SPACE IS NOT THAT FAR. It’s just under 300 miles away, or the distance from Phoenix to Los Angeles, or from Pittsburgh to Philadelphia. Sure, you have to go through a few layers of atmosphere to get there, but it’s pretty close. After that, however, the distances get really extreme. Here’s what you have to get through to reach space.
Troposphere (Fig. A): from ground level up to 12 miles. This is where clouds and almost all the water vapor over Earth exist. Mt. Everest reaches almost halfway up through it.
Stratosphere (Fig. B): 12 miles to 30 miles up. The stratosphere absorbs a lot of the sun’s radiation, so a lot of chemical reactions occur in this layer. It is also where the ozone layer exists.
Mesosphere (Fig. C): from 30 miles to 50 miles up. Here’s where heat begins to completely disappear from the atmosphere. Many gases are trapped in this layer, which is where objects hitting the atmosphere tend to burn up. Clouds made of ice also exist here.
Thermosphere (Fig. D): from 50 to about 250 miles up. This is where space starts turning black because there aren’t enough molecules to scatter light. Atoms are so far apart that they can become electrically charged by the sun’s radiation, and radio waves from some broadcasts are bounced off them so that they will travel beyond the horizon. The space shuttle and lower-Earth orbit satellites operate here, at about the 103-mile mark.
Exosphere (Fig. E): from 250 miles on to the rest of the universe. Space starts here, the last part of the atmosphere where molecules and gases can leave Earth. Space is thought of as a vacuum where atoms are spread out so far that they don’t form molecules of anything—although in reality, some gases still exist in space.
Satellite band: 22,300 miles up. This is the orbit in which satellites can hold a fixed position above a specific point. At this height, a satellite is traveling at the same speed at which the Earth rotates because it is at the far edge of our planet’s gravitational pull. Most satellites are placed in this geostationary orbit, meaning they stay fixed above one particular point on the Earth all the time. At 22,300 miles up, temperatures are at absolute zero (-459° Fahrenheit).
Astronomers measure distance in space by light-years, because miles are too small. It would be like trying to measure the United States in inches. Would you rather say 190,080,000 inches or 3,000 miles? A light-year equals 5.88 million million miles (a trillion miles), and is the distance light travels in one year, at the speed of 186,282 miles per second. Some good space distances to know are:
Moon (Fig. F): 238,854 miles away. It’s the closest object in the solar system to Earth.
Mars (Fig. G): 36,000,000 miles away (at its closest). It’s our nearest planetary neighbor.
Sun (Fig. H): 93,000,000 miles away. It takes about eight minutes for light from the sun to reach Earth. That means that if something happened on the sun right this second, we wouldn’t see it for another eight minutes.
Proxima Centauri (Fig. I): This is the nearest star to our sun; it is 4.3 light-years away.
The distances in space are hard for us to imagine. So try this: Let’s make the sun the size of a volleyball. If it were this small, then Earth would be the size of a pinhead and Jupiter, the largest planet, would be as big as a marble. At this size, our Milky Way Galaxy is about the size of a huge shopping mall and its parking lot, with the volleyball and pinhead and marble sitting on the ground next to one another. And even at this size, Proxima Centauri is still 4,000 miles away. That means if our shopping mall galaxy were located in New York, our nearest neighbor would be in Rome, Italy.
