VENUS - The Second Planet
Venus, the second closest planet to the sun, is a yellow color; it is the third after the sun and moon in brightness in our night sky. Like Mercury, Venus goes through all the lunar phases, as Galileo first observed in 1609.
Since it has a larger orbit than Mercury, Venus swings farther out from the sun as viewed from the earth, about 47°, or twice as far as Mercury. Venus remains visible as an evening star in the western sky or as a morning star in the eastern sky for weeks at a time. Although Venus comes slightly closer to the earth than Mars does, we cannot see features then because its dark hemisphere is turned toward us.
Venus's diameter, mass, and density are slightly less than those of the earth. Its mass is 80 or so percent of that of the earth. Venus possesses a mean density over 5 grams per cubic centimeter, suggesting that its internal structure is similar to that of the earth and Mercury.
The most striking feature about Venus is a cloud cover that totally hides the surface in visible and infrared radiation. The clouds themselves are almost totally featureless in the visible wavelengths, where the planet appears bland and featu reless with a pale yellow color.
Venus's rotation was a mystery that eluded solution by optical or spectroscopic observations because of this cloud cover and the planet's slow rate of rotation. But Doppler shifts noted in radar observations solved the problem. The planet rotates in a retrograde direction, with its axis of rotation inclined only 2° from the perpendicular to its orbital plane. (Retrograde here means a direction of rotation reversed from that of revolution about the sun.) The period of rotation as determined from radar measurements is 243 days, 18 days longer than its orbital period. Because its revolution period is about 225 days, just slightly shorter than the rotation period, the Venusian day is 117 days long, with 58.5 days of sunlight and 58.5 days of darkness. Thus the sun rises on the western horizon and sets approximately twice during the Venusian orbit with respect to the earth.
Venus, the second closest planet to the sun, is a yellow color; it is the third after the sun and moon in brightness in our night sky. Like Mercury, Venus goes through all the lunar phases, as Galileo first observed in 1609.
Since it has a larger orbit than Mercury, Venus swings farther out from the sun as viewed from the earth, about 47°, or twice as far as Mercury. Venus remains visible as an evening star in the western sky or as a morning star in the eastern sky for weeks at a time. Although Venus comes slightly closer to the earth than Mars does, we cannot see features then because its dark hemisphere is turned toward us.
Venus's diameter, mass, and density are slightly less than those of the earth. Its mass is 80 or so percent of that of the earth. Venus possesses a mean density over 5 grams per cubic centimeter, suggesting that its internal structure is similar to that of the earth and Mercury.
The most striking feature about Venus is a cloud cover that totally hides the surface in visible and infrared radiation. The clouds themselves are almost totally featureless in the visible wavelengths, where the planet appears bland and featu reless with a pale yellow color.
Venus's rotation was a mystery that eluded solution by optical or spectroscopic observations because of this cloud cover and the planet's slow rate of rotation. But Doppler shifts noted in radar observations solved the problem. The planet rotates in a retrograde direction, with its axis of rotation inclined only 2° from the perpendicular to its orbital plane. (Retrograde here means a direction of rotation reversed from that of revolution about the sun.) The period of rotation as determined from radar measurements is 243 days, 18 days longer than its orbital period. Because its revolution period is about 225 days, just slightly shorter than the rotation period, the Venusian day is 117 days long, with 58.5 days of sunlight and 58.5 days of darkness. Thus the sun rises on the western horizon and sets approximately twice during the Venusian orbit with respect to the earth.
