One of the most surprising facts that most people learn about astronomy during their lives is that the sun we enjoy during the daytime is itself a star, and the stars we see at night are suns.
Amazing, but true!
Of course, stars come in all flavors. They vary in size, temperature, color and brightness.
Our sun, for example, is a rather small and cool white star. It appears large, hot and bright because it’s relatively nearby. It is, after all, “only” 93 million miles away.
Despite their differences, stars all function the same. Each is a thermonuclear furnace inside of which hydrogen atoms under unimaginably high temperatures and pressures slam into one another and fuse to create helium atoms.
This process releases an enormous amount of energy — some of which prevents the star from collapsing upon itself, and some of which pours outward as light and heat.
Despite being a relatively small and cool star, our sun’s nearness makes it appear hot and bright.
But did you ever wonder how our sun might look if it were at the distance of the nearest stars?
To illustrate this, let’s perform what Albert Einstein called a “gedankenexperiment” — a thought experiment.
Imagine how our brilliant sun’s appearance would change if we could drag it farther away. As it recedes, it would appear to become smaller and fainter … smaller and fainter … until eventually it would look much like the stars we see at night.
And just how far would that be? The answer is many trillions of miles.
Of course, this is not possible, but we can see stars in the night sky that are similar to the sun.
One appears within the W-shaped star grouping known as Cassiopeiae, which lies midway up in the northeastern sky after dark. Look for it between the stars Schedar and Navi (see the above illustration).
It’s named Eta Cassiopeiae.
Eta Cass, as astronomers affectionately know it, is a sunlike star that lies 114 trillion miles — or about 19.3 light years — from us.
Considering that our Milky Way galaxy spans at least 100,000 lightyears, this is a very close neighbor indeed. If this star were much farther, we could never see it with the unaided eye.
Why it appears so faint compared to the other stars in Cassiopeiae is because, like the sun, it’s a rather small, cool and dim star.
Compare it with the two stars appearing closest to Eta.
Schedar, to its upper right, is almost 45 times larger, and 734 times more luminous, than our sun. That means we can see it at its distance of some 1,340 trillion miles (228 lightyears).
And what about Navi to its lower left? This star has a diameter about 10 times greater, and a luminosity more than 34,000 times, than that of our sun; that makes it visible at a distance of 3,233 trillion miles (550 lightyears).
The next time you gaze skyward, be sure to check out Eta Cass and imagine that you’re viewing our sun from a great distance.
I think you’ll find it remarkable to realize just how small and faint our sun really is!
