Author: Fraser Cain

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We know the surface of the Earth is made of rock, we can examine it ourselves. But what is the center of the Earth made of? Well, reach into your pockets and pull out some coins. That’s roughly what the center of the Earth is made of.

The Earth is broken up into layers. The outermost layer is the crust- that’s what you’re standing on. About 30 km below your feet is where the next layer of the Earth, the mantle, starts. The mantle makes up the majority of the interior of the Earth, and its composed of heated rock under high pressure. But inside the mantle is the core of the Earth, and it’s made of metal.

The Earth’s core is broken up into two distinct regions. The inner core is a sphere of solid metal that measures about 2,440 km across. It’s believed to be comprised of 80% iron and 20% nickel. Surrounding this solid inner core is an outer core of liquid metal that extends for approximately another 2,000 km. Geologists believe that the movement of metal in the outer core gives the Earth its magnetic field, allowing compasses to work.

Needless to say, the center of the Earth is incredibly hot. Scientists estimate that the core of the Earth could get as hot as 7,000 kelvin, and about 5,700 kelvin at the border between the inner and outer cores.

We’ve written many articles about the core of the Earth. Here’s an article about how far down the center of the Earth is, and here’s an article about the center of the Earth.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

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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.

We’ve written many articles about deserts for Universe Today. Here’s an article about the Atacama desert, seen from space, and here’s an article about the largest desert in the world.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

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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.

We’ve written many articles about the Milky Way for Universe Today. Here’s an article about how many stars are in the Milky Way, and here’s an article about how many planets there are in the Milky Way.

If you’d like more info on the Milky Way, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We’ve also recorded an episode of Astronomy Cast all about the Milky Way. Listen here, Episode 99: The Milky Way.

Source: NASA

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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.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

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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.

We’ve written many articles about the Sun for Universe Today. Here’s an article with interesting facts about the Sun, and here’s an article about how big the Sun is.

If you’d like more info on the Sun, check out NASA’s Solar System Exploration Guide on the Sun, and here’s a link to the SOHO mission homepage, which has the latest images from the Sun.

We’ve also recorded an episode of Astronomy Cast all about the Sun. Listen here, Episode 30: The Sun, Spots and All.

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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.

We’ve written many articles about Uranus for Universe Today. Here’s an article about the color of Uranus, and here’s an article about some interesting Uranus facts.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We’ve also recorded an entire episode of Astronomy Cast just about Uranus. Listen here, Episode 62: Uranus.