Conjuction of Moon, Venus & Jupiter (w/moons). Photo courtesy of Tavi Greiner
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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.
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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.
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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.
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The size of a planet is measured in many ways: mass, volume, equatorial diameter, and surface area are the most common. In this article we are going to explore each of these ways to express the size of Venus and a few interesting facts about our close neighbor.
Venus has a diameter that is about 95% of Earth’s. It is 12,100 km across. The Venusian surface area is around 90% of our own at 4.6×108 km2. The planet has a volume of 9.38×1011 km3. That puts it a little over 85% of Earth’s volume. One final way to measure the size of Venus is to consider its mass. It has a mass of 4.868 x 1024 kg., just over 81% of Earth’s. These physical characteristics have led many scientists to call Venus the sister planet of Earth.
Size characteristics are the only things that Earth and Venus have in common. At 462°C, Venus has an average temperature that is 410°C higher than the hottest deserts on Earth. The temperature on the Venusian surface can melt lead. You have to be 50 km from the surface to find temperatures that are anything like here on Earth.
Temperature is not the only extreme on Venus. The atmosphere would prevent any life as we know from surviving. To start with, the atmospheric pressure is 92 times that of Earth. It is choked with volcanic ash, sulfuric acid clouds, and is made of 95% carbon dioxide. There are constant hurricane force winds churning the atmosphere. Sustained winds in excess of 360 kph are always present. The conditions on the planet are so extreme that probes can only last a few hours.
The surface shows over 1000 volcanoes or volcanic remnants that are over 20 km in diameter. There are no small impact crater, because the atmosphere is too thick to allow small objects to penetrate to the surface. Scientists believe that the entire surface of the planet was been replaced by volcanic activity 300 to 500 million years ago.
Venus has been visited by spacecraft several times. NASA sent Mariner 2 in 1962. It was the first spacecraft to send information from another planet. The Soviet space program landed Venera 7 in 1970. It was the first spacecraft to land on another planet. NASA’s Magellan mapped 98% of the surface in the early 1990s and the European Space Agency currently has the Venus Express in orbit studying the planet’s atmosphere. In all, we have gained a great deal of information about this inhospitable planet in the last 30 years.
Want to know the size of other planets in the Solar System. Here’s an article about the size of Jupiter, and here’s an article about the size of Saturn.
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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.
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The mass of Venus is 4.868×1024 kg. That is about 82% of the mass of Earth. Alright, end of story and thank you for reading. Okay, we would never do that to you here at Universe Today. There are far too many interesting facts about Venus to leave you hanging like that.
Here are a few other physical characteristics of the second rock from the Sun:
Diameter
12,100 km
Surface Gravity
8.87m/s2
Surface Area
460,000,000 km2
Volume
9.38×1011km3
Surface Atmospheric Pressure
92 times that of Earth
Average Surface Temperature
462 degrees Celsius
Rotation
Retrograde
Density
5.204 g/cm3
Scientists believe that the high mass and density of Venus can be accounted for by its high concentration of rock and metals. They believe that the planet has a liquid metallic core that is surrounded by a molten rock mantle. Actual proof of this is nearly impossible since the reflective nature of the planet’s atmosphere makes many types of observation impossible.
Venus was once thought to be a dead planet. There is no life on the surface for many reasons, but recent study of the surface has revealed that there may be active volcanoes on the planet. That means that it is alive, geologically speaking. Previously, scientists had known that the planet had been resurfaced by volcanic activity 300 to 500 million years ago, but had thought that the activity died out during that same time frame.
There have been many missions sent to Venus. The Soviet space program started the race to Venus with the Venera program. It is hard to tell exactly how many Soviet missions to Venus were launched since the program would not announce a probe that failed, but more than a dozen were successful. NASA launched several mission of its own. Early missions from both programs failed because neither was prepared for the extreme pressure within the Venusian atmosphere. Even those that were able to transmit from the surface could only survive for less than one hour.
The Venus Express is currently in orbit around Venus. BepiColumbo is set to launch in 2014. It is hoped that the Akatsuki probe can reawakened to gather information when it arrives in the area in 2016 and the Venus In-Situ Explorer is in the planning stages. Scientists are determined to unravel the planet’s mysteries. Like you, they want to know more than the mass of Venus.
Image constructed from Venus Express data - atmospheric particles being stripped away by the Solar Wind (credit: ESA)
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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.
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When you look at the Moon and Mercury, their surfaces are pounded with impact craters. Mars has many craters, and even Earth has its share. But what about Venus, are there craters on Venus?
There are craters on Venus, but not many. The Solar System is relatively empty now, but less than a billion years after the formation of the Solar System, there were still many objects left over. These crashed into planets and moon, during a time scientists call the late period of heavy bombardment. Many of the craters on Mercury and the Moon were formed during that time.
Strangely, Venus shows no record of the heavy bombardment period. Either it didn’t get struck, which is unlikely, or some process resurfaced the planet, removing all traces of the impact craters. The resurfacing process stopped at some time in Venus’ more recent history. And so, all the craters that scientists do see on the surface of Venus are relatively young.
Craters on Venus are different from craters on other planets. The planet’s thick atmosphere stops the smaller objects from even reaching the surface of Venus; they just burn up in the atmosphere. There are about 1000 craters identified on the surface of Venus.
Crater Mead is the largest known crater on Venus, named after the American anthropologist, Margaret Mead. It measures 280 km in diameter, and contains several concentric rings.
We have written many articles about Venus on Universe Today. Here’s an article about the evolution of Venus’ surface, and here’s a “Where in the Universe” challenge featuring a crater on Venus.
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Like all the planets, Venus formed approximately 4.6 billion years ago when the Sun and the Solar System came out of the solar nebula. So, the age of Venus is 4.6 billion years old.
Before the Solar System, there was just a large cloud of hydrogen gas in a giant nebula. Some event, like a nearby supernova explosion put a shock into the cloud, and caused it to begin collapsing. Many stars, large and small, formed in this nebula, and one of these went on to be the Sun. As the material condensed together, conservation of momentum caused it to spin up and flatten out.
A protoplanetary disk of material formed around the newborn Sun, and it was here that the planets formed. Dust clumped together to form rocks, rocks smashed together into boulders, and mountain-sized objects became protoplanets. In the first few hundred million years of the age of Venus, it’s likely that the planet was smashed many times by these large asteroid and protoplanets. But eventually, Venus became the dominant object in the region, sucking in everything with its gravity.
We know that Venus was probably the victim of a large collision because it rotates in the opposite direction from the rest of the planets in the Solar System. A large collision could have turned its rotation backwards.
How do we know Venus’ age? We can’t measure the age of Venus directly, because of the intense heat and pressure on the surface of Venus. Instead, scientists measure the age of meteorites that have fallen to Earth. After analyzing hundreds of objects, scientists have found that they all formed at approximately the same time. These meteorites are the leftover pieces from the formation of the Solar System, and help prove that all the objects in the Solar System formed at the same time.
And so we know that the age of Venus is 4.6 billion years old.
We have written many articles about Venus. Here’s one about how life on Venus could be blown to Earth, and here’s an article about how you might keep a Venus rover cool.
If you love a cosmic mystery – and which one of us doesn’t – then you’re going to really enjoy what’s about to occur in the night sky. It all has to do with an easily located variable star in the constellation of Cepheus and an unseen companion which crosses its path every 5.6 years…
Click to enlarge mapThe star’s name is EE Cephei (RA 22 09 22.76 Dec +55 45 24.2) and and 10.8 magnitude it’s well within range of large binoculars and small telescopes. You’ll find it located about a degree and a half southwest of 4.2-magnitude Epsilon Cephei (about a finger width held at arm’s length). This will get you in the correct approximate field. For smaller optics you’ll see far fewer stars than what are depicted on the photographic chart, but the brighter ones will lead the way. However, in larger telescopes you’ll easy pick out the star patterns – so use the inset to help guide you to the right star! Now, here’s why it’s so important…
According to Mike Simonsen’s excellent blog: “This story starts in the 1950’s with the discovery of the variable nature of the star EE Cephei (Cep). Astronomers noticed it fainter than normal in 1947 and again in 1952. At first it was suspected of being an R Coronae Borealis type star. These are giant Carbon-rich, Hydrogen-poor stars that exhibit unpredictable fading episodes, believed to be caused by dust forming episodes in the outer layers of these stars’ atmospheres. The dust blocks the visible light, so we see the star fade, sometimes dramatically, by up to 9 magnitudes. It can take a year or more for them to return to maximum light, where they will shine contentedly for another undetermined period before coughing up dust and fading again.
When EE Cep faded again in 1958, Italian astronomers Romano and Perissinnotto suggested it might actually be an eclipsing binary with a very long period. Eclipsing binaries are stars that orbit around a common center of mass, and due to a line of sight effect we see them fade at regular intervals as one star passes in front of the other from our point of view. Sometimes, the alignment is so nearly edge on that we see a secondary eclipse as the smaller star of the binary pair disappears behind the primary. Because the orbits of these binaries are usually quite stable and the eclipses occur at regular intervals, observing eclipsing binaries is extremely helpful to astronomers in determining stellar masses, sizes, temperatures, luminosities and orbital parameters. Most have periods measured in hours, days or weeks because they are compact systems, with the stars in close proximity to each other, if not actually in contact.”
Exciting? Maybe not to some, but to those of us who not only enjoy astronomy as a passtime, but as a vocation – any event is welcomed and thoroughly studied. The EE Cephei event was confirmed after eclipses were observed again in 1964 and 1969 by L. Meinunger published the first ephemeris and established a period of 2049 days. All of this was well and good – but no secondary eclipse has ever been observed.
Says Mike: “The mysteries about this star were far from being unraveled though. One of the striking characteristics of EE Cep is the different eclipse depths and durations. Unlike many eclipses, whose periods can be measured to 8 significant digits, and whose range in magnitudes is very predictable, all of the observed eclipses of EE Cep have been different from each other in depth and duration.”
What’s happening is something strange is occurring with the light curve – it’s bottoming out and there may be a very good reason. As a highly respected member of the American Association of Variable Star Observers (AAVSO), Mike Simonsen has an answer to that mystery, too. “The most popular model to explain the secondary is that of a dark, opaque, relatively thick disk around a low-mass single star or a close binary. Differences in the shape of the particular eclipses could be explained by changes in both the inclination of the disc to the line of sight, and the tilt of its cross-section to the direction of motion.
The majority of the eclipses exhibit five repeatable phases that can be explained if the secondary is a disk shaped object with a gap in the center, like a giant cosmic donut. First, atmospheric and real ingress, where the dusty disk begins to obscure the light from the primary star, and then obscures it more fully as thicker, more opaque material blocks the light from the primary. Then a sloped-bottom transit, as the primary shines through the hole in the donut as it passes in front of the star. Then finally, real and atmospheric egress, as the disc moves away from in front of the primary star. The unique, flat-bottomed eclipse observed in 1969, can be explained by a nearly edge-on, non-tilted eclipse of the primary by the disc.
The color filter observations from the last eclipse show two increases in blue light (blue maxima) about 9 days before and after mid-eclipse. These subtle increases can be explained by the primary being a rapidly rotating Be star. These stars are darker around the equator and bluer at the poles. The reason there are two blue maxima can be explained if the disc is divided into two parts by a transparent gap. Spectroscopic observations show that the eclipsed component is a rapidly rotating Be star.”
Does this answer all the questions about EE Cephei? No. That’s the purpose of this article… More observations are needed and so is the help of all amateur astronomers ready and willing to take on the task. According to Mike, “The issue is far from settled. The light and color variations may have more to do with the different opacities in different parts of the disk. And here is where you can help write the story of this mysterious object. The next eclipse of EE Cephei starts right now. Mid-eclipse is predicted for January 14-15, 2009. The critical time to catch the blue maximums will fall between January 2nd and 27th. The longest eclipse lasted 60 days, so early December is the time to start taking data on this star, and observations should continue through the end of February.
If you have a CCD equipped with one or more science filters (UBVRI), astronomers at AAVSO will be very anxious to have you submit your data. If you are a visual observer, you can submit data on this eclipse also. EE Cep is normally a 10.8 magnitude star, and fades to anywhere from 11.5 to 12.5V. Thus it is easily observed with a telescope of 4” or more. Comparison charts for this star can be downloaded from the AAVSO’s Variable Star Plotter (VSP). There is a handy one page instruction for using VSP linked right from the top of that page.”
So, what are you waiting for? Here’s your chance to practice some serious astronomy!
