Week of Oct. 18-24, 2015

Stand outside on a clear dark night and peer into a sky full of stars. Each of these is like the sun, we say, but how true is that?

Well, all are thermonuclear furnaces. In most cases, the cores of these stars are packed with hydrogen atoms that, under unimaginably high temperatures and pressures, slam into one another, fuse together and create helium atoms. In this process, they release a tremendous amount of energy — some of which prevents the star from collapsing upon itself, some of which leaks out into space as light and heat.

In this way, stars and our sun are similar, but in another they're quite different. To illustrate this for yourself, try a thought experiment, or "Gedankenexperiment," as Einstein used to call it.

Imagine how our brilliant sun's appearance would change if we could drag it farther away. As it recedes, it would seem to become smaller and dimmer ... smaller and dimmer ... until eventually it would look much like the stars we see at night.

Just how far is that? The answer is many trillions of miles.

Suppose you wanted to see how the sun would look against the other stars of the night sky? Well, you can't, of course, but you can see a star just like the sun. Its name is Eta Cassiopeiae, and it lies within the "W" shaped star grouping now high in the northeastern sky after dark. But if your sky is lit by lights of a city, then you may not even be able to spot it.

Eta Cass, as astronomers know it, lies a mere 114 trillion miles — or about 19 light years — from us. Considering that our Milky Way galaxy spans about 100,000 light years, this is a very close neighbor. If it were much farther, we could never see it with the unaided eye.

So why is it so faint compared to most of the other stars in our night sky? Fact is, those other stars are either larger or more luminous (or both) than our sun.

Take Altair, for example, the southernmost bright star in the large Summer Triangle high in the western sky after dark. It's "only" 100 trillion miles away and its light takes 17 years to reach us (we say it's 17 light years distant). It's nearly twice as large and 11 times more luminous than our sun.

And what about Deneb, on the northeastern-most corner of the Summer Triangle? It lies some 9,000 trillion miles, or 1,425 light years, from us. This is a true supergiant with a diameter 108 times greater, and a luminosity more than 54,000 times, that of our sun.

In fact, virtually all the stars we see at night are larger and more luminous than our sun. That doesn't mean there aren't a lot of sun-like stars out there, there are plenty. But much like looking around a sandy beach, we easily see the largest rocks and boulders strewn about, not the millions of grains of sand that make up the beach.

So the next time you gaze skyward on a clear dark night marveling at all the suns you see, think about all those you don't see.

Visit Dennis Mammana at www.dennismammana.com. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.