Other astronomical achievements of the Babylonians were the following.  They accomplished a catalogue of the fixed stars, of which the Greeks made use in compiling their stellar tables.  They observed and recorded their observations upon occultations of the planets by the sun and moon.  They invented the gnomon and the polos, two kinds of sundial, by means of which they were able to measure time during the day, and to fix the true length of the solar day, with sufficient accuracy.  They determined correctly within a small fraction the length of the synodic revolution of the moon.  They knew that the true length of the solar year was 365 days and a quarter, nearly.  They noticed comets, which they believed to be permanent bodies, revolving in orbits like those of the planets, only greater.  They ascribed eclipses of the sun to the interposition of the moon between the sun and the earth.  They had notions not far from the truth with respect to the relative distance from the earth of the sun, moon, and planets.  Adopting, as was natural, a geocentric system, they decided that the Moon occupied the position nearest to the earth; that beyond the Moon was Mercury, beyond Mercury Venus, beyond Venus Mars, beyond Mars Jupiter, and beyond Jupiter, in the remotest position of all, Saturn.  This arrangement was probably based upon a knowledge, more or less exact, of the periodic times which the several bodies occupy in their (real or apparent) revolutions.  From the difference in the times the Babylonians assumed a corresponding difference in the size of the orbits, and consequently a greater or less distance from the common centre.

Thus far the astronomical achievements of the Babylonians rest upon the express testimony of ancient writers—­a testimony confirmed in many respects by the monuments already deciphered.  It is suspected that, when the astronomical tablets which exist by hundreds in the British Museum come to be thoroughly understood, it will be found that the acquaintance of the Chaldaean sages with astronomical phenomena, if not also with astronomical laws, went considerably beyond the point at which we should place it upon the testimony of the Greek and Roman writers.  There is said to be distinct evidence that they observed the four satellites of Jupiter, and strong reason to believe that they were acquainted likewise with the seven satellites of Saturn.  Moreover, the general laws of the movements of the heavenly bodies seem to have been so far known to them that they could state by anticipation the position of the various planets throughout the year.