This year's harvest moon, which is the first full moon closest to the date of the autumnal equinox, will occur at 4:19 a.m. Thursday, only six hours after the exact time of the equinox.

Despite the fact it messes up my stargazing and new love of astrophotography, I can't help but love watching the full moon, even though it hogs up the Butler night sky and gives all but the brightest stars and celestial treasures a lunar whitewashing.

By far my favorite full moon is the "harvest full moon," which will officially take place at 4:19 a.m. Thursday. In reality, though, the moon will be more or less "full" from Tuesday evening through Saturday evening.

Astronomically speaking, it's called a harvest moon because it's the closest full moon to the date of the autumnal equinox, when autumn officially begins. That's when the sun, on its annual path among the background stars called the ecliptic, slips below the celestial equator in the sky, which is a projection in the heavens of the Earth's terrestrial equator. That simply means from now until the first day of winter in late December the sun's daily path will take a lower and lower track in our sky, bringing on colder and colder weather — oh goody!

Anyway, this year the exact time of the full moon this month is only six hours after the exact time of the autumnal equinox, which will take place at 10:09 p.m. Wednesday. That makes the exact time of the full moon this month and the exact time of the autumnal equinox the closest they've been to each other since 1991, and the closest they'll be again until 2029. That's why I say this year we really have a harvest moon with an attitude.

In truth, though, the 2010 edition of the harvest moon isn't all that different from any other harvest moon. What makes the harvest moon special for observing is the unique celestial mechanics of this time of the year.

Every night, the moon migrates eastward among the stars as it orbits around Earth. That causes our lunar neighbor to rise about 40 to 60 minutes later from night to night. During the time around the harvest moon, the moon rises only 20 minutes later each night. The exact details of why this happens get a little hairy, but it has to do with the angle of the ecliptic, the sun's path among the stars, and where it intersects the horizon. We'll just leave it at that.

No matter what time of year it is, one of the great things about watching a full moon rise is the absolutely stunning orange hue to it. Sometimes when you first glance its way, you might think, as I have, a fire has broken out in the distance until you come to your complete visual sense and recognize it for what it is.

The orange hue of a rising or setting moon or sun is caused by our atmosphere. The white light we see from the moon when it's high in the sky is just reflected sunlight and is actually a conglomeration of all the colors in the rainbow, otherwise more formally known as the visible part of the electromagnetic spectrum. When the moon is close to the horizon, as it is when it's rising, the light is filtered through a lot more of the shell of Earth's atmosphere than when it's higher in the sky. That thicker atmosphere close to the horizon scatters away all but the orange-red component of the moon's light, giving it the fiery or pumpkin color.

The gigantic size of that orange moon when it first rises is a complete optical illusion! The moon just seems bigger when it first rises because you're comparing it with land objects such as trees, buildings and strip malls. It's the same size whether it's high or low in the sky.

You can prove this to yourself with a pencil. When you first see the moon above the horizon, hold the eraser end of the pencil at arm's length against the rising moon. Compare the size of moon with the eraser head. Then, about two hours later when the moon seems smaller, hold that same pencil at arm's length up against the moon and you'll see that the moon is no smaller compared to the diameter of the eraser. Try this. It really works.

If you really want to take away the optical illusion of the giant moon as it rises, although I'm not sure why you would, just bend forward and watch the rising moon between your legs. The harvest moon will be a smaller, humbler sight, and you might also get to spend some quality time with a local chiropractor. In a way, you're mooning the moon!

By the way, this Wednesday night, there's an extremely bright "star" just below the full moon. However, that's actually the planet Jupiter, at its closest point to Earth in 2010. I'll tell you more about the Goliath of our solar system next week in Starwatch.

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 website www.lynchandthestars.com.