Astronomy: The Size of Stuff

The vast majority of objects out there in the universe are pretty big…moons, planets, stars, galaxies, so it can be difficult sometimes to get your head round their actual size. Here you’ll see how some space stuff out there compares to Earth stuff down here…

Neutron Star

This is how a typical neutron star would compare if it was on Earth, easily fitting right between Liverpool and Warrington in the north west of England. A star that is only around 20 kilometres across? Yes, but this is not any normal run of the mill star you’d see shining in the night sky, this thing is a weird and exotic object. A neutron star also crams in over 1.5 times the mass of the Sun into a tiny ball maybe not much bigger than your daily commute to work, and the Sun is huge (see the size of the Sun later). So this thing is incredibly dense, so dense in fact that just a tea spoon of it would weigh over a billion tonnes, and if you could stand on its surface you’d feel the gravitational pull of 200 billion times that of our planet…not that you’d ever survive it of course.

Of all the animals in the galactic zoo, neutron stars are amongst the strangest things out there. But these things do something else, they also spin. You probably own a kitchen blender, or you’ve seen one in action. Imagine a globe 20-30 kilometres across spinning faster than your kitchen blender, and the fastest known neutron star spins at 716 times a second. Their spin rates are extremely reliable, they are so accurate they even surpass an atomic clock, they’re natures most precise timepieces.

That’s a neutron star, an object not much bigger than a city, with the mass of 1.4 to 3.2 times the mass of our Sun, and spinning at a phenomenal rate.

Olympus Mons

Mars is actually quite a small world but it does things on a big scale. Located in the Tharsis Montes region of Mars is a volcano, it’s the biggest volcano on Mars, bigger than any volcano on Earth, in fact it’s the biggest volcano in the whole solar system. The volcano in question is called Olympus Mons, an extinct shield volcano with a truly colossal size. See how it appears on Mars in this Nasa illustration (above centre). On the image above you can see how it would appear if it was in the state of Arizona. Taller than 3 Mount Everest’s above sea level, this monster volcano actually would be Arizona as it completely covers it.

It is 374 miles (624 km) across, it towers 16 miles into the martian sky, and is rimmed by a 4 mile high cliff. At the summit of this colossal structure is the caldera at 50 miles across, easily seen in the image above. Olympus Mons has other volcanic company, in the Tharsis Montes region are three other smaller volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons that form a line to Olympus Mons’ south east.

Jupiter’s Moon Io

Jupiter’s moon Io is the solar system’s most volcanic body, looking like a cheese pizza it would fit between San Francisco and Detroit at 1,942 miles across or 3,636 kilometres. This moon of Jupiter is a similar size as Earth’s own Moon (2,160 miles), so you could do roughly the same size comparison above. Io is tiny compared to Jupiter though, this image shows Io floating above the gas giant’s raging storms far below…far far below in fact, Jupiter is actually 350,000 km away from Io, or roughly 2.5 Jupiters.

Io is the first of four main moons to Jupiter, and this is why it is covered in erupting volcanoes. Jupiter’s immense gravity pulls on and flexes Io as it travels around in its orbit. This gravitational influence from jupiter keeps the interior of Io molten and those volcanoes on its surface spewing lava on its surface, and covering its plains in yellow sulphur. Those volcanoes erupt high above the surface, so high that if they were on Earth their volcanic material would go past the International Space Station.

Mars

Earth’s sister planet Mars boasts some huge structures such as Olympus Mons and Valles Marineris, but the planet isn’t actually that big. In the image above see how big the United States and Canada would be if it was on the red planet. So if you could take a plane from one side of Mars to the other, it would take probably around 8 hours or so. This rusty desert world orbiting between Earth and Jupiter is only 53% the size of our planet, measuring 4,220 miles (6,792 km) at its equator, band from pole to pole it is 25 miles (40 km) smaller. This is why when viewed in a telescope Mars is always pretty small compared to planets like Jupiter and Saturn for example, although that doesn’t mean you can’t see features on this mysterious world. Through a decent sizes telescope you can see the ice caps and dark and lighter land features.

Earth’s rusty neighbour in the solar system is the second smallest of the planets, Mercury being smallest. The actual dry land mass of Mars is around the same as Earth’s, because although Mars is much smaller it doesn’t of course have any seas, you’ll have to go back a few billion years to see cool blue water slopping about on Mars.

Saturn

Jupiter holds the title for being the biggest planet in the solar system, but Saturn is no tiddler. It can hold its own in the size stakes, being 14, 514 miles smaller than Jupiter across its disk, and it also sports those fabulous rings. You can see just how Saturn dwarfs Earth in the image above, with nearly 6 Earths lining up across the width of its rings. The main dark gap in its rings is called the Cassini Division, this alone could almost contain the whole United States. Across the main planet’s disk of Saturn you could fit nearly 10 Earths, and if you could fill the inside of Saturn with Earths it would hold 764.

Saturn’s Rings

We’ll stay with Saturn for the minute to emphasise just how gigantic the extent of Saturn’s rings are. The main disk of Saturn has been taken out and replaced with Earth on the same scale. Saturn’s icy rings are composed of billions of particles from tiny grains right up to mountain sized chunks. The ring’s thickness is 1 kilometre, and they span around 175,000 miles (282,000 km) from inner ring to outer, that’s around 3 quarters the distance from the Earth to the Moon.

Jupiter

Jupiter is the king of the solar system, it has more mass than all the other planets and moons put together, and spans a whopping 88, 846 miles (142, 984 km) at the equator. It is over 11 times the diameter of our planet, with lightening bolts up to 1,000 times more powerful than Earth’s, and wind speeds in the upper atmosphere that can reach 100 metres per second. This planet races around in just 10 hours compared to Earth’s 24, making it the fastest rotating planet in the solar system. The image above shows the gas giant with how North America and Canada would appear to the same scale, it is completely dwarfed by Jupiter’s Great Red Spot, a storm that has been raging since possibly the year 1665.

The Sun

The Sun has far more mass than everything else in the solar system put together, in fact it is 99.86% of it. Which means that us and the other planets and moons are really just the left over rubble from the formation of the Sun 4.5 billion years ago…the cosmic byproducts. At the Sun’s scale Earth is now really starting to look puny, in the image above solar prominences visible along its limb explode into space many times the height of the Earth. A typical sunspot usually visible on most days on the Sun (with only the right equipment and know how), could easily dwarf Earth.  Across the Sun’s disk you could fit 109 Earths side by side, and to fill the Sun’s volume would take 1,300,000 Earths. On closer inspection the Sun has a granular or cellular appearance, these granules on the photosphere are the tops of convective cells that are plasma rising up from below. The solar disk has up to 4 million of these granules across its disk at any one time, and are on average the size of Texas.

The Sun puts out more energy in 1 second than has ever been produced in all of human history, and loses 4 billion tonnes of material into space every second but has enough to last for another 5 billion years. A solar flare, an explosion from the Sun’s surface caused when hugely powerful magnetic fields break apart under stress, can have the power of a billion Hiroshima bombs.

The Sun is only one among hundreds of billions of other stars in our Galaxy The Milky Way, but is larger than the average star.

By John Brady

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