Everybody knows the universe is a big place.
What’s hard to grasp is how big.
A few years ago I bought my wife a telescope for Christmas, figuring she could check out the moon and a few planets and get a fix on a star or two and help fill in some of the gaping holes in our understanding of what’s around us. Not a bad plan, but I neglected to factor in the dozens of trees that surround our house and make it impossible to look out a window without seeing branches. Try as we might, we couldn’t get a clear shot of the sky, and neither of us felt like standing around outside at night in below-zero temps trying to dispel our ignorance.
As it turned out, we put the telescope away until spring, and in the meantime started reading the booklet that came with it. We found that the more we read, the bigger the universe got.
For example: on page five we learned that after hundreds of years of study, astronomers around the world agree that the Sun is an ordinary star in what might look like a gigantic saucer-shaped star system. This gargantuan star system is called a galaxy. Our galaxy, called the Milky Way Galaxy or The Home Galaxy, is almost too big to think about. It contains at least 100 billion stars, plus a lot of gas (mostly hydrogen), dust (mostly iron and carbon), and lots of energy.
So how big is a star? We know from grade-school days that Earth is a little less than 8,000 miles in diameter. Stars, we find, range in size from 100,000 miles to hundreds of millions of miles in diameter. And there are hundreds of billions of them!
Unable to grasp the dimensions these numbers represent, we retreat back to our booklet for help. On page nine, under the heading “Separation of Objects,” various distances are listed. Light, we remember, travels at a speed of 186,000 miles per second. Our list calls this Photon Travel Time. We plunge in.
The first entry is Earth to Communication Satellites, the kind that relay TV and telephone signals. The distance is 22,300 miles. Photon Travel Time: 1/10th of a second, or about an eye blink.
Earth to Moon: 250,000 miles. Travel time: one and a half seconds.
Earth to Mars at its closest point: 40,000,000 miles. Time: 215 seconds, or roughly four minutes.
Earth to the Sun, about 93,000,000 miles; 500 seconds, or eight and a third minutes.
Earth to Pluto (roughly 3.6 billion miles), 322 minutes, or about 5.4 hours.
Heads spinning, we skip down the list to Vega, the brightest star in the summer sky. Distance: 156 trillion miles. Photon travel time: 26 years.
Earth to Mizar, a bright double star in the handle of the Big Dipper—444 trillion miles away. Time: 75 years, nearly an average American life span! Unless you’re that old or older, the light you are seeing left the star and started streaming earthward before you were born.
Finally we skip to the last entry on the list. Earth to the Andromeda Galaxy (one of the ten-billion-plus other galaxies in the universe). Distance: about 14 thousand, thousand, trillion miles. Time: 2.4 million years. The light we are seeing when we look at the Andromeda Galaxy left there before there were human beings on planet Earth.
The universe is a big place.