The U.S. Capitol building is illuminated before sunrise in Washington, D.C. (Andrew Harrer/Bloomberg)

At 5:44 a.m. Wednesday, comes one of the great signs of stability, certainty and permanence provided to all of us in a world of change. That early morning moment is the time in Washington of the winter solstice.

The solstice, the time each year when the sun reaches its lowest point in the sky, is generally regarded as the moment when winter begins. That is understandable because, after all, the sun has so great an effect on creating the seasons.

The solstice, in its dependence on the position of the sun, is said to start the “astronomical winter.” Why not? Everything must start sometime.

On the other hand, meteorologists consider Dec.1 to be the start of winter. Also, we here in Washington have had more than a taste of wintry weather already.

In addition, it should be noted that Tuesday’s high temperature in Washington was 37 degrees. By contrast, the National Weather Service predicted that Wednesday’s highs will be about 10 degrees warmer.

That suggests the difficulty in citing daily thermometer readings to support the idea that the solstice divides autumn from winter. It’s a fuzzy boundary at best.

Yet one clear and important effect of the solstice on life in Washington ought not be overlooked. It is the effect on the length of our days and nights.

As many have noticed, the days have been getting shorter and shorter here, and in the rest of the northern hemisphere, for months. There has been less and less daylight, more and more darkness.

The amount of daylight here has declined until Wednesday the time between sunrise and sunset has shrunk to nine hours, 26 minutes and 17 seconds. (According to the website.)

But that is going to stop. That shrinking amount of sunshine does not go on without end. The decline in the length of days, perhaps wondrously and marvelously, stops with the solstice.

That endows the moment of the solstice with great significance and meaning for all of us.

Even after Wednesday, and 5:44 a.m. Eastern Standard Time, the moment of the solstice, days will still be short. Nights will still be long. But the important thing is that those long nights will not get longer. The encroachment of the hours of darkness has been halted.

Over a year, the change in the position of the sun in the sky is cyclical. We have reached one of the extreme points in the cycle.That is the meaning of the solstice. Now it is time to move in the opposite direction.

Days will not continue to get shorter, and they will soon begin to get longer. The change will be scarcely noticeable at first. But it will happen, an assertion that can be made on the basis of the predictability of celestial mechanics and by appeal to scientific knowledge about the geometry of the earth’s orbit.

Inauguration Day, Jan. 20, about a month from now, will be about 27 minutes longer than the day of the solstice.

The axis of the earth is tilted. As the earth revolves around the sun, the tilt of the earth’s axis remains the same. But on part of yearly orbit, the tilt is toward the sun, and on the other part it is away .

When it is winter in Washington, the northern hemisphere is tilted away from the sun. In summer the opposite is true.

At the moment of the winter solstice, the tilt away from the sun is as great as it gets. The result of the tilt is to make it appear that the sun has sunk in the sky.

But increasingly now, that tilt will be less away from the sun, and more toward it, a little more each day. That will go on for six months, until in June the earth’s axis will be tilted as far toward the sun as it goes, as it has gone year after year, decade after decade, century after century.

It is repetitious, but it is also in its way reassuring. It is predictable, and predictability is in its way comforting, even if winter often brings days that many people find too cold, and summer brings times that are considered too hot.

It might also be noted that the time of the solstice is well before the time of sunrise here. But it is not required that we here at our particular spot in the northern hemisphere should see the sun at its lowest point in the sky to know that it has reached that point. And that it will begin henceforward to climb higher.