By the time you read this article, spring will already have started. Officially. I looked it up. Several sources listed the start of spring, 2019, as Wednesday, March 20, at 5:58 p.m. This is the moment of the vernal equinox, when the sun passes directly over the equator. More precisely, it is the moment the center of the sun touches the imaginary plane passing through the earth’s equator. It is such a precise definition that the start of spring has been calculated not just to the day or hour or minute, but even to the second. (Perhaps even to the millisecond, though I didn’t find any sources claiming that.)
Yet to have such an exact definition, we need to know the exact center of both the sun and the earth. Here I will risk exposing my lack of knowledge to my astronomer and geologist friends (and hope none of them are reading this): How do we know the exact center of either? The earth is not a perfect sphere. The sun, though it might approximate a sphere at any given moment, is not even a solid object. In fact, though that “exact” moment when spring begins can been calculated to the second, according to one source there are two different ways of calculating, and they lead to two different answers. Granted that the two answers aren’t days or hours apart, but they can be more than a minute apart.
Then there is this: the word equinox comes from Latin and means “equality of night,” which means equality of night with day, when the length of day exactly equals length of night. Except the equinox doesn’t actually happen on the equinox. By the time spring officially began on March 20, Vermont already had about 10 minutes more daytime than nighttime. Unlike the equinox, sunrise and sunset are not defined by when the center of the sun touches the horizon, but by when the first (and last) edge of the sun’s disk appear (and disappear). And the sun is big. The sun’s edge touches the horizon a couple minutes before its center.
All of which suggests that we need a better definition of spring. Though students may feel that spring begins on a Friday afternoon at the start of spring break, those who spend time in the outdoors know there is a more precise and important definition. I used to think spring began when the first robins appeared in my lawn. Robins are the iconic harbingers of the end of winter. And then, to my dismay, I learned in my adulthood that robins actually stick around all winter. I just never remembered seeing them as a child, perhaps because I wasn’t looking. No. It isn’t robins. But it is another bird. Spring begins the precise moment when you hear the first flock of Canada geese winging their way north. (More than a week ago, my wife announced she had heard them.)
Not all scientists agree on this calculation, however. As with the astronomical calculation, there are a few other formulas that can be used. Spring actually begins when you drive past a meadow that has just been cleared of snow, and see a herd of 15 whitetail deer browsing together (still wearing their dark winter coats.) Last weekend I caught sight of two such herds in the span of an hour, off Quarry Road in Middlebury and River Road in New Haven. 
Except I haven’t planted my lettuce or edible pod peas yet. And strong scientific arguments can be made that spring begins when the garden soil can be turned and the first garden seeds can go into the ground. Or does it have to do with the precise middle of sugaring season: the exact second between when the first drip pings in the bottom of the sap bucket and when the last dark drop trickles off the end of the tap? Some may be tempted to think that spring begins the day after Rikert closes for the season. But we know that isn’t correct, since “spring skiing” exists.
When my family lived in Maine in the late 1960s, the average day the ice went off the lake was the last Saturday of April. As climate change has impacted New England over the past half century, that average has slowly shifted two weeks earlier, even as the ice now forms in the fall a full two weeks later. The day of ice-out on the lake is a reasonable definition of the start of spring. (My brother tells me it won’t be until the start of May this year.)
Speaking of spring break, a national fly fishing magazine booked me to do a story on a steelhead river in Oregon I have fished many times. I need to head out there during spring break and get some photos — ideally of me catching some big steelhead. Oregon has been very dry, and I’ve been worried that the river will be too low. I’ve been following the weather, hoping for rain. The temperature has been 70 degrees this week. In preparation for the trip, I drove over the Crown Point Bridge a week and a half ago, hoping to catch some spring steelhead on a New York tributary of Champlain. I was overly optimistic. The pools were still covered with ice and snow. Just to get into the river near one of the few open patches of water, I had to crawl over a sheet of ice. Once in the river, I could only fish about 60 yards upstream before my way was blocked. Spring definitely had not hit New York.
Then it dawned on me. Spring does indeed have a very precise definitely. In Vermont, it starts 30 minutes before sunrise on the second Saturday of April when trout season begins.