Venus is the second closest of the major planets to the Sun and it takes 224.7 Earth days to complete its orbit around the Sun. The planet is named for the Roman goddess of love and it is the only major planet named for a female figure. Viewing the sky from Earth, Venus is the brightest natural night time object other than the Moon. Venus is brightest just before sunrise or just after sunset, and, for this reason, it is also called the Morning star and the Evening star.
Venus is classified as a terrestrial planet, i.e. an earth like planet, one of four so classified in the solar system (others are Mercury, Mars and Earth itself), a terrestrial planet being defined as one that, like Earth, is composed of a core, (whether liquid, solid or molten), a mantle and a crust.
Venus’ similarities to Earth, however, are considerably more than just both of them being terrestrial planets. In terms of size (Venus’ equatorial diameter is only 650 kilometres less than Earth’s), mass (81.5 percent of Earth’s), gravity (86 percent of Earth’s), time taken to complete a revolution round the Sun and escape velocity, i.e. the velocity required for a body to break away from the gravitational pull of another body, (just over 10 km/h for Venus, compared with just over 11.25 km/h for Earth), no other planet replicates Earth in the manner of Venus. Not surprisingly, Venus is often described as Earth’s twin.
But, like all twins, there are clear differences, assertions of individuality. Venus’ atmosphere is considerably denser than Earth’s, atmospheric pressure at the surface being more than 90 times that on the Earth’s surface (one would have to go a kilometre or more under the sea to face such pressures on Earth). In addition, the gases that make up the atmosphere constitute a witches’ brew from the viewpoint of organisms that have evolved on Earth. Carbon dioxide is the most common gas with small additions of nitrogen. Further, clouds of sulphur dioxide and sulphuric acid floating above the thick carbon dioxide layer combine to produce the most intense greenhouse effects in the solar system. In addition, because of the reflective properties of the gasses that make up the atmosphere (60 percent of the sunlight that reaches Venus is reflected back into space), visibility on the surface is less than on Earth’s surface, in spite of the fact that Venus is much closer to the Sun than Earth is. The intense greenhouse effect actually makes Venus the hottest planet in the solar system, with temperatures in the region of over 400 degrees centigrade; hotter, even, than Mercury, which is considerably closer to the Sun than Venus is.
The planet’s axial tilt is minimal, less than 3 degrees compared to Earth’s 23 degree tilt, and, given its size has a much smaller magnetic field than would be expected. The explanation for this is that it is believed that Venus’ core is considerably less liquid than is Earth’s; perhaps even solid. Current thinking is that the more liquid a planet’s core is, the greater the magnetic field that it generates.
The question arises, and it is a valid one, as to whether these “facts” about Earth’s twin are indeed facts or just guesstimates; informed guesstimates, perhaps, but guesstimates nonetheless. We can say with some confidence that the facts, as we know them today, outnumber the guesstimates. Before the 20th century, telescopic study of Venus was hampered by the fact that its atmosphere was largely opaque to radiation in the visible spectrum; even the use of infrared did not change matters much. However, with the development of ultraviolet and radar techniques, Earth based observers were better able to determine what the conditions are on Venus. But our views are not only based on Earth based observations. Since the early sixties of the previous century, numerous space probes have visited Venus, and some have even landed on the planetary surface. The reports from these probes have enhanced our understanding of our nearest major planetary neighbour.
Based on Earth based observations and the reports of the probes that have visited the planet, we know that Venus’ surface is mainly plain broken by two continent sized highlands, one in the northern and the other in the southern hemisphere. The southern continent, so to speak, is the larger, about the size of South America, whilst the northern one is about the size of Australia. Also, apart from the fact that Venus is the only major planet named for a female figure, almost all its features are named for mythical and historical female figures; for instance, the northern highland is named for Ishtar, the Babylonian goddess of love, whilst the southern one is named for her Greek counterpart, Aphrodite. The only exceptions to this rule are three features that were named before the International Astronomical Union, the body that oversees the naming of planetary features was formed in 1919. The three are Maxwell Montes, named for the Scottish mathematician and natural philosopher, James Clerk Maxwell (1831-1879) and Alpha and Beta Regio.
Perhaps the most interesting facts about Venus is that though the planet, like all other planets orbits the Sun in a counter clockwise direction, its rotation is in a clockwise direction; opposed to every other member of the solar system. Further, its rotation is the slowest of all the planets, only 6.5 kilometres per hour at the equator compared to about 1600 kilometres per hour for Earth. This slow motion means that Venus makes a complete rotation on its axis only once in 243 days! Thus, a day is longer than a year, although a hypothetical observer on the surface of the planet would actually see a new sunrise every 117 days or so, given the planet’s almost non-existent axial tilt. Finally, the planet’s orbit is the least eccentric in the solar system, more closely approximating a circle than any other.
