<P> According to the "angle of regard" hypothesis, the Moon illusion is produced by changes in the position of the eyes in the head accompanying changes in the angle of elevation of the Moon . Though once popular, this explanation no longer has much support . Looking through one's legs at the horizon moon does reduce the illusion noticeably, but this may be because the image on the retina is inverted . Raising the eyes or tilting the head when in an upright posture gives only a very small reduction in the illusion . </P> <P> Immanuel Kant refers to the Moon illusion in his 1781 text Critique of Pure Reason, when he writes that "the astronomer cannot prevent himself from seeing the moon larger at its rising than some time afterwards, although he is not deceived by this illusion". Schopenhauer (1813) was cited above . Wade shortly summarizes historical references to the Moon illusion starting with Aristotle; he lists quotes by Aristotle (~ 330 BC), Ptolemy (~ 142, 150), Ibn al - Haytham (Alhazen) (1083), John Pecham (~ 1280), Leonardo da Vinci (~ 1500), René Descartes (1637), Benedetto Castelli (1639), Pierre Gassendi (1642), Thomas Hobbes (1655), J. Rohault (1671), Nicolas Malebranche (1674), William Molyneux (1687), J. Wallis (1687), G. Berkeley (1709), J.T. Desaguliers (1736), W. Porterfield (1737), R. Smith (1738), C.N. Le Cat (1744), D. Hartley (1749), Thomas Young (1807), and Carl Friedrich Gauss (1830). </P>

When a full moon rises the size appears to be larger than when it is directly overhead. why