These of us courageous souls who inhabit America’s northern climes know that it’s not the chilly that brings on the winter blues. You go to work and it’s darkish. You permit work and it’s darkish. The solar? What’s that?
Certainly, as I put up this at three:30 p.m., the solar is already nearing the horizon. The sky above is darkish. In the present day — the Winter Solstice — the solar will set at four:20 p.m. right here in Milwaukee.
However that’s truly fairly bizarre. It’s the shortest day of the yr, but the solar was setting a number of minutes earlier final week. And the newest dawn received’t occur till January—the precise date varies by latitude.
So why doesn’t the Winter Solstice, the purpose the place the solar seems farthest south within the sky, coincide with the newest dawn and earliest sundown?
We’ll discover the reply by inspecting a collection of imperfections:
- Our planet doesn’t orbit in an ideal circle
- Earth is tilted on its axis
- A day isn’t truly 24 hours lengthy
That final reality is a little bit of a mind-blower, so let’s begin there. My cellular phone would inform me that 24 hours handed between midday at present and midday yesterday. However that’s truly a mean over the course of the yr — not day by day is 24 hours lengthy.
Astronomers use the time period photo voltaic midday to explain when the solar reaches its highest level within the sky for a selected day. And photo voltaic midday can range by a number of minutes. This shift additionally shifts the time our clocks present for dawn and sundown. For instance, a pair weeks in the past, photo voltaic midday occurred at 11:52 native time. And a pair weeks from now, photo voltaic midday will fall later than midday, skewing the sundown later.
Now let’s look at these different two components, as a result of additionally they play a task.
Earth doesn’t orbit in an ideal circle across the solar. We’ve identified that for hundreds of years, so it shouldn’t be a shocker. Nonetheless, on the solstices, when our planet is at its farthest (winter) and closest (summer season) from the solar in its orbit, we sweep out a smaller angle. Meaning the planet has to rotate a bit extra or a bit much less to finish a day. Because of this, the day will get barely longer or shorter, so our clocks fall behind or bounce forward.
Lastly, everybody is aware of that the explanation now we have seasons in any respect is as a result of our planet is tilted off-axis (by 23.5 levels). However Earth’s tilt on its axis finally ends up having one other attention-grabbing impact on the climate. What’s neat is that the northern tilt — coincidentally — traces as much as level away when Earth is closet to the solar. That moderates the climate. After which when the farthest level of our orbit from the solar occurs because the north factors away, it accentuates winter snowfall.
So, since we’ve reached the shortest day of the yr, the times will now progressively get longer and the sunsets later. And earlier than we all know it, I’ll be complaining that there’s simply not sufficient darkish hours within the day to stargaze.