What you see in the sky is not always reality.

There are many illusions up there. Whenever you gaze upon the starry sky, you're not seeing the stars in real time. You're actually gazing into the past in varying degrees.

Everyone knows that the stars we see at night are very far away. Trying to express their distances in miles involves using values in the trillions, and except for the national debt, not a lot of us use trillions all that much.

It's hard to get your mind wrapped around the concept of a trillion of anything. We're talking one thousand billion here!

It's easier to express stellar distance in light-years. A light-year is the distance a beam of light travels in one year's time at the speed of light, which is just over 186,000 miles a second. If you do the calculations, that works out to about six trillion miles for just one light-year.

On average, most stars you see in the heavens with just your naked eye are about 100 light-years, or 600 trillion miles away!

A good example of a star that's 100 light-years away is Alkaid, the star at the end of the handle of the Big Dipper.

Since light travels at a set speed, the next time you see Alkaid you're not seeing it as it is right now but as it was in 1904, when less than 15 percent of American homes had bathtubs!

Many other naked eye stars in the sky are a lot farther than Alkaid. Some stars are thousands of light years away!

One such star is Deneb, the brightest star in Cygnus the Swan, flying high over the evening southwestern sky this time of year. Deneb is about 3,200 light-years away, so we're seeing Deneb as it was around 1800 B.C., long before there even was an America!

One heavenly illusion that comes into play this time of year is the Autumnal Equinox, otherwise known as the first day of fall, which happens to be Monday night.

We've all been taught since grade school that on that day, day and night are equally long, 12 hours for each.

However, if you look in the Butler Eagle this Thursday, you'll see that we actually have 12 hours and 6 minutes of daylight. Where did that extra 6 minutes come from? It's all due to the illusion of astronomical refraction, caused by Earth's atmosphere.

The sun's light is actually bent by our atmosphere, making the sun itself appear higher in the sky than it actually is.

When we see the sun near the horizon, we have to look through a lot more of our Earth's atmospheric shell, and the bending of the sun's light is so extreme that the sun appears to be above the horizon when it's actually below the horizon, giving us the extra few minutes of precious daylight.

Another great illusion is a rising full moon. It's an absolute joy to see as it climbs above the eastern horizon shortly after sunset, even if it wipes out serious stargazing with all the light in the sky.

The sight of that huge moon on the rise is something you don't want to miss.

But why is the moon so huge when it rises?

The truth is that it's not any bigger. It's just another illusion, this one caused by our own eyes. It's simply an optical illusion that we see whenever the moon or sun is close to the horizon, because we're comparing it with objects we see on the landscape.

The moon is no smaller when it's high in the sky. You can prove this by using a paper clip.

When the moon is first rising, hold out a paper clip at arm's length and bend it apart so that the moon's disk fits exactly between the two ends of the clip.

A couple of hours later, when the moon seems smaller, hold out that same bent apart paper clip at arm's length to measure the moon again and you'll see that it's exactly the same size.

Try it, it really works!

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, "Pennsylvania Starwatch," available at bookstores and at his Web site www.lynchandthestars.com.