Qendra Shqiptare e Astrofizikes

Atmosphere

About

Venus is the second planet from the Sun and the sixth largest it is known as the jewel of the sky. It is the sixth largest planet and has an orbit more circular than any other planet.

The planet, being so close to the Earth is one of the brightest objects in the sky (besides the Sun and the Moon) and has been observed all the way to prehistoric times. At one point in its history, Venus was thought to be two separate bodies, Eosphorus (the morning star) and Hesperus (the evening star). It is named after the goddess of love and beauty probably because it is the brightest planet seen in the ancient times. It is the only planet without a moon.

Venus spins so slowly that one day on the planet lasts 8 months on Earth. Once every 243 Earth days, Venus rotates.  However, it rotates in the opposite direction to most of the other planets. The same side of Venus faces the Earth every time their orbits pass each other.

Venus is the planet that comes closest to the Earth; it comes as close as 25.7 million miles (41.4 million km) from our planet.

Historically, Venus has been evidence toward Copernicus's heliocentric theory due to its visible phases when observed from Earth. The discovery ofthe Galilean moons of Jupiter was also a favorable discovery toward the theory. However, Galileo was jailed for his findings due to the strong belief in the geocentric theory.

Venus has no magnetic field, perhaps because of its slow rotation. Venus orbit is the most nearly circular of that of any planet.

Venus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named probably because it is the brightest of the planets known to the ancients. (With a few exceptions, the surface features on Venus are named for female figures).

Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better.

Since Venus is an inferior planet, it shows phases when viewed with a telescope from the perspective of Earth. Galileo's observation of this phenomenon was important evidence in favor of Copernicus's heliocentric theory of the solar system.

The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on another planet, and Venera 9 which returned the first photographs of the surface. Most recently, the orbiting US spacecraft Magellan produced detailed maps of Venus surface using radar.

Venus rotation is somewhat unusual in that it is both very slow (243 Earth days per Venus day, slightly longer than Venus year) and retrograde. In addition, the periods of Venus rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known.

Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar:

-- Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).
-- Both have few craters indicating relatively young surfaces.
-- Their densities and chemical compositions are similar.

Because of these similarities, it was thought that below its dense clouds Venus might be very Earthlike and might even have life. But, unfortunately, more detailed study of Venus reveals that in many important ways it is radically different from Earth.

There isn't any life on Venus, although it is similar to Earth in many ways.  This is because it is too hot, too dry, and too poisonous.  Venus atmosphere is mostly made of carbon dioxide, with sulfuric acid, which is a deadly poison, in its upper clouds. The planet's distance from the sun and its atmosphere are the reasons it's so hot.  Because of a process known as the "greenhouse effect" the carbon dioxide absorbs and traps the Sun's heat that reaches the surface.  Therefore, the heat is not released back into space.  Venus is the hottest planet. Venus surface temperature by about 400 degrees to over 740 K, that's hotter than a kitchen oven.  In fact, Venus surface is hot enough to melt lead and the planet's rocks can glow because they are so hot. The pressure of Venus atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans).

Many scientists argue that Venus was subjected to a so-called runaway "greenhouse effect." They say this effect caused any oceans to evaporate into the atmosphere. Unless carbon emissions are reduced on our planet, the same fate may await Earth.

There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises. Venus surface is actually hotter than Mercury's despite being nearly twice as far from the Sun.

There are strong (350 kph) winds at the cloud tops but winds at the surface are very slow, no more than a few kilometers per hour.

Venus probably once had large amounts of water like Earth but it all boiled away. Venus is now quite dry. Earth would have suffered the same fate had it been just a little closer to the Sun. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.

Most of Venus surface consists of gently rolling plains with little relief. There are also several broad depressions: Atalanta Planitia, Guinevere Planitia, Lavinia Planitia. There two large highland areas: Ishtar Terra in the northern hemisphere (about the size of Australia) and Aphrodite Terra along the equator (about the size of South America). The interior of Ishtar consists mainly of a high plateau, Lakshmi Planum, which is surrounded by the highest mountains on Venus including the enormous Maxwell Montes.

Data from Magellan's imaging radar shows that much of the surface of Venus is covered by lava flows. There are several large shield volcanoes (similar to Hawaii or Olympus Mons) such as Sif Mons (right). Recently announced findings indicate that Venus is still volcanically active, but only in a few hot spots; for the most part it has been geologically rather quiet for the past few hundred million years.

The oldest terrains on Venus seem to be about 800 million years old. Extensive volcanism at that time wiped out the earlier surface including any large craters from early in Venus history.

Magellan's images show a wide variety of interesting and unique features including pancake volcanoes which seem to be eruptions of very thick lava and coronae which seem to be collapsed domes over large magma chambers.

The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km in radius, a molten rocky mantle comprising the majority of the planet. Recent results from the Magellan gravity data indicate that Venus crust is stronger and thicker than had previously been assumed. Like Earth, convection in the mantle produces stress on the surface which is relieved in many relatively small regions instead of being concentrated at plate boundaries as is the case on Earth.

Venus is usually visible with the unaided eye. Sometimes (inaccurately) referred to as the "morning star" or the "evening star", it is by far the brightest "star" in the sky. There are several Web sites that show the current position of Venus (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program such as Starry Night.

Even though it's hot on the surface, Venus days aren't filled with sunlight, its dense clouds only allow about 15 % of the Sun's light to pass through. However, the planet's nights aren't totally dark either because the clouds bend light so it hits its night side. The clouds also cause high surface pressure.

Although Venus atmosphere does not allow for life, its bright yellow clouds look appealing from space.  In fact, the planet was so attractive that it was named after the Roman goddess of love and beauty.  Venus is the only planet, that when it is near its brightest point, can be seen in daylight; besides the Moon and Sun, it is the brightest object in the sky.  At night, it shines more brightly than any other planet or star in the sky.  Venus has been called the "evening star" because it looks like the first star of the night.  At certain times of the year, the planet can be seen in the east at sunrise.  At other times, it can be seen in the west at sunset.  Ancient astronomers thought they were seeing two different objects in the sky.  They called Venus "Phosphorus" or "Lucifer" when it appeared at sunrise and "Hesperus" when it appeared at sunset.

NASA has sent several space probes to Venus, including Mariner 2 in 1962, Mariner 5 in 1967, and Mariner 10 in 1974.  Pioneer Venus and Pioneer Venus 2 were spacecraft sent to the planet. The U.S. Magellan mapped 98 % of the planet during the first half of the 1990s.

Venus has been shown to have an environment that is probably the most hostile in the entire Solar System. The surface temperature is about 737 K, the atmosphere is mainly carbon dioxide, and the clouds contain sulphuric acid.  At low levels, thunder and lightning is continuous and the pressure of the atmosphere is at least 90 times that of the Earth's air.  Information from the Russian Venera soft-landers indicates that the level of light on the surface is greater than had been expected: it has benn compared with that in Moscow on a cloudy winter day.  By 1981 it had been established that Venus has a vast rolling plain, together with two highland areas (Ishtar and Aphrodite), high peaks, and craters. The most recent probe, Magellan, orbited the planet for 3 years taking highly detailed radar maps of the surface and returning images as clear as any photographs. One area, Beta Regio, contains two huge volcanoes which are probably active.

There are no small craters on Venus. It seems that small meteoroids burn up in Venus dense atmosphere before reaching the surface. Craters on Venus seem to come in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.

The surface on Venus is literally a storybook of its very diverse and interesting history. It is scattered with a variety of craters created from multiple asteroids and meteorites. Due to the thick atmosphere, it is unusual to find any small craters two kilometers (1.2 miles) or less on the surface because they usually burn up and or disintegrate into much smaller pieces. Sometimes larger meteorites break up into smaller pieces before impact and create crater clusters.

In addition the surface is also heavy with Venusian volcanoes of all shapes and sizes. At least 85% of Venuss surface is composed of volcanoes and volcanic rock. The history of Venuss heavy terrain dates back almost 800 million years when the planet violently reformed its surface due to heavy volcanism that wiped out any previous craters. Now Venus has over 100,000 small shield volcanoes with hundreds of large volcanoes. Lava flows from the volcanoes carved long canals that extend up to 7,000 kilometers (4,300 miles).