The 2016 Butler version of the full harvest moon is coming Friday night, but for all practical purposes it will be full on Thursday evening as well.

As the moon orbits the Earth the angle between the Sun, the Earth, and the Moon opens up to 180 degrees. In other words, all three celestial bodies are in nearly a straight line.

The Earth is in the middle between the distant sun and our lunar neighbor. That means that the side of the moon facing the Earth is completely lit up by the sun.

It also means that the moon rises at sunset, and sets at sunrise.

Weather permitting, every 29.5 days we get to enjoy a full moon, but what makes the harvest full moon special is that it seems to hang around a little longer.

Usually you only notice a full moon for two or three evenings because it rises so much later from night to night. Because of the moon’s orbit around the Earth the moon is constantly moving eastward among the backdrop of distant stars.

The moon migrates 13 degrees every 24 hours, so it rises about 30 to 60 minutes later from night to night.

What makes the harvest moon unique is that it rises only about 20 minutes later each night, so the full moon seems to hang around a few more nights than usual.

This happens to the full moon closest to the autumnal equinox, which is Sept. 22.

The exact details of why this happens get a little hairy, but it basically has to do with the fact that the full moon this time of year rises directly in the east, and sets directly in the west.

It also has to do with the narrow angle of the ecliptic with respect to the horizon. All that happens around the autumnal equinox.

A full moon or near full moon does a number on serious stargazing as the skies get whitewashed, even in the countryside.

All but the brightest stars and constellations fade out. It’s also a terrible time to gaze at celestial treasures with any size telescope because nebula, galaxies, and other targets get lost in the moon’s glow.

It’s not even all that great aiming your scope at the moon itself because of all the direct sunshine bombarding it.

The best place to look at the moon is the line between the sunlit side of the moon and darkened part of the lunar surface.

That line is called the terminator, and that’s where you can really get a great look at mountain tops and crater walls because of the low sun angle creating all the shadows.

When you have a full moon or a near full moon, there’s little or no terminal.

Looking at a full moon with a telescope won’t make you loonie, but it can make your eyes sting.

In fact, at my stargazing classes I advise people to actually put on sunglasses before they look at the full moon through their telescope. You can actually get filters for telescope eyepieces that act like sunglasses.

A rising harvest moon usually has a bright orange color to it, and that orange hue hangs around longer into the evening than it does with a regular full moon.

That’s because the harvest moon rises at a lower angle with respect to the horizon, so the moon hangs lower in the sky longer.

Whenever you view the sun, moon, or any astronomical objects close to the horizon, you’re looking through a lot more of Earth’s atmosphere.

The dust and moisture scatters away all but the reddish orange components of the moon’s light. That effect usually goes away gradually within an hour, although if there’s a lot of pollution in the air the red and orange colors hang on for much longer.

Another thing you’ll notice is that the moon appears gigantic when it first rises, but shrinks after an hour or so. This is a complete optical illusion.

The moon just seems bigger when it first rises because you’re comparing it with land objects — trees, buildings, strip malls, or whatever.

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 the 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.

There’s another way to take away the optical illusion of the giant moon as it rises, although I doubt you’d want to try. You turn your back to the rising moon, bend forward and watch the rising moon between your legs. The harvest moon will be smaller, but you’ll probably wind up in traction.

Mooning the moon is painful.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis. He is author of “Stars: A Month by Month Tour of the Constellations” published by Adventure Publications. It is available at bookstores and at www.adventurepublications.net.