Venus

Saturday 31 December 2016 - 13:07:22 Posted by  Bobby

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venusrecord
 Venus is the second rocky planet from the Sun and the brightest in Earth's sky. It is Earth's inner neighbor and twin, with a similar size and mass. However, Venus has lost all of its water, and its carbon dioxide has escaped to form a very dense atmosphere that acts like a greenhouse, holding in heat.

Saskia Crater

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Impact craters on Venus vary from 168 miles down to 4 miles across. Saskia is middle-sized, at 23 miles, and has a central mountain. This radar view has been colored based on other images taken on the surface.

Cloudy World

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 Venus has a dense carbon-dioxide atmosphere and is completely shrouded by thick, highly reflective clouds made of weak sulfuric acid droplets. These start about 28 miles above the surface and extend up to a height of 43 miles. Below the clouds is an overcast, orange-colored world.

Maat Mons

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 This large shield volcano rises about 3 miles above the surrounding plains. Lava has poured out of the volcano, spread out in all directions for hundreds of miles, and then solidified.

Sister World

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 Venus is a fascinating planet. For Millennia it was known only as a bright light in the sky - third brightest, in fact, after the Sun and the Moon. Even with the advent of the telescope little more was learned about the planet, for it quickly became apparent that Venus is completely covered by clouds that prevent the surface from being seen.

 It wasn't until space probes began to make the journey to Venus in the last decades of the 20th century that we began to get an idea of what makes this planet tick. Venus is named for the Roman goddess of love, and in keeping with astronomical tradition of naming Solar System objects according to themes, almost every feature on Venus is named after women, real or mythological. The planet Venus, itself, is the only planet in the Solar System with a female name.

Morning and Evening Star Visibility

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 Being the brightest planet in the sky, Venus has naturally been known to mankind for as long as people have admired the night sky. Being an inner planet (like Mercury), however, set it apart from the known outer planets, Jupiter and Saturn, as Venus never gets very far from the Sun in the sky - it is visible for up to a few hours before dawn in the east or for up to a few hours after sunset in the west.

 This led to it being called the "morning star" and "evening star", although at first it was not realized that these two stars were the same object. It was Pythagoras who first suggested they were one and the same. Venus is so bright that, if you know exactly where to look, it can even be seen with the naked eye in the daylight sky.

 Often it will be near the Moon in the sky, making its identification easy. In fact, it is so bright that some people sometimes mistake it for a UFO - long before he became the u.s. President, Jimmy Carter once reported Venus as such!

 Venus sometimes comes between Earth and the Sun, in an event known as a transit. These come in pairs, 8 years apart, and every 243 years. The last one was in June 2004, and the next will occur in June 2012.

Odd Rotation

VenusCloudy2

 Venus has the most circular orbit of all the planets, having an eccentricity of just slightly less than 1%. (For comparison, Earth's orbit has an eccentricity of 1.7%, Jupiter has 4.8%, and Mercury a whopping 20.5%.)

 Venus orbits the Sun at an average distance of around 67 million miles, which means it is the planet that comes closest to Earth, around 25 million miles; Mars can approach to within about 35 million miles, although usually it is a lot more.

 Galileo's early observations of Venus showed it having a crescent shape at certain times in its orbit, just like the Moon. Mathematically, there was only one way this could be explained - Venus had to be in orbit around the Sun, not Earth. This revelation helped pave the way for the change from the Earth-centered view of the heavens to a Sun-centered one. Observations in the late 18th century first gave hints that Venus has a thick atmosphere. The length of the Venusian year is just under 225 Earth days, but for a long time scientists were unable to gauge the length of the Venusian day.

 For many other planets it is easy: just like through a telescope, pick a prominent feature on the planet's surface and measure the length of time it takes to go right around. But with Venus' thick cloud cover this would not work. As a planet (or any other body for that matter) rotates, one edge of it is moving toward the observer while the other edge is heading away. Scientists can measure the difference using the Doppler effect, and can use this technique to estimate a planet's rotation speed, and hence the length of its day. But when they first tried to do this with Venus it just wouldn't work. Eventually they had to conclude that the planet's rotation must be too slow to be picked up by their Doppler observations.

 Observations of the clouds in the middle of the twentieth century gave hints that Venus rotated backward compared to all the other planets.

 It wasn't until scientists turned powerful radars upon the planet, capable of penetrating the clouds and bouncing off the ground below, that they were able to accurately measure the rotation - and sure enough, it was backward, or retrograde. And the Venusian day was incredibly long - it takes a whole 243 Earth days for Venus to rotate once on its axis.

There are two main theories to account for the odd rotation. One theory is that Venus was hit by a wandering small planet at some stage of its life, stopping its normal prograde rotation, and making it turn backward. The other theory is that tidal forces acting on Venus's thick atmosphere could have operated like friction to slowly reverse the rotation.

The early radar observations showed little detail of the surface, but they could make out two broad areas that were different to their surroundings. These were named simply Alpha Regio and Beta Regio. A smaller, but more prominent, area was named Maxwell Montes, after James Clerk Maxwell, a physicist who laid the foundation for our understanding of electricity and magnetism. These three geological features are the only ones on Venus not named after female figures.

Twins

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Venus and Earth are quite alike in some ways. They are similar in size - 7,500 miles in diameter at the equator for Venus; Earth is 7,928 miles.

 Also, Venus has around 82% of Earth's mass. This, plus the fact that Venus is covered with clouds - early observers more or less assumed they were made of water, like Earth- and the fact that Venus is closer to the Sun, and hence should be warmer, led some to conclude that it was probably a jungle world. Like Earth's tropics, scientists thought Venus would have abundant plant and animal life, maybe even dinosaurs roaming the countryside. They couldn't have been more wrong.

 Venus is believed to have a very similar internal structure to that of Earth, with a core, mantle, and crust. The core is intriguing, as it is thought to be technically large enough to produce a magnetic field like Earth's, yet it seems that no such field exists. To produce such a field, the core needs to have convection currents from the hotter inner part to the outer cooler part. Venus doesn't appear to have this convection, either because the core has solidified, or else it is all at much the same temperature. The latter situation could come about because Venus is not able to get rid of its internal heat like Earth does, because the planet does not have the energy "relief valve" of plate tectonics.

 The planet does, however, have a small weak magnetic field produced by the interaction of the solar wind with the upper levels of the planet's atmosphere.

 Venus Statistics

Discovered Known from antiquity
Average distance from the Sun 67.2 million miles (108.2 million km) 0.72 AU
Equatorial diameter 7,521 miles (12,104 km)
Axial tilt 177.3°
Axial rotation period (sidereal) 243 days (retrograde)
Orbital period (in Earth days) 224.7 days
Mass (Earth=1) 0.82
Volume (Earth=1) 0.86
Surface gravity (Earth=1) 0.91
Average density (water=1) 5.24
Surface atmospheric pressure (Earth=1) 92
Escape velocity 6.4 miles/s (10.4 km/s)
Orbital eccentricity 0.007
Suface temperature (negligible variation) 867°F (464°C)
Sunlight strength 190% of Earth's (cloud tops), 5% (surface)
Albedo (reflectivity) 65%
Number of satellites 0

 Venus Timeline

Prehistory
Venus is known as the brightest object in the sky except for the Sun and the Moon.
3rd Century BCE
Venus is thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star. Venus's apparition as the morning star is also called Lucifer.
1610
Galileo Galilei is the first person to actually see Venus as more than just a bright point of light in the sky. He observed Venus through different phases.
1631
Johannes Kepler, using laborious hand calculations, predicts that Venus will pass in front of the Sun on December 6th, 1631, but the transit will not be visible from Europe.
1663
Rev. James Gregory, mathematician, suggest that a more accurate measurement of the Earth-Sun distance could be made using the transit of Venus.
1677
Sir Edmund Halley (1656 - 1742), makes the same suggestion 14 years later in 1677 and publishes a paper on the details of this technique in 1716.
1680
Halley suggests using Venus' transits to measure the Astronomical Unit (Astronomical Unit is approximately the mean distance between Earth and the Sun.)
1761
During the transit of June 5th, 1761, which was observed by over 176 scientists from more than 117 stations all over the world, the Russian astronomer make healthy. 1107 1711 - 1765, discovers a beautiful Halo of light all around Venus's dark Edge, indicating that it has an atmosphere.
1768
On August 12, 1768, His Majesty's bark Endeavor are captained by Lt. James Cook, departs England bound for Tahiti, to observe a transit of Venus on June 3, 1769.
1874
Hundreds of photographs are taken of the next transit on December 8th, 1874. This was the first use of the new technology. Few photographic plates turned out to be scientifically useful, and only a few are actually preserved for us to look at today.
1882
There is enormous public interest in the next transit on December 6th, 1882. It makes the front pages of every national and international newspaper of the time, with lavish full-length articles covering several pages.
1891
Simon Newcomb, who was in charge of the US Venus Transit Commission, publishes his best estimate of the solar parallax angle in 1891, based on all of the assembled data from several transits.
1932
Astronomers Walter Adams and Theodore Dunham use refined spectroscopic instruments to detect carbon dioxide in the atmosphere of Venus.
1961
Russian craft Sputnik 7 attempts to launch a rocket, with the Venera probe aboard, toward a landing on Venus after one Earth orbit, but ignition fails.
1962
The first spacecraft to fly by Venus is Mariner 2, back up for the Mariner 1 mission that failed shortly after launch. US astronomer, Carl Sagan calculates the effect of the atmosphere on the temperature of Venus.
1967
Mariner 5 does a flyby of Venus, revealing new information about its atmosphere, including its composition of almost 97% carbon dioxide.
1970
Venera 7 enters the atmosphere of Venus on December 15th, 1970, and a landing capsule is jettisoned. Signals are returned for 35 minutes. Then another 23 minutes of every weak signals are received after landing. The capsule is the first man-made object to return data after landing on another planet.
1978
Pioneer 13, or Pioneer - Venus 2, carries four smaller probes to be dropped into the atmosphere of Venus.
1989
The interplanetary space probe Magellan leaves Earth and falls into orbit around Venus on August 10th, 1990. It sends back spectacular radar images for a new, more-detailed map of Earth's cloud-shrouded sister planet.
2005
The European Space Agency sends Venus Express to probe the second planet. The spacecraft explores the Venusian atmosphere where scientists wish to understand the origin of violent winds that blow around the planet.

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