Scheckel
QUESTION: How big is our galaxy?
ANSWER: Very big!! The Milky Way Galaxy is one of billions of galaxies in the known universe. The Milky Way is a spiral galaxy in what is called the Local Group within the Virgo Supercluster. The disk of the Milky Way Galaxy is about 100,000 light years in diameter. It is estimated that our Milky Way Galaxy contains about 200 to 400 billion stars.
Our solar system, with the sun as the primary star, is about two-thirds of the way out in one of the spiral arms of the Milky Way. If the entire galaxy were reduced to 80 miles in diameter, our solar system would be only 0.1 inches in diameter. Indeed, we are small stuff in a big place!!
The term “light year” is used above. A light year is a unit of distance, not a unit of time. It is the distance that light travels in one year. Light travels at about 186,000 miles a second. So, multiply the number of seconds in a year, roughly 31.5 million, by 186,000 miles per second, and a light year comes out to be about 6 trillion miles. That is six million million miles, or written out as 6,000,000,000,000 miles.
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Go out in the country, away from the city lights, look up, and note the hazy band of white light running from the southwest to the northeast. You are looking edgewise in the heart of the Milky Way. The Milky Way appears brightest in the direction of Sagittarius, which is toward the galaxy’s center.
Be aware that every star you see with the naked eye in the night sky is in our own Milky Way Galaxy. There is one exception. The Andromeda Galaxy in the constellation Andromeda appears as a white, fuzzy patch of cotton candy. The Andromeda Galaxy, known as M31, can be seen right off the square of Pegasus. Use any star chart or the internet to find its position.
The Andromeda Galaxy is one of about 50 galaxies in the Local Group and is a barred spiral galaxy like our own Milky Way. It is about 2.5 million light years away. When you look up at the Andromeda Galaxy, the light you see tonight left the galaxy 2.5 million years ago. We don’t know what it looks like today or if it is even still there. All we know is what it looked light 2.5 million years ago. We are looking back in time. Quite humbling!
The Milky Way’s center is home to a very dense object believed to a super massive black hole. Most every observed galaxy has one or two. There is an ad running on television that says the universe has more stars in it than there are grains of sand on the Earth. Best estimates: There are one hundred stars for every grain of sand on Earth.
Sources: NASA, SpaceNews.
Larry Scheckel taught science at Tomah High School for 38 years and was named Tomah Teacher of the Year three times. Send comments and questions to [email protected].
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