Author: Fraser Cain

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You might be surprised to know that Venus is the hottest planet in the Solar System. With a global temperature of 735 Kelvin (462 degrees C), the surface of Venus is hot enough to melt lead. And if you could stand on the surface of Venus, you would experience atmospheric pressure 92 times greater than what you’re used to on Earth. Why is Venus so hot? The Venus greenhouse effect shows you what happens when this the process of trapping sunlight goes out of control into a runaway process.

As you probably know, carbon dioxide is a greenhouse gas. Various wavelengths can pass through this invisible gas, but it’s very effective at trapping heat. Light from the Sun strikes the ground of Venus, and warms it up. The ground tries to radiate heat back into space but the carbon dioxide traps much of it around the planet keeping it so warm. This is the same thing that happens when you keep your car windows closed on a hot day.

Scientists think that Venus used to be more similar to Earth, with lower temperatures and even liquid water on the surface of the planet. At some point, billions of years ago, the planet started to heat up. At some point, all the water on the surface evaporated into the atmosphere. Water vapor is an even more powerful greenhouse gas than carbon dioxide and this caused temperatures to rise even more. Then the surface of Venus got so hot that the carbon trapped in rocks sublimated into the atmosphere and mixed with oxygen to form even more carbon dioxide. And so today we have a carbon dioxide atmosphere on Venus which is 92 times more dense than Earth’s atmosphere at the surface.

Could this happen on Earth? Scientists think that if the same process happened on Earth, we would have temperatures with several hundred degrees C, and an atmosphere 100 times as dense as we have right now.

We have written articles on Universe Today about the Venus greenhouse effect. Here’s an article about the planet’s evolution over time, and here’s an article about how Venus could be colonized with floating cities.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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Even in ancient times, astronomers knew that Venus changed in brightness in the sky. Sometimes it’s like a dim star, and other times it becomes the brightest object in the sky (after the Moon); bright enough to cast shadows. But it wasn’t until Galileo first turned his rudimentary telescope on Venus in 1610 that astronomers first realized that Venus goes through phases, just like the Moon.

Think about the orbit of Venus for a moment. As you know, Venus orbits closer in to the Sun than Earth. One half of the planet is always in sunlight, and the other half of the planet is in shadow. It’s our view of Venus that changes. Sometimes we see Venus on one side of the Sun, and other times we see it on the other side. We can never see when Venus is completely illuminated because that’s when it’s on the opposite side of the Sun. We also can’t see when it’s completely in shadow because then it’s in between the Earth and the Sun, and the Sun obscures Venus from our view.

Just like the Moon, Venus goes through a full range of phases. When Venus has just passed out from behind the Sun, it’s almost a full circle, but it’s dim because it’s nearly at its most distant point from Earth. Then it “catches up” to Earth’s orbit as it travels around the Sun. Venus becomes brighter and brighter but also does into a half phase and eventually a slim crescent. You might be surprised to know that Venus is at its brightest when it’s a slender crescent.

The only way to see the phases of Venus is through a telescope. So find a friend with a telescope, ask them when Venus is going to be bright in the sky, and ask them for a chance to take a look.

We have written many articles on Universe Today about observing Venus. Here’s one article about a time when Venus, the Moon and Jupiter were all visible in the sky at the same time, and here’s one about Venus and Jupiter.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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One of the nicknames of Venus is “the Morning Star”. It’s also known as the Evening Star. Of course, Venus isn’t a star at all, but a planet. So why does Venus have these nicknames?

The orbit of Venus is inside the orbit of Earth. Unlike the outer planets, Venus is always relatively close to the Sun in the sky. When Venus is on one side of the Sun, it’s trailing the Sun in the sky and brightens into view shortly after the Sun sets, when the sky is dark enough for it to be visible. When Venus is at its brightest, it becomes visible just minutes after the Sun goes down. This is when Venus is seen as the Evening Star.

When Venus is on the other side of the Sun, it leads the Sun as it travels across the sky. Venus will rise in the morning a few hours before the Sun. Then as the Sun rises, the sky brightens and Venus fades away in the daytime sky. This is Venus the Morning Star.

The ancient Greeks and Egyptians thought that Venus was actually two separate objects, a morning star and an evening star. The Greeks called the morning star Phosphoros, “the bringer of light”; and they called the evening star Hesperos, “the star of the evening”. A few hundred years later, the Hellenistic Greeks realized that Venus was actually a single object.

We have done several articles on Universe Today encouraging readers to go out and see Venus the Morning Star. And here’s what Venus looks like in a telescope.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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Venus is one of the planets visible with the unaided eye. Because it has always been easy to see, it’s impossible to say who discovered Venus. In fact, after the Moon and the Sun, Venus is the brightest object in the sky – it’s likely ancient people thousands of years ago knew about it.

You can’t really talk about the discovery of Venus, but historians do know when observations of Venus were first written down. In fact, one of the oldest surviving astronomical documents is a Babylonian text that talks about Venus in 1600 BC. It contains a 21-year record of Venus’ appearances. Venus played a part in the mythology of many ancient peoples, including the Mayans and the Greeks.

The first person to point a telescope at Venus was Galileo Galilei in 1610. Even with his crude telescope, Galileo realized that Venus goes through phases like the Moon. These observations helped support the Copernican view that the planets orbited the Sun, and not the Earth as previously believed.

Astronomers predicted that Venus would transit across the surface of the Sun. The first time this was observed was on December 4, 1639, and later transits helped astronomers discover that Venus has an atmosphere, and helped calculate the distance from the Earth to the Sun with great accuracy. The last transit of Venus happened in 2004, and the next one will happen in 2012.

Although the surface of Venus is obscured by thick clouds, radar signals were bounced of the surface of the planet in 1961. This allowed astronomers to calculate its radius accurately, and measure its speed of rotation. They also discovered that its axis of rotation is almost zero.

The first spacecraft to actually visit Venus was NASA’s Mariner 2, which flew past Venus in 1962. More recently, NASA’s Magellan spacecraft visited Venus and extensively mapped it surface with radar. ESA’s Venus Express arrived at Venus in May, 2006.

You might be surprised to know that Russian spacecraft have actually landed on the surface of Venus. Although there were several failed attempts, the first spacecraft to actually land on the surface of Venus and survive was Venera 7; although, it was only able to transmit for about 35 minutes.

So, it’s hard to say who actually discovered Venus. The first caveman who stepped outside in the early evening would have noticed bright Venus. But since the discovery of the telescope, and the beginning of the space age, scientists have really been able to discover Venus.

Here are articles about two planets in the Solar System that were actually discovered in recent times. Here’s an article about the discovery of Uranus, and here’s an article about the discovery of Neptune.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

References:
NASA: Transit of Venus
NASA Solar System Exploration: Venus

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The volume of Venus is 9.38 x 10¹¹ km³.

That sounds like a big number, and it is. Here’s the long version: 938,000,000,000 cubic kilometers. Just for comparison, the volume of Venus is 86% the volume of the Earth. That’s why many scientists consider Venus to be the twin planet to Earth. Of course, when you consider that the temperature on the surface of Venus is hot enough to melt lead, and atmospheric pressure is 92 times what you would experience on Earth, and Venus doesn’t exactly seem like Earth’s twin.

Of course, the volume of Venus is just a tiny fraction of the volume of the Sun. You could fit 1.5 million planets the size of Venus inside the Sun and still have room to spare.

It’s hard to study the interior of Venus, but scientists think that the volume of Venus is very similar to the volume of the Earth. The planet has a core of liquid metal surrounded by a mantle of molten rock. This is covered by a crust of solid rock.

Want to know about other objects in the Solar System? Here’s the volume of the Moon, and the size of the Sun.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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The radius of Venus is 6,052 km. Double that and you get the diameter of Venus: 12,104 km.

Need some comparison? The equatorial radius of Earth is 6,378 km, so the radius of Venus is 95% the Earth’s radius. With such a similar size, you can see why Venus is considered Earth’s twin planet (evil twin, really, when you consider it’s hot enough at the surface to melt lead, with an atmosphere 92 times as thick as Earth).

With other planets in the Solar System, we talk about their equatorial and polar radii. That’s because most planets are rotating on their axis so quickly they’re a little flattened out, with a bulge around the equator. For example, here on Earth, points at the equator are actually 7 km further from the center of the Earth than the poles.

Venus, on the other hand rotates so slowly on its axis that it isn’t flattened out at all. While Earth takes 24 hours to complete one rotation, Venus takes 243 days to spin once on its axis (it also rotates backwards compared to the other planets in the Solar System, but that’s another story).

So the radius of Venus is 6,052 km, whether you calculate it from the center to the equator, or the center to the poles.

Want to know the radius of other planets? Here’s an article about the radius of Mercury, and here’s an article about the radius of the Moon.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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Although it’s similar in size, Venus is very different from Earth. The temperature at the surface is hot enough to melt lead, with an atmosphere of almost pure carbon dioxide, 92 times thicker than Earth’s atmosphere. Even with this extreme environment, is it possible that there’s life on Venus?

Probably not.

Here on Earth, we find life wherever we find liquid water: kilometers deep underground, beneath glaciers, and even inside nuclear reactors. If there’s liquid water, there’s life. But there doesn’t seem to be any liquid water on Venus.

Scientists think that Venus did have liquid water billions of years ago, but a runaway greenhouse effect heated up the planet to the point that all the water evaporated, and was eventually lost to space. The atmosphere is now 96% carbon dioxide, with the rest nitrogen and a few other trace compounds.

But there’s another possibility. High up in the atmosphere of Venus, at an altitude of 50 km, the air pressure and temperature get to the point that they’re very similar to Earth. In fact, at this altitude, it’s the most Earthlike place in the whole Solar System. Some scientists think that there could be microbial life high up in the atmosphere of Venus.

Since the Sun’s solar wind is constantly blowing on Venus, and Earth is “downwind” from Venus, it’s possible that microbial life is being blown from Venus to Earth. Maybe life on Earth got its start on Venus.

You can read a longer article about the possibility of life on Venus here. And here’s a video that shows how the atmospheres of Venus and Mars leak into space.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.