Dante and the early astronomers . ickly, so that she rapidly passes many posts,although all the time she is being carried backwardswith them: she is the moon. Children run backwardsand forwards: they are the planets. Finally, if all 20 APPARENT MOVEMENTS OF these people are also constantly crossing the platfoimslowly from right to left and back again, theirmovements will be oblique to the platform movementand will imitate the north and south movements ofsun, moon, and planets. It is in this fashion that the movements of the skiespresent themselves to careful observers on this seem-ingly statio
Dante and the early astronomers . ickly, so that she rapidly passes many posts,although all the time she is being carried backwardswith them: she is the moon. Children run backwardsand forwards: they are the planets. Finally, if all 20 APPARENT MOVEMENTS OF these people are also constantly crossing the platfoimslowly from right to left and back again, theirmovements will be oblique to the platform movementand will imitate the north and south movements ofsun, moon, and planets. It is in this fashion that the movements of the skiespresent themselves to careful observers on this seem-ingly stationary earth; and in the youth of the worldthese apparent movements were believed to be ancients thought that the sky was actuallyrevolving round a steadfast earth, while the sun andmoon and certain other wandering stars had inaddition various motions peculiar to themselves. The table of periods which follows (see pp. 22-23)will be found useful for occasional reference. Someof the terms used will be explained later. CANCER. CAPRlC Fig. 5. Diagram illustrating Synodic and Sidereal Periods. The arrows show the direction of the Moons monthly and the Suns yearly revolutionsin the zodiac, as seen from Earth. When the Moon is opposite the Sun, for instance in Libra while he is in Aries, she isfull. In 27J days she returns to the same place among the stars, and this is a siderealMONTH. But the Sun meanwhile has moved into Taurus, and not until the Moon ha:,reached Scorpio, opposite to him, will she be full again, and complete her synodicMONTH (29i days). 22 APPARENT MOVEMENTS OF REVOLUTIONS OF SUN, MOON, AND PLANETS AS SEEN FROM THE EARTH. Tropical Solar Year: period from one I>a,ys. ffrs. Mins. equinox to another, or from one summer solstice to the next, &c. 365 5 48 45*5(Our civil year is based on this). Sidereal Year: period between twosuccessive returns of the sun to anystar on his path - - - . 365 6 9 8-9 The difference between these two kinds of year is due
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