Hijaz Mountains and Nafud Desert, Saudi Arabia June 1991
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Seen from space, the majority of the Earth’s surface is covered by oceans – that makes up 71% of the surface of the Earth, with the remaining 29% for land. But what percentage of the Earth’s land surface is desert? Deserts actually make up 33%, or 1/3rd of the land’s surface area.
That might sound like a surprisingly large amount, but that’s based on the official definition of a desert. Desert are any region on Earth that can have a moisture deficit over the course of a year. In other words, they can have less rainfall in a year than they give up through evaporation.
You would think that deserts are hot, but there are cold deserts too. In fact, the largest cold desert in the world is the continent of Antarctica. There are barren rock fields in Antarctica that never receive snow, even though they’re incredibly cold. The largest hot desert is the Sahara desert, in northern Africa, covering 9 million square kilometers.
Radio images of the quasar 3C 196 at 4 - 10 m wavelength (30 - 80 MHz frequency). Left: Data from LOFAR stations in the Netherlands only. The resolution is not sufficient to identify any substructure. Right: Blow-up produced with data from the German stations included. The resolution of this image is about ten times better and allows for the first time to distinguish fine details in this wavelength range. The colours are chosen to resemble what the human eye would see if it were sensitive to radiation at a wavelength ten million times larger than visible light. Image: Olaf Wucknitz, Bonn University (Click to enlarge image).
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Just eight of the eventual forty-four antenna stations for the LOw Frequency ARray (LOFAR) were combined to produce the first high-resolution image of a distant quasar at meter radio wavelengths. The first image shows fine details of the quasar 3C 196, a strong radio source several billion light years away, observed at wavelengths between 4 and 10 m. “We chose this object for the first tests, because we know its structure very well from observations at shorter wavelengths,” said Olaf Wucknitz from Bonn University. “The goal was not to find something new but to see the same or similar structures also at very long wavelengths to confirm that the new instrument really works. Without the German stations, we only saw a fuzzy blob, no sub-structure. Once we included the long baselines, all the details showed up.”
Five stations in the Netherlands were connected with three stations in Germany. To make detailed observations at such low frequencies, the telescopes have to be spaced far apart. When complete, the LOFAR array span across a large part of Europe.
Observations at wavelengths covered by LOFAR are not new. In fact, the pioneers of radio astronomy started their work in the same range. However, they were only able to produce very rough maps of the sky and to measure just the positions and intensities of objects.
“We are now returning to this long neglected wavelength range”, says Michael Garrett, general director of ASTRON, in The Netherlands, the institution that leads the international LOFAR project. “But this time we are able to see much fainter objects and, even more important, to image very fine details. This offers entirely new opportunities for astrophysical research.”
“The high resolution and sensitivity of LOFAR mean that we are really entering uncharted territory, and the analysis of the data was correspondingly intricate”, adds Olaf Wucknitz. “We had to develop completely new techniques. Nevertheless, producing the images went surprisingly smoothly in the end. The quality of the data is stunning.” The next step for Wucknitz is to use LOFAR to study so-called gravitational lenses, where the light from distant objects is distorted by large mass concentrations. High resolution is required to see the interesting structures of these objects. This research would be impossible without the international stations. IS-DE1: Some of the 96 low-band dipole antennas, Effelsberg LOFAR station (foreground); high-band array (background) (Credit: James Anderson, MPIfR)
LOFAR will consist of at least 36 stations in the Netherlands and eight stations in Germany, France, the United Kingdom and Sweden. Currently 22 stations are operational and more are being set up. Each station consists of hundreds of dipole antennas that are connected electronically to form a huge radio telescope that will cover half of Europe. With the novel techniques introduced by LOFAR, it is no longer necessary to point the radio antennas at specific objects of interest. Instead it will be possible to observe several regions of the sky simultaneously.
The resolution of an array of radio telescopes depends directly on the separation between the telescopes. The larger these baselines are relative to the observed wavelength, the better the achieved resolution. Currently the German stations provide the first long baselines of the array and improve the resolution by a factor of ten over just using the Dutch stations. ASTRON officials say the imaging quality will improve significantly as more stations come online.
“We want to use LOFAR to search for signals from very early epochs of the Universe,, said Benedetta Ciardi from the Max-Planck-Institut für Astrophysik (MPA) in Garching. “Having a completely theoretical background myself, I never had thought that I would get excited over a radio image, but this result is really fascinating.”
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Head outside at night, far away from bright cities and you’ll see a beautiful streak of light splashed across the sky. That’s the Milky Way; of course, it’s really the vast collection of stars contained in our home galaxy. But who discovered the Milky Way?
There’s no way to know who actually first noticed the Milky Way. You can see it with your unaided eyes, so our paleolithic ancestors would have seen the Milky Way every clear night. So perhaps a better question to ask might be, “who discovered that the Milky Way is a galaxy”?
Ancient Greek philosophers proposed that that Milky Way might be a vast collection of stars, to dim to make out individually. But the first actual proof came when Galileo Galilei pointed his first rudimentary telescope at the Milky Way in 1610, and was able to see that the Milky Way was made up of countless stars.
In 1755, Immanuel Kant proposed that the Milky Way was a large collection of stars held together by mutual gravity. Just like the Solar System, this collection of stars must be rotating and flattened as a disk, with the Solar System embedded within the disk. Uranus discoverer William Herschel attempted to actually map out the shape of the Milky Way in 1785, but he didn’t realize that large portions of the galaxy are obscured by gas and dust, which hide its true shape.
It wasn’t until the 1920s, when Edwin Hubble provided conclusive evidence that the spiral nebulae in the sky were actually whole other galaxies. This helped astronomers to understand the true nature and shape of the Milky Way, and also discover the true size and scale of the Universe around us.
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Volcanoes occur when hot magma from inside the Earth reaches the surface and erupts as lava, ash and rock. So we know the interior of the Earth is hotter than the surface. But how hot is the core of the Earth?
The Earth is roughly a sphere, with a radius of 6,371 km. In other words, you’d need to dig a tunnel down 6,371 km to reach the center of the Earth; it’s hottest place. Geologists believe that the core of the Earth is made up of metals, like iron and nickel, and it’s probably in a solid state, surrounded by a shell of liquid metal. The inner core is the hottest part of the Earth, and measures 2,440 km across.
It’s down in this inner core where you’d find the hottest part of Earth. Scientists have estimated that the temperature of the core reaches 5,700 kelvin (5,430 °C; 9,800 °F).
We’ve written many articles about the interior of the Earth. Here’s an article about the Earth’s interior, and here’s an article about the layers of the Earth.
With our proper place in the Universe worked out, and some powerful telescopes to probe the cosmos, astronomers started making some real progress. The next few hundred years was a time of constant refinement, with astronomers discovering new planets, new moons, and developing new theories in astronomy and physics.
Now we reach time with names that many of you will be familiar: Galileo, Kepler, Copernicus. This is an age when the biggest names in astronomy used the best tools of their time to completely rearrange their understanding of the Universe, putting the Earth where it belonged – merely orbiting the Sun, and not the center of everything.
And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let Fraser know if you can be a host, and he’ll schedule you into the calendar.
Finally, if you run a space-related blog, please post a link to the Carnival of Space. Help us get the word out.
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Shield volcanoes are some of the largest volcanoes in the world. For example, Mauna Kea and Mauna Loa on the big island of Hawaii are examples of shield volcanoes. And so is Olympus Mons on Mars, which towers 27 km above the surrounding plains. But how are shield volcanoes formed?
Shield volcanoes form like any volcanoes. They’re spots on the Earth where magma from inside the Earth has reached the surface, and becomes lava, ash and volcanic gasses. Over the course of many eruptions, a volcano builds up layer by layer until the magma chamber underneath it goes empty and the volcano goes dormant.
The main difference with shield volcanoes is that they’re formed out of lava flows which have a low viscosity. Think of liquids. Water is very runny, and has a low viscosity. Syrup, on the other hand, has a high viscosity and flows more slowly. The shape and nature of a volcano depends on the viscosity of the magma. With shield volcanoes, the lava flows easily for many kilometers, creating the gently sloping sides. Shield volcanoes are much less dangerous than other types of volcanoes; they typically don’t explode, and the lava flows are easy to avoid – if you’re in a car or walking.
The kind of lava that has low viscosity is basaltic lava, which typically erupts at temperatures higher than 950 °C. If flows easily, forming puddles, channels and rivers of molten lava.
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I got this strange question by email a few days ago, so I thought I’d tackle it: “Is the Earth Bigger than the Sun?”. Nope, the Sun is much, much bigger than the Earth. From here on Earth, the Sun looks smaller than the Earth, but that’s only because you’re much closer to the Earth than the Sun. You’re standing on the surface of the Earth, while the Sun is 150 million km away.
But if you could get far enough away that both the Earth and the Sun are the same distance, you’d see the real size difference. The diameter of the Sun is 1,390,000 km. Just for comparison, the diameter of the Earth is only 12,742 km. This means that you could put 109 Earths side-by-side to match the diameter of the Sun. And if you wanted to try and fill up the Sun with Earths, it would take 1.3 million Earths to match the volume of the Sun.
The Sun is the largest, most massive object in the Solar System by far. It accounts for 99.86% of the mass of the Solar System, with most of the remaining mass taken up by Jupiter, which is the largest planet in the Solar System.
You might be surprised to know that there are many stars which are much larger than the Sun. The red supergiant star Betelgeuse, in the constellation of Orion, is thought to be 300-500 times larger than the Sun. And the largest known star, VY Canis Majoris, it believed to be 1800-2100 times larger than the Sun; at the very theoretical limit of star sizes.
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Were you wondering who discovered Uranus and when? Uranus is the first planet that was actually discovered in modern times. Although you can just barely see it with the unaided eye, it wasn’t discovered until March 13, 1781 by the German-born astronomer Sir Frederick William Herschel.
Herschel was working with a 7-foot long Newtonian telescope – these use curved mirrors to magnify – cataloging stars down to 8th magnitude. These are stars so dim that you can’t see them with the unaided eye, but they’re visible in a small telescope or good binoculars. During this survey he noticed that one star wasn’t point-like, but seemed to have a planet-like disk. He originally thought that it was a comet or nebula, but another astronomer calculated its motion and determined that it followed a planetary orbit around the Sun.
Since he was working in England at the time, with King George III as a patron, Herschel wanted to call the planet Georgian star, after the king. But the astronomical society had other ideas, and wanted to follow the tradition of naming planets after Roman gods. So it was named Uranus, after the father of Saturn and grandfather of Zeus.
Although Herschel was the first to properly recognize Uranus as a planet, it had been observed several times before. The English astronomer John Flamsteed had his observations of Uranus 6 times, but thought it was a star in the constellation of Taurus. And the French astronomer, Pierre Lemonnier, observed it at least 12 times – again thinking it was just a star.
