Often popularly known among novices as the ‘evening star’ or ‘morning star’, Venus when observed from Earth is the brightest of all the visible planets in the nighttime sky. To the Ancient Greeks, they once thought Venus was two separate celestial bodies, being the evening star Hesperus and the morning star, Phosphorus, while the early Ancient Romans thought it was both Vesper and Lucifer. Babylonians adorned this planet as the goddess of beauty and love, with the name Ishtah meaning the lovely “light-bringer.” These same ancient peoples were first to realise that both objects were the indeed same. The Greeks were soon to adopted this too, which they named after the now solitary Greek goddess, Aphrodite. Even later, the Romans named the planet Venus.

According to the Ancient writer, Gaius Julius Hyginus (c.64BC-17AD.), in the 1st century A.D. book “Astronomica” (Section II.42), who describes the mythology of the planet as:

“The fourth start is that of Venus, Lucifer by name. Some say it is Juno’s. In many tales it is recorded that it is Hesperus, too. It seems to be the largest of all stars. Some have said it represents the son of Aurora and Cephalus, who surpassed many in beauty, so that he even vied with Venus, and, as Eratosthenes says, for this reason it is called the star of Venus. It is visible both at dawn and sunset, and so properly has been called both Lucifer and Hesperus.”

Terms like “Venusian atmosphere” derive from the genitive of Venus, Veneris, but fortunately we have not used these traditional terms for planets as we do for stars and constellations. Else Venus would have to have an “Aphrodisiac atmosphere”, and certainly giving the completely wrong connotation and impression!

Of similar size to Earth, Venus is some 12,104 km. across. The planet is also closer to the Sun than us, whose almost circular orbit takes 224.7 days to complete at the mean solar distance of 0.72 A.U. (108 million kilometres). Like Mercury, Venus is a so-called inferior planet and experiences both inferior and superior conjunctions. Never drifting very far from the Sun, the maximum angle reaches only 47°. Each full cycle of lunar-like phases, over the called the synodic period, takes 1.60 years or 583.9 days, with its apparent size changing anywhere between 9.6 arcsec to 66 arcsec (or 1.1′). Venus varying geocentric distance may change anywhere between 38 and 261 million km. (M.km.), with its visual brightness accordingly varying between −4.7 and −3.5 magnitude.

Transits across the solar disk do occur, but because of the slight orbital inclination of 3.4°, they are quite rare, coming in pairs once every 127 years or so, and alternate six months apart between both in June or December. We last observed last series in December 1874 and December 1882, with the most recent ones on 8th June 2004 and 6th June 2012, both being well placed for southern Australian observers.

The NATURE of the VENUS

Venus is a totally cloud-shrouded world, whose atmosphere was discovered during a Transit of Venus by Russian born Mikhad V. Lomonosov (1711-1765) in July 1761. At first this was thought to be very similar to Earth, having the cloud cover wrongly ascribed and assumed to be water vapour. In 1932, when spectroscopy was by applied by Walter Adams (1876-1956) and Theodore Dunham Jr. (1897-1984) to the planet’s received light, revealing that the clouds were mostly composed of carbon dioxide.

Venus was once popularly considered as Earth’s twin, and quite fancifully by some imagined likely a prehistoric version of our planet. This even included primitive life-forms or dinosaurs, all living in a fern swamp. Others also considered posible intelligent creatures often imaginatively portrayed as beautiful Amazons or carefree maidens. Yet lack of real information about the nature of the atmosphere or surface remained hidden in mysteriously hidden until the 1960’s, especially when Venus was first explored by earthbound radar probe, the Mariner 2 during 1962. These old views were then quickly dispelled. It is truly a hellish world, and far from its feminine persona. Atmospheric pressure on the planetary surface is ninety-two times that of Earth, whose thick hot and corrosive atmosphere contains 96.5% carbon dioxide (CO₂) and 3.5% nitrogen (N₂). There is no oxygen. This is mixed with minute quantities of sulphur dioxide, sulphuric acid (H₂SO₄), argon, neon, carbon monoxide and very minute traces of water.

Fast upper winds move once around Venus every 4.3 days at the mean velocity of 370 km.hr^-1. This rapidly evenly spreads the oven hot 460°C surface temperature on both the dark and sunlit sides of the planet. Its generated internal heat is partly due to the proximity of the Sun, but it has become much hotter because CO₂ has trapped the sunlight via the runaway greenhouse effect. This is even more remarkable because Venus only spins in a retrograde direction once every 243.7 days and opposite to all the other Solar System planets. This remains a mystery for such differences, as a slow rotating planet should have more peaceful winds, which is still to be adequately explained. A very weak magnetic field has been found, so that core of Venus must be quite different in composition than the Earth.

PLANETARY MISSIONS

Many spacecraft have visited Venus and each have gathered a wealth of information. The first successful fly-by, after many failures by both the Americans and Russians, was NASA’s Mariner 2, passing within 34,800 km. on 14th December 1962. Next successful attempt was the atmospheric entry probe, Verena 4 (USSR), on 18th October 1967. This was followed by the close fly-by of Mariner 5 (USA), which occurred the next day on 19th October, and passed within 3990 km. of the planet. Probably the most spectacular of these early missions was Verena 7 (USSR), as it landed on the surface of on 15th December 1970. Although it landed on its side, the probe lasted just twenty-three minutes before failing from the great atmospheric pressure and temperatures, measuring the surface temperature as 475°C.

Since these early missions, there has been another nineteen successful mission encounters The most important have been the radar observations from orbit by the Pioneer Venus Orbiter (November 1978), the highly prolific American Magellan spacecraft (Aug 1990-Oct 1994), and Russian Verena 15 & 16 (Nov 1983-July 1984) found direct evidence of cratering, recently active volcanoes, plate tectonics, and several unknown geological features not seen on Earth. Russian landers, Venera 9 (22nd October 1975) and Venera 10 (25th October 1975) also obtained pictures from the surface, showing that the ambient light is similar to the sky brightness of a full moon. The most recent orbiter was the European Space Agency (ESA), Venus Express (Apr 2006-Dec 2014), which made planetary observations of the atmosphere and surface temperatures. A future mission is NASA’ Venus Multi Probe Mission (VMPM), which is being currently planned to be launched during 2022. Another is the Russian radar orbiter by Roscosmos named Venera-D, likely to be launched in 2024. Both the USA and Russia are also considering advance rovers to explore the Venusian surface perhaps during the late 2020s to 2030s.

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Last Update : 28th June 2015

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