Since Venus is one among the few planets visible to the naked eye, it can be assumed that a group of humans discovered it during the ancient times. About 15 centuries earlier, Greek astronomer, Ptolemy is said to have discovered it. His model of the solar system claimed that all celestial objects revolve around the Earth. The model of the solar system developed by Copernicus that placed the Sun at the centre recognized both Venus and Earth to be planets. Further in 1610, Galileo confirmed the theory of Copernicus as he pointed out his telescope at Venus showing that Venus went through distinct phases, similar to the Moon. However, when Venus made a transit across the surface of the Sun on 4th December 1639, the legitimacy of this model was substantiated even further.
Being very close to the Earth, Venus appears as the brightest and biggest star at night. It is the second planet from the Sun, that is, about 67 million miles from the Sun. With a mass of about 4.8676x1024 kg, it rotates slowly on its axis and takes about 243 earth days to complete one rotation. However, its orbit period of 225 days earth days makes a year on Venus shorter on day. With an equatorial diameter of 12,104 km, Venus, like Uranus, rotates clockwise on its axis. Venus, like earth has no moons. In comparison with the Earth’s orbit, the orbit of Venus being nearer to the Sun, it appears in roughly the same spot every time. It is visible only around the time of sunrise and sunset.
Venus has a hellish atmosphere which includes poisonous gases like carbon dioxide. This traps a lot of heat further increasing the temperatures on Venus. The temperature on the planet is about 465°C, hot enough to melt lead. Also, around this atmosphere is a cloud layer of sulphuric acid and it is suspected that Venus has acid rains which become another factor to eliminate the possibility of life on it. In addition to this, unlike the Earth, it does not have the protective layer of Ozone that shields life from the ultraviolet rays of the Sun. These harmful radiations reach the surface of Venus and break water molecules into Hydrogen and Oxygen. So, it is a dry planet and cannot support life. Earth-based observatories and Venus-orbiting spacecraft have provided global-scale information on the nature of the planet’s surface. All have used radar systems to penetrate the dense Venusian clouds. Most of the surface is rocky, dry and plain. However, some features like mountains and ranges exist and can be attributed to tectonic activity (deformational activity in the crust). Two striking ones are the Ishtar terra in the northern hemisphere and Aphrodite terra near the equator. Ishtar terra has the most spectacular topography on Venus. It contains a plateau called Lakshmi Planum resembling in configuration the Plateau of Tibet on Earth. Another mountain range Maxwell Montes resembles the Himalayas. Thus, the crust is about 20–50km thick.
Less is known about the core. But scientists presume it to be metallic – primarily iron and nickel, similar to the composition of that of the Earth. However, in case of Venus, it is the mantle – the layer between the core and the crust that makes up bulk of the planet.
Venus is covered with a dense cloud and a dense atmosphere. Telescopic views show a peaceful yellow ball revealing little else. Therefore, missions have been sent. Early and succesful Venus missions undertaken by the United States involved Mariner 2, Mariner 5 (1967), and Mariner 10 (1974). Each spacecraft made a single close flyby, providing successively improved scientific data in accord with concurrent advances. The first spacecraft sent by the Soviet Union in the 1970s sent probes on the surface of Venus but these lasted only a few hours before being burnt down on account of high temperatures there. In 1978, the United States launched the Pioneer Venus mission, comprising two complementary spacecraft. The Orbiter went in to orbit around the planet, while Multiprobe released four probes that were targeted to widely separated points in the Venusian atmosphere to collect data on atmospheric structure and composition. Pioneer Venus Orbiter was one of the long-lived planetary spacecraft, returning data for more than 14 years.
Ancient civilizations believed that Venus was two distinct stars that appear in the sky. It changes from being visible at sunrise to being visible at sunset when the orbit of Venus overtakes Earth’s orbit. Hence, it was called the Morning Star and the Evening Star. The Greeks knew it as Phosphorus and Hesperus whereas the Romans called it Lucifer and Vesper.