The Lone Ranger
12-03-2004, 05:04 AM
Inspired by the “Bowl World” thread, I’ve been thinking about cosmic scales of distance. It simply blows the mind to contemplate such vast scales, or at least it blows mine anyway! So, for those who’re interested, I thought we might take a brief tour of our local environment. We’ll start here on Earth.
The Earth is a ball of rock afloat in a vast sea of emptiness. Well, okay, that sounds somewhat poetic, but it’s not especially accurate. The Earth’s inner core is solid nickel and iron; its outer core is liquid nickel and iron. The inner and outer core make up most of Earth’s mass, so it’s perhaps most accurate to say that Earth is a big ball of nickel and iron. The core is covered by the mantle, made up of semi-molten rock. Floating on the mantle is the crust of solid rock. How thick is the crust compared to the rest of the Earth? Well, if you take a standard classroom globe to represent the Earth, the crust would be about as thick as the paint on the globe’s surface.
The earth is almost 8,000 miles in diameter, a pretty big rock, no? Our nearest celestial neighbor, the moon, is a somewhat smaller ball of rock about 238,000 miles away. It’s amazing, when you think about it, that we’ve actually sent people there and brought them safely home again.
Think about the sun and you start dealing with somewhat larger numbers. Some 93 million miles away, our sun is a gigantic nuclear fusion reaction some 865,000 miles across. The sun consists almost entirely of hydrogen and helium; because of the tremendous weight of the overlying layers, hydrogen in the sun’s core is compressed until its denser than lead. At such a high pressure and temperature (about a [I]million degrees), the hydrogen fuses into helium, releasing energy as it does. A million Earth-sized planets could fit inside the sun, yet it is only a run-of-the-mill star, classified by astronomers as a “yellow dwarf” – a galactic lightweight.
If you were to start from the sun and travel outward some 36 million miles, you would encounter the planet Mercury. Named after the fleet-footed Roman messenger god, Mercury looks very much like a slightly larger version of our moon. (Mercury takes only 88 days to complete an orbit of the sun.) Like our moon, it is a cratered, essentially airless, and very hostile world. Because of Mercury’s proximity to the sun, temperatures on the day side reach 800 degrees Fahrenheit, so you probably wouldn’t want to stick around for a visit.
The next planet out from the sun is cloud-shrouded Venus, named for the Roman goddess of love and beauty. Venus orbits the sun at an average distance of about 67 million miles, and is often referred to as Earth’s “sister planet,” because it’s about the same size and density as the Earth. The similarities pretty-much end there though. Venus is covered by a dense atmosphere made up mostly of carbon dioxide. Because its atmosphere traps heat from the sun instead of allowing it to radiate away to space, Venus’ surface temperature is about 900 degrees Fahrenheit – hotter than Mercury’s, and hot enough to melt lead. As if that’s not bad enough, the clouds that shroud the planet are made of sulfuric acid. Were it ever to cool enough for rain to fall, Venus would have oceans of sulfuric acid. Definitely, Venus is not a place you’d want to visit.
As you continue your journey outward, you pass Earth, and then come to Mars, some 142 million miles out from the sun. Mars was named for the Roman god of war, because of its distinctly reddish color. That’s because of all the oxidized iron compounds on Mars’ surface – in effect, the planet is covered in rust.
On the way out from Mars, you’ll pass through the Asteroid Belt. You probably wouldn’t notice anything though. If you’ve seen The Empire Strikes Back and think that’s what an asteroid belt would look like, I can assure you that the reality is quite a lot less impressive. The Voyager space probes passed right through the densest part of the asteroid belt without ever coming close-enough to an asteroid to see it as anything other than a point of light.
Some 480 million miles out from the sun, you would encounter Jupiter, largest of the planets in our Solar System. At over 89,000 miles in diameter, the Earth would fit inside it 1,000 times over. Jupiter is made up mostly of hydrogen and helium, the same elements that make up most of the sun. Basically, a “gas giant” planet like Jupiter is a star that didn’t quite make it, and if Jupiter were only a little bigger (on a stellar scale), then the pressure at its core would be sufficient to ignite its nuclear fires and the Solar System would have not one but two suns.
The next planet you’d encounter is lovely, ringed Saturn. Saturn is some 887 million miles from the sun, and with a diameter of about 74,000 miles, is only a little smaller than Jupiter. Like Jupiter, Saturn is a “gas giant,” made up mostly of hydrogen and helium. Saturn has the distinction of being the only planet that’s less dense than water, and if a suitably large ocean could be found, Saturn would float. Saturn’s famous rings may be the remains of moons that were shattered by impacts with comets and asteroids, and/or moons that drifted too close to the planet and were torn apart by tidal forces.
Beyond Saturn, orbiting the sun at an average distance of almost 1.8 billion miles is the planet Uranus. Uranus is another gas giant, though it is “only” about 32,000 miles in diameter, and so much smaller than Jupiter or Saturn. Like Saturn, Uranus has rings, though they’re much less prominent than are Saturn’s. Compared to the other planets, Uranus has the distinction that it is lying on its side. This seems to be the result of a collision between Uranus and a massive, planet-sized object early in the history of the Solar System.
Normally, the next planet out from Uranus is Neptune. Neptune is a near twin of Uranus, some 31,000 miles in diameter and about 2.8 billion miles from the sun. Neptune, too, has rings, though they’re even less prominent than are those of Uranus.
Right now, the most distant of the planets is tiny, icy Pluto. It orbits at an average distance of some 3.7 billion miles from the sun, and is only some 1,400 miles in diameter – smaller than our moon. Pluto’s orbit is highly elliptical – so elliptical, in fact, that for part of each orbit Pluto is actually closer to the sun than is Neptune. Pluto crossed Neptune’s orbit in January of 1979 and remained within Neptune’s orbit until February of 1999, when it re-crossed Neptune’s orbit and resumed its position as the most distant planet. Pluto won’t cross Neptune’s orbit again until September of 2226. Because of it’s unusual nature – its small size, the fact that it appears to be made up largely of ice, and its strange orbit – many astronomers don’t consider Pluto to be a “true” planet. Indeed, Pluto may be a moon of Neptune’s that somehow “escaped” and began orbiting the sun independently.
Unimaginably vast as it is, our solar system is but a tiny speck, lost in the immensity of the galaxy, and the galaxy itself is but one among hundreds of billions scattered throughout the universe. To measure distances beyond the limits of the solar system, such earthly units as miles quickly become far too cumbersome – for example, the nearest star to our sun is over 25,000,000,000,000 miles away. Consider it this way: if the sun were only one foot in diameter, Proxima Centauri, the next-nearest star, would still be over 1,200 miles distant.
To express such distances, astronomers use the speed of light as the most convenient measuring device. Light, the fastest thing known, travels at the goodly clip of 186,282 miles per second – more than 670 million miles per hour. At this speed, a beam of light could circle the earth seven times in less than a second, or travel from the earth to the moon in less than two seconds. Traveling at the speed of light, the sun is a little over eight minutes distant, and Pluto is a little over five hours away. To get to Proxima Centauri would take over four years at the speed of light. Since the light from each of the stars you can see took years to reach us, when you look into the night sky you are looking back into time. That is, when you look at a star, you’re seeing it as it was when the light you’re just-now seeing left it, not as it is right now.
Logically enough, the distance that light travels in a year – about six trillion miles – is called a “light year,” and this is the unit most commonly used to measure interstellar distances. To take some examples, Barnard’s Star, the next-nearest star to our sun after the Centauri cluster is only about 6 light years away. Sirius, the brightest star in the nighttime sky is about 8.7 light years way. Aldebaran, the brightest star in the constellation Taurus is 68 light years away – from that distance, our sun wouldn’t even be visible without a telescope. Polaris, the North Star, is about 700 light years away, and giant Rigel, the brightest star in the constellation Orion is over 900 light years distant. When you look up at Rigel, you’re looking at light that left the star around the time of the Norman conquest of England.
All of these stars are our galactic neighbors, part of the Milky Way galaxy, an immense collection of stars about 100,000 light years across. The Milky Way contains over 100 billion stars, probably more stars than there are grains of sand on all the beaches of the world. Within this vast assemblage, our sun is only a minor star in the outer reaches of the galaxy. Traveling at 600,000 miles per hour, it takes the sun over 200 million years to complete just one orbit of the galactic center.
There are more galaxies scattered through the cosmos than there are stars in the Milky Way, and the Milky Way itself is only an average-sized galaxy amongst all the others. As far as we can tell, there is absolutely nothing unusual about it.
The nearest major galaxy to our own is the Andromeda galaxy, over 2 million light years away. If you live in the Northern Hemisphere, you can just see the Andromeda galaxy as a fuzzy patch of light near the northeastern horizon. This makes it the most distant object visible to the naked eye. Light reaching us today from Andromeda predates the human race, which has existed for much less time than it took the light to make that journey. A good telescope can pick up light from galaxies billions of light years away. In fact, the light we see from many of those galaxies began its journey before the earth had even formed, since the earth is “only” about 4.5 billion years old.
So the universe is unimaginably huge, and we humans and all our creations – all our hopes, dreams, wars, arts, sciences, et cetera – constitute only an unimaginably tiny portion of it. No king, no emperor, no president, has ever controlled a significant portion of the universe, nor has any empire ever existed for a significant portion of time, when measured on a cosmic scale. Some find that to be a depressing – or even frightening – thought, but personally, I find it rather enheartening. A universe so vast provides us with frontiers that we and our descendants can’t even hope to fully explore. But it will be fun to try.
Cheers,
Michael
The Earth is a ball of rock afloat in a vast sea of emptiness. Well, okay, that sounds somewhat poetic, but it’s not especially accurate. The Earth’s inner core is solid nickel and iron; its outer core is liquid nickel and iron. The inner and outer core make up most of Earth’s mass, so it’s perhaps most accurate to say that Earth is a big ball of nickel and iron. The core is covered by the mantle, made up of semi-molten rock. Floating on the mantle is the crust of solid rock. How thick is the crust compared to the rest of the Earth? Well, if you take a standard classroom globe to represent the Earth, the crust would be about as thick as the paint on the globe’s surface.
The earth is almost 8,000 miles in diameter, a pretty big rock, no? Our nearest celestial neighbor, the moon, is a somewhat smaller ball of rock about 238,000 miles away. It’s amazing, when you think about it, that we’ve actually sent people there and brought them safely home again.
Think about the sun and you start dealing with somewhat larger numbers. Some 93 million miles away, our sun is a gigantic nuclear fusion reaction some 865,000 miles across. The sun consists almost entirely of hydrogen and helium; because of the tremendous weight of the overlying layers, hydrogen in the sun’s core is compressed until its denser than lead. At such a high pressure and temperature (about a [I]million degrees), the hydrogen fuses into helium, releasing energy as it does. A million Earth-sized planets could fit inside the sun, yet it is only a run-of-the-mill star, classified by astronomers as a “yellow dwarf” – a galactic lightweight.
If you were to start from the sun and travel outward some 36 million miles, you would encounter the planet Mercury. Named after the fleet-footed Roman messenger god, Mercury looks very much like a slightly larger version of our moon. (Mercury takes only 88 days to complete an orbit of the sun.) Like our moon, it is a cratered, essentially airless, and very hostile world. Because of Mercury’s proximity to the sun, temperatures on the day side reach 800 degrees Fahrenheit, so you probably wouldn’t want to stick around for a visit.
The next planet out from the sun is cloud-shrouded Venus, named for the Roman goddess of love and beauty. Venus orbits the sun at an average distance of about 67 million miles, and is often referred to as Earth’s “sister planet,” because it’s about the same size and density as the Earth. The similarities pretty-much end there though. Venus is covered by a dense atmosphere made up mostly of carbon dioxide. Because its atmosphere traps heat from the sun instead of allowing it to radiate away to space, Venus’ surface temperature is about 900 degrees Fahrenheit – hotter than Mercury’s, and hot enough to melt lead. As if that’s not bad enough, the clouds that shroud the planet are made of sulfuric acid. Were it ever to cool enough for rain to fall, Venus would have oceans of sulfuric acid. Definitely, Venus is not a place you’d want to visit.
As you continue your journey outward, you pass Earth, and then come to Mars, some 142 million miles out from the sun. Mars was named for the Roman god of war, because of its distinctly reddish color. That’s because of all the oxidized iron compounds on Mars’ surface – in effect, the planet is covered in rust.
On the way out from Mars, you’ll pass through the Asteroid Belt. You probably wouldn’t notice anything though. If you’ve seen The Empire Strikes Back and think that’s what an asteroid belt would look like, I can assure you that the reality is quite a lot less impressive. The Voyager space probes passed right through the densest part of the asteroid belt without ever coming close-enough to an asteroid to see it as anything other than a point of light.
Some 480 million miles out from the sun, you would encounter Jupiter, largest of the planets in our Solar System. At over 89,000 miles in diameter, the Earth would fit inside it 1,000 times over. Jupiter is made up mostly of hydrogen and helium, the same elements that make up most of the sun. Basically, a “gas giant” planet like Jupiter is a star that didn’t quite make it, and if Jupiter were only a little bigger (on a stellar scale), then the pressure at its core would be sufficient to ignite its nuclear fires and the Solar System would have not one but two suns.
The next planet you’d encounter is lovely, ringed Saturn. Saturn is some 887 million miles from the sun, and with a diameter of about 74,000 miles, is only a little smaller than Jupiter. Like Jupiter, Saturn is a “gas giant,” made up mostly of hydrogen and helium. Saturn has the distinction of being the only planet that’s less dense than water, and if a suitably large ocean could be found, Saturn would float. Saturn’s famous rings may be the remains of moons that were shattered by impacts with comets and asteroids, and/or moons that drifted too close to the planet and were torn apart by tidal forces.
Beyond Saturn, orbiting the sun at an average distance of almost 1.8 billion miles is the planet Uranus. Uranus is another gas giant, though it is “only” about 32,000 miles in diameter, and so much smaller than Jupiter or Saturn. Like Saturn, Uranus has rings, though they’re much less prominent than are Saturn’s. Compared to the other planets, Uranus has the distinction that it is lying on its side. This seems to be the result of a collision between Uranus and a massive, planet-sized object early in the history of the Solar System.
Normally, the next planet out from Uranus is Neptune. Neptune is a near twin of Uranus, some 31,000 miles in diameter and about 2.8 billion miles from the sun. Neptune, too, has rings, though they’re even less prominent than are those of Uranus.
Right now, the most distant of the planets is tiny, icy Pluto. It orbits at an average distance of some 3.7 billion miles from the sun, and is only some 1,400 miles in diameter – smaller than our moon. Pluto’s orbit is highly elliptical – so elliptical, in fact, that for part of each orbit Pluto is actually closer to the sun than is Neptune. Pluto crossed Neptune’s orbit in January of 1979 and remained within Neptune’s orbit until February of 1999, when it re-crossed Neptune’s orbit and resumed its position as the most distant planet. Pluto won’t cross Neptune’s orbit again until September of 2226. Because of it’s unusual nature – its small size, the fact that it appears to be made up largely of ice, and its strange orbit – many astronomers don’t consider Pluto to be a “true” planet. Indeed, Pluto may be a moon of Neptune’s that somehow “escaped” and began orbiting the sun independently.
Unimaginably vast as it is, our solar system is but a tiny speck, lost in the immensity of the galaxy, and the galaxy itself is but one among hundreds of billions scattered throughout the universe. To measure distances beyond the limits of the solar system, such earthly units as miles quickly become far too cumbersome – for example, the nearest star to our sun is over 25,000,000,000,000 miles away. Consider it this way: if the sun were only one foot in diameter, Proxima Centauri, the next-nearest star, would still be over 1,200 miles distant.
To express such distances, astronomers use the speed of light as the most convenient measuring device. Light, the fastest thing known, travels at the goodly clip of 186,282 miles per second – more than 670 million miles per hour. At this speed, a beam of light could circle the earth seven times in less than a second, or travel from the earth to the moon in less than two seconds. Traveling at the speed of light, the sun is a little over eight minutes distant, and Pluto is a little over five hours away. To get to Proxima Centauri would take over four years at the speed of light. Since the light from each of the stars you can see took years to reach us, when you look into the night sky you are looking back into time. That is, when you look at a star, you’re seeing it as it was when the light you’re just-now seeing left it, not as it is right now.
Logically enough, the distance that light travels in a year – about six trillion miles – is called a “light year,” and this is the unit most commonly used to measure interstellar distances. To take some examples, Barnard’s Star, the next-nearest star to our sun after the Centauri cluster is only about 6 light years away. Sirius, the brightest star in the nighttime sky is about 8.7 light years way. Aldebaran, the brightest star in the constellation Taurus is 68 light years away – from that distance, our sun wouldn’t even be visible without a telescope. Polaris, the North Star, is about 700 light years away, and giant Rigel, the brightest star in the constellation Orion is over 900 light years distant. When you look up at Rigel, you’re looking at light that left the star around the time of the Norman conquest of England.
All of these stars are our galactic neighbors, part of the Milky Way galaxy, an immense collection of stars about 100,000 light years across. The Milky Way contains over 100 billion stars, probably more stars than there are grains of sand on all the beaches of the world. Within this vast assemblage, our sun is only a minor star in the outer reaches of the galaxy. Traveling at 600,000 miles per hour, it takes the sun over 200 million years to complete just one orbit of the galactic center.
There are more galaxies scattered through the cosmos than there are stars in the Milky Way, and the Milky Way itself is only an average-sized galaxy amongst all the others. As far as we can tell, there is absolutely nothing unusual about it.
The nearest major galaxy to our own is the Andromeda galaxy, over 2 million light years away. If you live in the Northern Hemisphere, you can just see the Andromeda galaxy as a fuzzy patch of light near the northeastern horizon. This makes it the most distant object visible to the naked eye. Light reaching us today from Andromeda predates the human race, which has existed for much less time than it took the light to make that journey. A good telescope can pick up light from galaxies billions of light years away. In fact, the light we see from many of those galaxies began its journey before the earth had even formed, since the earth is “only” about 4.5 billion years old.
So the universe is unimaginably huge, and we humans and all our creations – all our hopes, dreams, wars, arts, sciences, et cetera – constitute only an unimaginably tiny portion of it. No king, no emperor, no president, has ever controlled a significant portion of the universe, nor has any empire ever existed for a significant portion of time, when measured on a cosmic scale. Some find that to be a depressing – or even frightening – thought, but personally, I find it rather enheartening. A universe so vast provides us with frontiers that we and our descendants can’t even hope to fully explore. But it will be fun to try.
Cheers,
Michael