The other 27 percent of the universe is made of this stuff, which is easier to detect than dark energy because astronomers can measure its gravitational effect on distant stars. Still, astronomers aren’t sure exactly what dark matter is. Two competing – and cutely named – theories attempt to explain dark matter’s contents: MACHOs, for Massive Compact Halo Objects such as small stars, and WIMPs, for Weakly Interacting Massive Particles left over from the big bang.
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Until recently, astronomers assumed that gravity was slowing the expansion of the universe that began with the big bang. At the end of the last century, however, they learned a shocking fact: The expansion was actually speeding up. The only way to explain this acceleration is that space is filled with… something else. Astronomers call this mystery matter ‘’dark energy.’’ They can’t see it, but they figure it has to exist everywhere, accounting for roughly 68 percent of the stuff in the universe. (Meanwhile, the atoms that make up planets, stars, your pet goldfish, and everything else account for less than 5 percent of the universe.)
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Some seriously strange stuff – and none of it good. Everything would go dark as your spaceship approached the black hole’s swirling ‘’event horizon,’’ or point of no return. The gravity here is so powerful that even light cannot escape the crushing singularity at the center. Your ship and body would stretch into an impossibly thin and long line, like toothpaste squeezed from its tube. As you approached the speed of light, time would slow and eventually stop, although you wouldn’t be alive to notice.
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Astronomers can’t see these mighty munchers of matter, but they spot their effects across the galaxy. Black holes form when stars 20 times larger than our own sun run out of fuel and go ‘’supernova” – or explode. The dying star’s core collapses under its own gravity until it scrunches into a singularity – or tightly packed point – smaller than an atom. Despite its tiny size, the singularity still packs a gravitational pull many times stronger than our sun. Like a cosmic whirlpool, the black hole pulls in anything – asteroids, planets, other stars, and even light – that gets too close.
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Because charged particles cast off from the sun hit the Earth’s magnetic field 100 miles (160 km) up, making the air molecules glow green, violet, blue or red. These curtains of light are called auroras. The best spots to see the aurora borealis (or northern lights) are Alaska, the northwestern regions of Canada, the southern tips of Iceland and Greenland, Norway, and Siberia, The aurora australis of Southern Hemisphere is trickier to see unless you live in Antarctica.
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That sunshine beaming through your windows might seem completely see-through, but this ‘’white light’’ is actually composed of many colors – a literal rainbow of them. Astronomer Isaac Newton noticed these colors than 300 years ago when he held a special piece of glass called a prism to the sunlight. The prism bent the light into its seven component colors, or wavelengths. Raindrops in the sky act like millions of tiny prisms, scattering the sunlight into its seven colors. A rainbow blossoms into living color when you see it from sunny spot, which is why it looks like rainbows form after a storm.
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