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1. Quasars These mysterious starlike objects shine from the outermost limits of the universe, helping scientists learn about the earliest stages of existence. We've since learned that a quasar is actually a black hole at the center of a huge, distant galaxy. Perhaps more interesting, quasars give off 1,000 times more energy than the entire Milky Way galaxy.
2. Lightweight Planets You may have learned that some planets in the solar system are gaseous, but did you know that Saturn, that blinged-out planet with all the rings, could float in water? The planet's density is 0.687 g/cm3 versus water's density of .998 g/cm3. So Saturn would make an awesome rubber ducky in the universe's largest bathtub.
3. Liquids in Space Here on Earth, liquids tend to flow downward. But in the zero-gravity vacuum of space, any liquid will shape itself into a sphere. It is surface tension, the same phenomenon that causes water to form as a horizontal surface on Earth, that causes liquids to form spheres in space.
4. Goodbye, Moon Tidal effects cause the moon to move about 3.8 cm away from Earth every year. It's a process called tidal acceleration, the aggregate of competing gravitational forces between a planet and its satellite. As a result, the Earth's rotation slows down at about .002 seconds a century, and the moon casually inches toward our sister, Venus.
5. Old Light Believe it or not, the sunlight we see today is actually 30,000 years old. That's when the energy of sunlight was created in the sun's core, and it has since then been fighting to penetrate the dense matter of the sun. Once it reaches the surface, the light takes only about eight minutes to reach us.
6. Extra Moons? In 1986, a scientist named Duncan Waldron discovered an asteroid in elliptical orbit around the sun that seemed to mimic Earth's revolution. Because the asteroid appeared to be following our planet, it was sometimes referred to as Earth's second moon. Since then, at least three similar asteroids have been discovered.
7. Cold Welding In space, pressing two uncoated pieces of metal will eventually fuse them together. The Earth's atmosphere coats metallic surfaces with a layer of oxidized material, but in the vacuum of space, that layer barely exists. NASA used to be hyper-sensitive to cold welding, so the metal used in many spaceships is coated to prevent the reaction. But it takes more than a brief bump for two metals to fuse in space, and in the 1960s the phenomenon of instant, accidental cold welding was dispelled as a myth.
8. Extra Inches All human beings are about two inches taller in space. On Earth, gravity compresses the spine, but in the vacuum of space, the spring-like spine is free to elongate. The bad news? Back on Earth, they shrink back down to normal height.
9. Diamond Star In 2004, astronomers discovered a star composed entirely of diamond, measuring 4,000 km across and 10 billion trillion trillion carats. 50 light years from Earth, the diamond star is classified as a crystallized white dwarf, the hot core that remains after a star burns out. Only recently have scientists been able to study the contents of the white dwarf, and they've confirmed that the crystallized carbon interior of the star is, in fact, the galaxy's largest diamond.
10. Shrinking Sun Solar winds are streams of charged particles ejected from the upper atmosphere of the sun that cause it to lose up to a billion kilograms of mass a second. For such an extreme dieting regimen, the sun still looks pretty dang enormous.
11. Lasting Footprints Due to the absence of air and wind on the moon, all astronaut footprints last for millions of years, longer than the most permanent structures on Earth. As long as a meteor or any other space particle does not hit the moon, any impressions made into its surface will virtually last forever.
12. Electrostatic Levitation During the first Apollo missions, astronauts reported a hazy glow on the moon's horizon that looked a little like an atmosphere. This was weird since, well, the moon doesn't have an atmosphere. The glow was actually the sun's reflection of floating dust particles. Because the sunlight gives an electrostatic charge to dust particles on the moon, some particles float in the air, a process known as electrostatic levitation.
13. Long Day Amazingly, a single day on Venus is longer than its entire year. It takes Venus 243 Earth days to completely rotate on its axis, but just 225 days to orbit the sun. Stranger still, Venus is one of two planets that rotates in reverse, a phenomenon called retrograde motion. Most theories attribute the reverse rotation to an ancient planetary collision.
14. Milky Way Satellites Planets in the solar system aren't the only celestial bodies with satellites in orbit. The Milky Way galaxy itself has at least 15 satellite galaxies in orbit around it. Just as the moon is gravitationally bound to the Earth, these satellite galaxies are gravitationally bound to the Milky Way.
15. Cold Steel On the former planet Pluto (now designated a dwarf planet), the temperature is a brisk -390 degrees Fahrenheit. Expectedly, temperatures become progressively colder as you move away from the sun, and Pluto is about as far as you can get within our solar system. In fact, it is so cold that Pluto's ice is harder than steel.