In the earliest years of the TV western “Gunsmoke,” do you recall the name of Marshall Dillon’s deputy? Nope, Festus came later. It was Chester (played by Dennis Weaver), and perhaps you’ll remember that Chester walked with a limp, the origin of which I never learned.

Now let’s go much further back to when our 5 billion year-old solar system was young—perhaps no more than several hundred million years old. It’s a good thing we weren’t around yet as the planet that would eventually become our home was whacked by a smaller planet producing a cataclysmic collision that destroyed the other planet and left Earth, like old Chester, with a limp.

Ever since, as Earth orbits the Sun, its North and South Poles aren’t straight up and down but rather are tilted at a 23 1/2 degree angle. And as a result, each hemisphere spends half a year tilted toward the Sun and the other half tilted away. When tilted toward the Sun, its days are longer than its nights, and when tilted away, its nights are longer than its days.

Twice each year Earth reaches a point in its orbit when the hemispheres reverse positions, and one of those times comes March 20th, the first day of spring in the Northern Hemisphere (and fall south of the equator). Called the vernal equinox—Latin for “spring equal night”—it’s the day when for an instant neither pole is tilted toward or away from the Sun, and the day and night are of equal length...at least theoretically.

But a look at sunrise and sunset times shows it’s not so. For my home in Waco, Texas, March 20th sunrise is at 7:32 a.m. and sunset at 7:40 p.m., thus on this day of the “equal night,” day is 8 minutes longer than night. So what’s going on here?

Well, actually two things account for this apparent discrepancy—one a human factor, the other natural.

The first has to do with how we define day and night. Since the Sun has a discernible diameter, in theory day should start when half the Sun has risen and end when half has set. However, by definition, day officially begins the instant the first part of the Sun peaks over the eastern horizon and doesn’t end until the entire Sun sinks below the western horizon, and this adds about 2 minutes to each day.

The second factor, which lengthens day even more, comes from the bending of light called refraction. As the Sun nears the horizon, its light rays are bent upward as they pass through Earth’s atmosphere. Acting like a strategically placed mirror, the atmosphere lets us see a little below the horizon—enough that we can actually see the Sun some 2-3 minutes before it physically rises above the horizon, and 2-3 minutes after it sets.

So just as in George Orwell’s *Animal Farm*, where “some animals are more equal than others,” days are “more equal” than nights, even at the equinox.

Sky Calendar:

• March 10th, Tue.: The full Moon is called Lenten Moon, Sap Moon, Crow Moon, and Worm Moon.
• March 18th, Wed.: The Moon is at 3rd quarter.

* March 22nd, Sun. morning: The crescent Moon is to the upper right of Jupiter low in the east at dawn.

• March 26th, Thurs.: The Moon is new.

•Naked-eye Planets. Evening: Venus, ending its run as the “evening star,” is lost in Sun by month’s end, but Saturn is now at its best all night. Morning: Jupiter and Mars are low in the east at dawn with Saturn the brightest object in the west.

Stargazer appears every other week. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, TX 76707, (254) 753-6920 or paulderrickwaco@aol.com. See the Stargazer Web site at stargazerpaul.com.