Using correct [[geometry]], but the insufficiently accurate 87° [[Datum (geodesy)|datum]], Aristarchus concluded that the Sun was between 18 and 20 times farther away than the Moon. (The true value of this angle is close to 89° 50', and the Sun's distance is actually about 400 times the Moon's.) The implicit false solar parallax of slightly under 3° was used by astronomers up to and including [[Tycho Brahe]], ca. AD 1600. Aristarchus pointed out that the Moon and Sun have nearly equal [[angle|apparent angular sizes]] and therefore their diameters must be in proportion to their distances from Earth. He thus concluded that the diameter of the Sun was between 18 and 20 times larger than the diameter of the Moon; which, although wrong, follows logically from his data. It also leads to the conclusion that the Sun's diameter is almost seven times greater than the Earth's; the volume of Aristarchus's Sun would be almost 300 times greater than the Earth.<ref>{{cite book |author=Kragh, Helge |title=Conceptions of cosmos: from myths to the accelerating universe: a history of cosmology |publisher=Oxford University Press |year=2007 |page=26 |isbn=0-19-920916-2}}</ref> This difference in sizes may have inspired the heliocentric model. |
Using correct [[geometry]], but the insufficiently accurate 87° [[Datum (geodesy)|datum]], Aristarchus concluded that the Sun was between 18 and 20 times farther away than the Moon. (The true value of this angle is close to 89° 50', and the Sun's distance is actually about 400 times the Moon's.) The implicit false solar parallax of slightly under 3° was used by astronomers up to and including [[Tycho Brahe]], ca. AD 1600. Aristarchus pointed out that the Moon and Sun have nearly equal [[angle|apparent angular sizes]] and therefore their diameters must be in proportion to their distances from Earth. He thus concluded that the diameter of the Sun was between 18 and 20 times larger than the diameter of the Moon; which, although wrong, follows logically from his data. It also leads to the conclusion that the Sun's diameter is almost seven times greater than the Earth's; the volume of Aristarchus's Sun would be almost 300 times greater than the Earth.<ref>{{cite book |author=Kragh, Helge |title=Conceptions of cosmos: from myths to the accelerating universe: a history of cosmology |publisher=Oxford University Press |year=2007 |page=26 |isbn=0-19-920916-2}}</ref> This difference in sizes may have inspired the heliocentric model. |