From the perspective of an Earthling, outer space is a zone that occurs about 100 kilometers (60 miles) above the planet, where there is no appreciable air to breathe or to scatter light. In that area, blue gives way to black because oxygen molecules are not in enough abundance to make the sky blue.
Further, space is a vacuum, meaning that sound cannot carry because molecules are not close enough together to transmit sound between them. That’s not to say that space is empty, however. Gas, dust and other bits of matter float around “emptier” areas of the universe, while more crowded regions can host planets, stars and galaxies.
No one knows exactly how big space is. The difficulty arises because of what we can see in our detectors. We measure long distances in space in “light-years,” representing the distance it takes for light to travel in a year (roughly 5.8 trillion miles, or 9.3 trillion kilometers).
The galaxy MACS0647-JD (inset) appears very young and is only a fraction of the size of our own Milky Way. The galaxy is about 13.3 billion light-years from Earth, the farthest galaxy yet known, and formed 420 million years after the Big Bang. Image taken by Hubble Space Telescope on Nov. 29, 2011, and released Nov. 15, 2012.
From the perspective of an Earthling, outer space is a zone that occurs about 100 kilometers (60 miles) above the planet, where there is no appreciable air to breathe or to scatter light. In that area, blue gives way to black because oxygen molecules are not in enough abundance to make the sky blue.
Further, space is a vacuum, meaning that sound cannot carry because molecules are not close enough together to transmit sound between them. That’s not to say that space is empty, however. Gas, dust and other bits of matter float around “emptier” areas of the universe, while more crowded regions can host planets, stars and galaxies.
No one knows exactly how big space is. The difficulty arises because of what we can see in our detectors. We measure long distances in space in “light-years,” representing the distance it takes for light to travel in a year (roughly 5.8 trillion miles, or 9.3 trillion kilometers).
From light that is visible in our telescopes, we have charted galaxies reaching almost as far back as the Big Bang, which is thought to have started our universe 13.7 billion years ago. This means we can “see” into space at a distance of almost 13.7 billion light-years. However, astronomers are not sure if our universe is the only universe that exists. This means that space could be a lot bigger than it appears to us.
Radiation invisible to human eyes
Most of space is relatively empty, meaning that there are just stray bits of dust and gas inside of it. This means that when humans send a satellite to a distant planet, the object will not encounter “drag” in the same way that an airplane does as it sails through space.
The vacuum environment in space and on the moon, for example, is one reason that the lunar lander of the Apollo program looks so odd-shaped — like a spider, one crew said. Because the spacecraft was designed to work in a zone with no atmosphere, there was no need for smooth edges or an aerodynamic shape.
While space may look empty to human eyes, research has shown that there are forms of radiation emanating through the cosmos. In our own solar system, the solar wind — made up of plasma and other particles from the sun — permeates past the planets and occasionally causes aurora near the Earth’s poles. Cosmic rays also fly through the neighborhood, emanating from supernovas outside of the solar system.