It's easy to use a star chart to identify constellations on a cloudless night. After all, the positions of these celestial objects have been mapped for centuries. But what happens when a guest star suddenly appears among its well-documented peers? It's probably the remains of a star that exploded hundreds or millions of years ago, and whose light is only now reaching our skies.
It doesn't take a professional degree to make an astronomical discovery. In January 2011, a 10-year-old girl found a supernova in a galaxy 240 million light-years away [source: Vincent]. Scientists often rely on backyard astronomers to patrol the skies for newly appearing pinpoints that are brighter and clearer than the objects around them. Stars about to go supernova change color from red to blue due to their increasing temperatures [source: Minkel]. And supernovae maintain some blue color due to the Doppler effect: The light from their explosions moves toward us so fast that it appears blue [source: Murdin]. Plus, unlike a comet or commercial airplane, a supernova won't waver from its position.
If you spot a supernova that isn't on record, you can report it to the IAU Central Bureau for Astronomical Telegrams. From there, astronomers will study any electromagnetic radiation that the potential supernova is giving off -- that is, any gamma rays, x-rays, ultraviolet waves, visible light, infrared waves, microwaves and radio waves. This spectrum of visible and invisible radiation will help them learn about what the celestial object is composed of, how hot it is, how dense it is and how fast it's moving.
Astronomers living in ancient China made the first record of a supernova some 2,000 years ago. They didn't understand what they were seeing and were convinced that the point of light was a new one. However, after chronicling the "new" star for eight months, the object suddenly disappeared. Although this hide-and-seek star could have become a forgotten footnote, the discovery experienced a revival in 2006. That's when astronomers realized they were looking at remnants of the same supernova that had been documented in ancient China [source: Zielinski].
Supernovae like this have been found all over the cosmos, in our galaxy and other galaxies millions of light-years away. In 1987, we discovered a supernova so close to Earth that it could be seen without looking through a telescope. This supernova was located in the Large Magellanic Cloud, neighbor to our Milky Way galaxy [source: Space Telescope Science Institute]. It made history again in 2011, when scientists discovered its debris glowing brighter as it entered a new stage of decay. The light of this supernova remnant became more visible because its leftover mass of debris expanded and bumped into a ring of debris that had been discharged from the supernova before it exploded. When the matter collided, it produced x-rays and heat, which caused the remnant to look brighter [source: Beck].
But how did this star begin to self-destruct in the first place? Learn about the life cycle of giant stars on the next page.