The Milky Way galaxy is home sweet home to you, me, and about 400 billion stars and 50 billion planets, including Earth. About 500 million of these planets may be in the so-called habitable zone, the distance from a star where an earth-like planet could be just the right temperature to maintain liquid water and support some form of life. With a little under seven billion people and hundreds of billions of animals here on Earth, countless other life forms may also call the Milky Way home.
Our galaxy, visible on clear dark nights as an arc of hazy light across the sky, was formed about 400 million years after The Big Bang, or about 13.6 billion years ago. In Greek mythology it was created from milk spilled by the goddess Hera while nursing Heracles, but we now know it to be a disk-like region of space about 100,000 light years in diameter, comprised of gas, dust and stars gathered together under the influence of gravity. At its center is a supermassive black hole. The Milky Way is a barred spiral galaxy, meaning it has a central bar-shaped structure surrounded by four spiral arms of gas, dust and stars. About 4.6 billion years ago, about half way from the center, on the inner edge of one spiral arm, gas and dust left over from burned out stars collapsed under gravity and ignited to form a new star, our Sun. Of course, from Earth, we can’t see the spiral shape of our galaxy but we know what it would look like, based on observations of other spiral galaxies through telescopes. The hazy band of light we observe originates from stars concentrated within the galaxy’s disk or plane.
The Milky Way spins at about 500,000 miles per hour. An object moving at this speed could travel from the Earth to the Moon and back in one hour. While this may seem incredibly fast, because the galaxy is so immense, it takes our Solar System about 225 to 250 million years to complete one orbit of The Milky Way, or one galactic year. This means that since the birth of the Sun, it has completed only 20 to 25 orbits. Compare that to Earth’s 4 billion orbits around the Sun!
Our home galaxy is part of a cluster of galaxies called the Local Group which in turn is part of the Virgo Supercluster. While The Milky Way may seem vast, it is just one of about 100 billion galaxies in the observable universe. From our perch here on Earth, a humbling thought!
Join the Springfield STARS Club on Tuesday, April 26th at 7:30pm at the Springfield Science Museum for a talk by astronomer Glenn Chaple on The Large Eyes of Small Telescopes. A high school science teacher for 30 years, Chaple wrote for Deep Sky magazine, and for Odyssey, an astronomy magazine for children. He writes a monthly column for Astronomy magazine and is the author of books on astronomy. His latest is Guide to the Universe: Outer Planets. Refreshments will be served, and the public is welcome free of charge.
Copyright © Amanda Jermyn