years to reach us from the nearest star. ------------------------------------------------------------------------ The Arabs also believed that they had succeeded in measuring the apparent diameters of the planets and even of the points of light which are all we can see of stars, so Alfraganus gives the accepted sizes of all. I give them below in descending order of size. The modern values in the third column show how false were the results obtained by this mistaken method. DIAMETER: EARTH = 1. _Alfraganus. Modern Values._ Sun 5½ 109½ The 15 first-magnitude { Arcturus, Sirius, stars 4¾ { Spica, and others, much { larger than the sun. Jupiter 4⁹/₁₆ 11 Saturn 4½ 9 Other stars, in order of { Various. Some certainly magnitude, 2nd to 6th ... { larger than the sun. Mars 1⅛ ½ Earth 1 1 Venus ³/₁₀ ⁹/₁₀ Moon ⁵/₁₇ ¼ Mercury ¹/₁₈ ⅓ In the above table the size of the moon (whose parallax had been found by the Greeks) is the only one which is nearly right. The sun is far too small, and so are the stars. We cannot yet know with certainty the diameter of any star, but they are all comparable with the sun, and many are enormously larger.[68] As their distances are all different, some of the brightest may be comparatively small, and some of the faintest the largest of all.