For thousands of years, the night sky was just a splash of random dots.
Over time, ancient peoples formed imaginary shapes by connecting the brighter points of light of a certain area of sky. Those shapes represented an object, person, animal, or even a god—the constellations.
Then came the mythologic stories and how they interacted in the celestial theatre. Those that looked at the sky regularly would notice a brighter than usual star or stars traverse a path across the sky over weeks, months, and years. Although it was not known at the time, these are the planetary members of our solar system.
The word planet comes from the early Greeks and means “wanderer” or “wandering star”, and for obvious reasons. Seen with the unaided eye are the planets Mercury, Venus, Mars, Jupiter, and Saturn. Uranus and Neptune were discovered via telescope in 1781 and 1846, respectively.
Pluto was discovered in 1930 but demoted to minor planet status in 2006, so the count remains at eight major planets orbiting their parent star, our sun. In October, brilliant Venus is seen low in the southwest sky after sunset, while bright Jupiter is seen in the southeast, with dimmer Saturn about five inches to Jupiter’s right at arm’s length.
Once the planets were identified and studied, we thought we were the only solar system in our Milky Way galaxy. Little did we know all that would change in the early 1990s.
The first discovery of an exoplanet (a planet that orbits a star outside the solar system) was in 1992. Three planets are orbiting a pulsar located 2,300 light-years away. (A light-year is the distance that light travels in a vacuum in one of our calendar years, about 9.46 trillion kilometres.) Pulsars are very energetic stars that result from the explosive death of a massive star, called a supernova.
If these three worlds had any life on them before the star blew its top, the shockwave from the supernova stripped away their atmospheres and is bathing the lifeless planets in deadly radiation.
However, the big discovery came in 1995, when the first exoplanet orbiting a sunlike star was discovered. The star, named 51 Pegasi, is located 50.8 light-years away in the constellation Pegasus, which is seen overhead on these cool fall nights.
This star is visible with the unaided eye on a clear, moonless night. Of course, because of its size and distance, you will not see the exoplanet, named Bellerophon, even with a telescope, but knowing that a world is orbiting that tiny point of light is mind-blowing.
The search did not end in 1995. Thanks to ground-based telescopes and the orbiting Kepler space telescope, the count so far is already an amazing 4,531 confirmed planets, with 7,798 more candidates. These discoveries were made from just a small portion of the sky.
Some astronomers have stated that every star in the night sky has at least one exoplanet around it. Many are too close to their star to support life as we know it, but there are a few in the habitable (or "Goldilocks") zone, where water remains liquid, like the oceans here on Earth.
Finding an exoplanet with water is the key to finding life.
The Milky Way contains an estimated 300 billion stars. Imagine if a single grain of table salt represented a star: you could fill a sandbox six meters (20 feet) long by six metres wide by 30 centimetres (one foot) high with salt just representing the stars in our galaxy.
There are an estimated two trillion galaxies in the observable universe. Think of all those worlds and the possibility of life.
Look up at the sky; look at a sky full of planets.
Till next time, clear skies.