DARK SKIES: Our galaxy is just one in a billion
OUR Milky Way galaxy is just one of billions of galaxies in the universe, and astronomers are continually searching for more.
By most standards, our home galaxy is 100,000 light years in diameter. With a central bulge of 22,000 LY, the galaxy tapers out to 3600 LY at its edges, where our solar system resides.
Within the galaxy lie stars, billions of them. Some are quite a lot smaller than our sun and some are quite huge. For instance, if our sun was the size of a golf ball, the red giant star Betelgeuse in Orion and Antares in Scorpio would be hundreds of times larger.
Thanks to the Hubble Space Telescope, astronomers have found stars hundreds of times larger. One such star is UY Scuti. If it replaced our sun, its diameter would fill the orbit of Jupiter.
In 2021 when the new James Webb Telescope is launched to replace the Hubble, its six-metre gold-plated mirror will look tens of billions of years further back in time than the Hubble.
Its new discoveries will be made known soon after its launch. Within all galaxies lie hundreds of molecular gas clouds called nebula - the birth place of stars. While no one will ever see a star form - it takes a million years for a star to grow from an embryonic ember to a full grown star - astronomers have recorded, from time to time, a supernova (exploding star) in other galaxies.
If there is to be a supernova in our galaxy it has to be the red supergiant star Betelgeuse in Orion, 1600 LY away. When this star pops, it will be so bright it will be seen in daylight.
So could there be any other solar systems in the galaxy like ours? Why should we believe we are the only one in existence?
Over the past 10 years, astronomers using the Hubble Space Telescope and the Kepler planet-finding space telescope have found and identified thousands of stars, all within a radii of 50 light years from the sun, all with a Jupiter-size planet orbiting a star that in some cases defies the physics of planetary motion and gravity.
The fastest thing we know is light speed and, in a vacuum, a particle of light called a photon travels at 300,000km per second.
At that speed, it would take 4.3 years to reach the sun's nearest neighbour, Alpha Centauri, and 75,000 years to reach the other side of our galaxy. Beyond that is the cold, blackness of space where time and dimension, as we know it, do not exist. The nearest galaxy like ours is the Andromeda galaxy - 2.2 million LY away and best seen in the northern hemisphere.
Within that disc of dust and billions of stars, there would be many other solar systems, many of which could have Earth-like planets and possible life forms.
But until we can prove this, the jury is still out.