VENUS. A planet whose orbit is between those of the earth and Mercury. Her mean dis tance from the sun is 67,200.000 miles. The eccentricity of her orbit is smaller than that of tiny other planet, being only 0.07; and therefore her greatest and least distance from the sun dif fer by only about 940,000 miles. She performs her sidereal revolution in 224.7 days, in an orbit whose plane is inclined 3° to that of the ecliptic, but her synodical revolution requires much more time, 584 days. Between inferior conjunctions and the next superior conjunction Venus is a morning star, and between superior conjunctions and the next inferior conjunction she is an evening star. Her diameter is about 7700 miles; so that her volume is about 0.92 of that of the earth, and her mass is nearly 0.82 of that of the earth. In the telescope Venus presents phases similar to those of our moon, varying from a mere sickle of light to a complete circle. The brilliancy of the planet is at times
very great, rendering her visible easily in day light. The maximum brightness occurs thirty six clays on either side of inferior conjunction, the condition of maximum depending on the planet's phase and proximity to the earth.
The rotation period is still much in doubt, for the surface markings arc inconspicuous, and it is only by showing these markings that we can fix the period. Some astronomers (Schiaparelli and Powell) think the period is one of 225 day;, the same as the orbital period, and that. Venus, like our moon, always turns the same side toward the centre of the orbit. Other astronomers fix the period as approximately equal to that of the earth, namely, 24 hours. Venus probably has some sort of an atmosphere, but no satellites are known. See TRANSIT or VENUS ; PLANETS ; SO LAR SYSTEM.