Do you recall the name of Marshal Dillon’s deputy from the earliest years of the TV western “Gunsmoke”? 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 farther 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 are instead 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 a hemisphere is 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 was Friday, 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, Friday’s sunrise was 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 the 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. 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 to 3 minutes before it physically rises above the horizon, and we see it 2 to 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.

* Next two weeks — Average sunrise: 7:22 a.m.; average sunset: 7:45 p.m. Sunday morning the crescent moon will be to the upper right of Jupiter, low in the east at dawn. The moon will be new Thursday.

The evening of March 29, the crescent moon will be below the Pleiades star cluster, low in the west at dark, and above the cluster next evening. The moon will be at first quarter April 2.

* Naked-eye planets — Venus, now setting in the west soon after sunset, will pass between the sun and Earth on Friday and emerge in the morning sky in April.

Saturn is now at its best all night — in the east in the evening and in the west in the morning. Jupiter rises in the east before dawn while Mars rises as dawn is breaking.

* Star party — The Central Texas Astronomical Society’s free monthly star party is tonight at the Waco Wetlands beginning at 8, weather permitting. For directions, see my Web site.

Stargazer appears every other Saturday in the Brazos Living section. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at (254) 753-6920 or at paulderrickwaco@aol.com.