Posted on by Fraser Cain

Black Hole Pictures

Magnetic field around a black hole. Image credit: NASA

Want to see some black hole pictures? Here’s a challenge, how to show an image of something that absorbs all the light that reaches it. Of course, it’s impossible to show any real pictures of black holes because they’re invisible. But you can show the regions around black holes as well as illustrations of what black holes might look like.

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This black hole picture shows the invisible black hole at the center surrounded by an accretion disk of material. The rapid rotation of the black hole interacts with the accretion disk generating powerful magnetic fields.

Artist's illustration of a supermassive black hole. Image credit: NASA
Artist's illustration of a supermassive black hole. Image credit: NASA

This is a picture of a supermassive black hole (artist illustration). You’re seeing the black hole from the side, and it’s surrounded by a thick torus of gas and dust that obscures the region around the black hole from view. The powerful magnetic fields of the black hole generate powerful jets that stream out into space.

Supermassive black hole suppressing star formation. Image credit: NASA
Supermassive black hole suppressing star formation. Image credit: NASA

This artist photo of a black hole shows a supermassive black hole at the center of a galaxy. Powerful radiation is streaming out of the black hole’s core, stopping star formation in regions close to the center of the galaxy.

Evidence for a spinning black hole. Image credit: NASA
Evidence for a spinning black hole. Image credit: NASA

This black hole picture shows a black hole spinning rapidly at the center of its accretion disk. Although the black hole itself is invisible, it’s surrounded by a fast disk of material falling into the black hole, like water going down a drain.

Black hole binary. Image credit: NASA
Black hole binary. Image credit: NASA

Here’s a black hole picture that shows a black hole in a binary relationship with a star. Material is streaming off of the star, and into an accretion disk around the black hole. The rapidly rotating black hole generates a powerful magnetic field that creates twin jets of material streaming above and below the black hole.

Posted on by Fraser Cain

Who Discovered Venus?

Venus captured by Magellan.

Venus is easy to see with the unaided eye. In fact, it’s the brightest object in the night sky after the Moon, so it’s safe to say that humans have been aware of Venus since people have looked to the skies. In fact, there are 5 planets visible with the unaided eye: Mercury, Venus, Mars, Jupiter and Saturn. It’s actually impossible to say who discovered Venus, since the planet has been known since before recorded history. Humans have been on Earth for 200,000 years, so maybe that’s how long we’ve known about the planet.

But ancient astronomers didn’t really know what Venus was. They knew it was an object that moved in the sky from night to night, sometimes being obscured by the glare of the Sun. But it wasn’t until Copernicus developed his model of the Solar System that placed the Sun at the center, and the planets orbiting it. At that point, both Venus and Earth were recognized to be planets.

Galileo pointed his telescope at Venus in 1610, and confirmed Copernicus’ theory by showing that Venus went through distinct phases, just like the Moon. The phases matched the predictions made by Copernicus, and demonstrated that Venus was really a planet, orbiting the Sun and not the Earth.

This model was confirmed even more when Venus made a transit across the surface of the Sun on December 4, 1639. The most recent transit of Venus happened in 2004, and the next one will occur in 2012.

Even in the best telescopes we have today, the surface of Venus is obscured by thick clouds, so it’s impossible to see any features on its surface. It wasn’t until radar signals were bounced off Venus in 1961 that scientists had any way to calculate the planet’s speed of rotation and axial tilt.

The first spacecraft to visit Venus was Mariner 2, but more recent spacecraft, like NASA’s Magellan were equipped with radar instruments that can peer through the thick atmosphere of Venus and reveal the hellish surface below.

Spacecraft have even landed on the surface of Venus. The Russian Venera program put a handful of landers on the surface of Venus, which were able to send home images of the surface before they malfunctioned in the incredible heat and pressure found on the surface of the planet.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

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

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

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

Posted on by Fraser Cain

How Many Rings Does Saturn Have?

Saturn's Rings. Image credit: NASA/JPL/SSI

Saturn is best known for its elaborate ring system. They’re made of icy particles orbiting the planet. The rings have distinct divisions, and astronomers have separate designations for each of Saturn’s rings. But how many rings does Saturn have?

The question is actually impossible to answer. Saturn has more than a dozen rings and gaps within the rings – and more are being discovered by spacecraft like NASA’s Cassini. But the planet does have several major ring systems and gaps within them.

The two densest parts of the rings are the A and B rings, separated by the Cassini Division, and then the C Ring. So, is that 3 rings, or 4? Whatever the case, these comprise Saturn’s main rings.

After the 3 main rings, you have the smaller, dusty rings: the D Ring, G Ring, E Ring, and others beyond that. There’s also the F Ring, which is just outside the A Ring.

That’s 3 main rings and 5 dusty rings for a total of 8 rings, 9 if you count the Cassini Division.

But there are even more rings around Saturn. There’s the Janus Ring, the Methone Ring Arc, the Anthe Ring Arc and the Pallene Ring, as well as the Roche Division. 4 more rings and another division.

That brings us to 12 rings and 2 divisions.

But then there are also smaller divisions and gaps within the various rings that would bring the total to more than 30 (the Encke Gap, the Huygens Gap, the Dawes Gap, and many more).

To answer the question, how many rings does Saturn have, you really need to find out how closely you’re looking. From what you might be able to see, there are 3 rings. With powerful telescopes, you can make out 8 rings. And with spacecraft like Cassini orbiting Saturn, that total rises above 30.

We have written many articles about Saturn’s rings for Universe Today. Here’s an article about a time when Saturn’s rings were disappearing, and here’s an article about vertical structures that tower above Saturn’s rings.

Here’s the same question answered by Ask an Astronomer. Here’s an easier question, how many moons does Saturn have?

We have done an entire episode of Astronomy Cast all about Saturn. Give it a listen.

Reference:
NASA

Posted on by Fraser Cain

What is the Ozone Layer?

Ozone layer hole. Image credit: NASA
Ozone layer hole. Image credit: NASA

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The ozone layer is a region in the Earth’s atmosphere that contains high concentrations of ozone. Ozone is three molecules of oxygen bonded together, and so it has the chemical symbol O3. The ozone layer contains more than 91% of the ozone in the Earth’s atmosphere. Because it absorbs ultraviolet radiation from the Sun, the ozone layer is vital to the evolution and survival of life on Earth.

Ozone in the Earth’s atmosphere is created when sunlight strikes oxygen molecules which consist of two oxygen atoms bonded together (O2). This splits it into two separate oxygen atoms which float in the atmosphere until they bond with other oxygen molecules creating ozone (O3). Ozone is unstable, though, and further ultraviolet radiation continues to break up the ozone into oxygen molecules and single oxygen atoms. This combination and breakdown is going all the time in the ozone layer.

The ozone layer is special to life because it absorbs ultraviolet radiation from the Sun in a very specific wavelength – UV-B radiation, between 315-280 nanometers in wavelength. It’s this UV-B radiation which gives us sunburns and can even cause cancer with long term radiation. Without the ozone layer, we would receive much more harmful radiation from the Sun.

Of course, one of the big worries in the last few years is the problem of ozone depletion. Certain manmade chemicals, like nitric oxide and chlorofluorocarbons break down ozone molecules, stopping them from being able to absorb ultraviolet radiation. A single molecule of one of these free radicals can break down more than 100,000 ozone molecules.

Satellites observing the Earth’s atmosphere discovered that the ongoing use of these chemicals were causing the ozone layer to thin out. Ozone layers declined at a rate of 4% per decade, mostly over the Earth’s northern and southern poles. Many countries enacted bans of ozone-destroying chemicals in 1978, and in the last few years scientists have determined that the rate of ozone depletion is slowing down.

We have written many articles about the ozone layer for Universe Today. Here’s an article about the ozone success story, and here’s an article about how the ozone layer really looks like it’s recovering.

Here’s more information on the ozone layer from NASA’s Ozone Resource Page. And here’s the ozone hole watch site.

In episode 36 of Astronomy Cast we discussed how an gamma ray burst could strip away the ozone layer of the Earth in just a moment.

Posted on by Fraser Cain

How Many Rings Does Jupiter Have?

Jupiter's rings. Image Credit: University of Maryland

We’re familiar with the rings of Saturn, but did you know that Jupiter has rings too? The rings of Jupiter were first discovered by the Voyager 1 spacecraft when it passed by Jupiter in 1979. The rings were investigated in more detail by NASA’s Galileo spacecraft during the 1990s. It was during the 1990s that Galileo and ground-based observations made a complete count of the number of Jupiter’s rings. So, how many rings does Jupiter have?

Jupiter is known to have 4 sets of rings: the halo ring, the main ring, the Amalthea gossamer ring, and the Thebe gossamer ring.

The halo ring is closest into Jupiter starting at a radius of 92,000 km and extending out to a radius of 122,500 km. The halo ring has a total width of 12,500 km.

Next is the main ring. It starts at 122,500 km and extends out to 129,000 km. It has a total width of only 6,500 km.

Outside these two major rings are the gossamer rings. These are very faint rings that are shepherded by two of Jupiter’s moons. The first is the Amalthea gossamer ring, which is shepherded by Jupiter’s moon Amalthea. It starts at a radius of 129,000 km from Jupiter and goes out to the orbit of Amalthea at 182,000 km.

Overlapping the Amalthea ring is the Thebe gossamer ring. It starts at a radius of 129,000 and goes out to a radius of 226,000 km.

How many rings does Jupiter have? The answer is four. Of course, it’s always possible that new rings will be discovered around Jupiter as new and better spacecraft and telescopes examine the planet.

We have written many articles about Jupiter and its rings for Universe Today. Here’s an article about how Jupiter’s rings are made in the shade. And here are some interesting discoveries made by NASA’s New Horizon’s spacecraft when it arrived at Jupiter.

Windows to the Universe has more information about Jupiter’s rings. And here’s more information on the rings from NASA.

We have recorded a whole episode of Astronomy Cast just about Jupiter, and in that episode we talked about the planet’s rings.

Reference:
NASA

Posted on by Fraser Cain

Milky Way Galaxy Pictures

Artist impression of the Milky Way. Image credit: NASA

Here are some beautiful pics of the Milky Way Galaxy. It’s important to remember that we live inside the Milky Way Galaxy, so there’s no way to show a true photograph of what the Milky Way looks like. We can see pictures of the Milky Way from inside it, or see artist illustrations of what the Milky Way might look like from outside.

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This Milky Way Galaxy picture shows what our galaxy would look like from above. You can see its spiral arms, dense core and the thin halo. The Milky Way is a common barred spiral galaxy. There are billions more just like it in the Universe.

Milky Way in infrared. Image credit: COBE
Milky Way in infrared. Image credit: COBE

This picture of the Milky Way was captured by NASA’s COBE satellite. This photograph was taken using the infrared spectrum, which allows astronomers to peer through the gas and dust that normally obscures the center of the Milky Way.

The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev
The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev

This image of the Milky Way Galaxy was taken with the Chandra X-Ray Observatory, which can see in the X-Ray spectrum. In this view, only high energy emissions are visible, such as the radiation emitted from black holes and other high energy objects.

Artist's concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way.Credit: NASA, ESA, and A. Schaller (for STScI)
Artist's concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way.Credit: NASA, ESA, and A. Schaller (for STScI)

Here’s an artist’s impression of what a galaxy like the Milky Way might have looked like early in its history. This image shows a supermassive black hole with young blue stars circling it.

Milky_Way_infrared_mosaic. Credit: Spitzer Space Telescope
Milky_Way_infrared_mosaic. Credit: Spitzer Space Telescope

This is a mosaic image of the Milky Way captured by NASA’s Spitzer Space Telescope. It was built up by several photographs taken by Spitzer, which sees in the infrared spectrum, and can peer through obscuring dust.

Posted on by Fraser Cain

Sun and Venus

Transit of Venus

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Venus is the second planet from the Sun, orbiting at an average distance of 108.2 million km. Venus takes a total of 224.7 days to orbit the Sun.

The Sun and Venus are vastly different sizes, of course. The diameter of Venus is 12,103 km, while the diameter of the Sun is 1.4 million km. In other words, the Sun is 115 times larger than Venus. You could fit about 1.5 million planets the size of Venus inside the Sun.

Venus is a terrestrial planet. It has a metal core surrounded by a mantle of silica rock. This is surrounded by a thin crust of rock. The Sun, on the other hand, is a massive ball of hydrogen and helium gas. Temperatures at its core are hot enough to ignite nuclear fusion – more than 15 million Kelvin.

The Sun has an enormous impact on Venus. The radiation from the Sun is trapped by the thick atmosphere of Venus, raising average temperatures across the planet to around 460 °C. In fact, this makes Venus the hottest planet in the Solar System.

Both the Sun and Venus formed at the same time, 4.6 billion years ago, with the rest of the Solar System. They formed out of the solar nebula, a cloud of gas and dust that collapsed down to become the Sun and planets.

Because Venus orbits closer to the Sun than the Earth, we always see it close to the Sun in the sky. Venus is either trailing the Sun or leading it across the sky. The best times to see Venus are just before sunrise or just after sunset.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

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

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

References:
NASA ISTP: Venus
NASA StarChild: Facts on Venus
NASA Facts: Magellan Mission to Venus

Posted on by Fraser Cain

Venus Conjunction

A conjunction of Venus occurs when Earth, Venus and the Sun are all lined up together. Imagine looking down at the Solar System from above and being able to straight line that goes through Earth, Venus and the Sun. That’s a conjunction of Venus.

There are two kinds of conjunctions that can happen: superior conjunction and inferior conjunction. A superior conjunction of Venus happens when Earth and Venus are on opposite sides of the Sun. Seen from above, it goes, Earth – Sun – Venus. An inferior conjunction of Venus occurs when Venus and Earth are on the same side of the Sun. So, if you drew a line it would go Sun – Venus – Earth.

From here on Earth, it’s not possible to see either inferior or superior conjunctions of Venus. When Venus is in a superior conjunction, it’s on the opposite side of the Sun, and the glare of the Sun is too bright to see it. The same situation happens with an inferior conjunction. In this situation, Venus is in between Earth and the Sun, and lost in the glare.

Because of the orbits of Venus and Earth, Venus very rarely passes directly in front of the Sun from our vantage point. This is called a transit of Venus, and it does occur every hundred years or so in pairs. The last transit of Venus was in 2004, and the next one will happen in 2012.

When there’s an inferior conjunction of Venus, the planet is approximately 41 million km away. It’s possible for Venus and Earth to get as close as 38.2 million km, but that happens rarely.

When seen through a telescope, Venus goes through phases, just like the Moon. When Venus is approaching its inferior conjunction, it becomes a thin sliver – but very bright. When it’s approaching a superior conjunction, we see it starting to look fully illuminated. It’s impossible to see Venus either in full inferior or superior conjunction because it gets lost in the glare of the Sun either way.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

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

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

Reference:
NASA: The Solar System

Posted on by Fraser Cain

Venus Period of Rotation

Venus captured by Magellan.

The period of rotation for Venus is 243 days. In other words, Venus takes 243 days to turn once on its axis so that the stars are in the same position in the sky.

That seems like a long time, and it is. Especially when you consider that a year on Venus only lasts 224.7 days. In other words, a day on Venus lasts longer than its year. Even stranger, Venus is rotating backwards from the rest of the planets. Seen from above its north pole, Venus is rotating clockwise, while the rest of the planets in the Solar System are turning counter-clockwise.

If you could actually stand on the surface of Venus, with the scorching heat and crushing atmospheric pressure, you would see the Sun rise in the West and then travel slowly across the sky, to set in the East. The total time from sunrise to sunrise is 116.75 days.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

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

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

Posted on by Fraser Cain

Does Venus Have Seasons?

Weather on Venus

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Venus is similar to Earth in size, mass, density to Earth. In many ways it’s Earth’s twin planets. Of course its climate is completely different, with its hellish temperature and crushing atmospheric pressure. Oh, and don’t forget about the clouds that rain sulfuric acid. But does Venus have seasons like Earth.

No.

Obviously, Venus doesn’t have nice warm summers and cooler winters like Earth; in fact, the surface of Venus experiences no temperature variations at all. Everywhere you go in the entire planet, the temperature is the same average 460 °C. It doesn’t matter if you’re near the equator or near the poles. Whether you’re on the day side or the night side, the temperatures don’t change much from the global average of 460 °C.

Part of the reason is the fact that the axial tilt of Venus is only 2.7°. That means that the planet has very little difference between the angle of its axis during “summer” and “winter”. Our axial tilt here on Earth is 23.4°, and that significant tilt means that the hemisphere pointed towards the Sun gets a lot more energy than the hemisphere pointed away.

And the other part of the reason why Venus doesn’t experience any temperature variations is because of the thick atmosphere – 93 times more surface atmospheric pressure than we experience here on Earth. This carbon dioxide atmosphere traps the heat and distributes it around the planet.

Even though the planet rotates very slowly, with spots on the planet experiencing more than 50 days of night, the temperatures just don’t fluctuate.

And so, this is why there are no seasons on Venus.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

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

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