Sky watch: Finding the 7th planet, Uranus

How many planets does our solar system have? Back about 230 years ago, when life was much simpler, every astronomer and schoolchild knew the answer. There were six planets: Mercury, Venus, Earth, Mars, Jupiter and Saturn, five of which wandered the starry heavens from night to night. And that's all that were ever known since the dawn of time.

That's why, in 1781, the world was stunned when musical composer and amateur astronomer William Herschel announced his discovery of a seventh planet. It was named Uranus, after the father of the Titans and grandfather of Jupiter in Greek mythology.

What's most intriguing about Uranus is that it wasn't found earlier -- much earlier -- for, you see, the planet can sometimes be spotted with the naked eye. In fact, right now is one of those times, and if you've never seen our seventh planet, now is a great opportunity to begin your search.

Uranus reaches its opposition -- the point in its orbit where it lies closest to Earth -- on Monday, and for the next week or so will rise in the east not long after sunset. After the moon sets this week, look midway up in the eastern sky for the Great Square of Pegasus. Below and to its right appears an oval pattern of faint stars that outlines one of the fish of Pisces. Uranus lies about ten degrees below that, in a region that appears as being relatively devoid of stars.

Aim binoculars in this direction and you may spot Uranus as a dim point of light whose unique bluish-green hue and steady glow distinguish it from neighboring stars. Through a small telescope, the planet appears as a distinct, though tiny, blue-green disk.

Once you know Uranus and can identify the stars around it, try searching for it with your eyes alone. If you have a clear, dark rural sky far from city light, you may be surprised by how easy this is!Now, if Uranus is this simple to spot with the unaided eye, why hadn't the ancients done so? And if they had, how might that have changed history?

After all, the five visible planets (plus the sun and the moon) lent importance to the number seven, and we see it everywhere: There are seven days of the week, seven rungs of perfection, seven emblems of the Buddha, the seven gates of Thebes, seven wonders, and on and on.

So it's natural to wonder how things might be different had there been eight -- instead of seven -- significant bodies that traveled the heavens. It's only by chance that there aren't.

Just a little something to ponder as you're gazing skyward this week!