It’s autumn, the season of change! Trees are turning to brilliant colors, marking the time for hot cocoa and warm coats. The long days of summer are past us, and each day will be shorter than the last. But… why does this happen? Why are days getting shorter in the autumn (and winter), as opposed to the summer? Turns out, it’s all about the Earth’s axis and its path around the sun.

It’s worth noting that people in the northern and southern hemispheres experience opposite trends. Those living in the northern hemisphere experience longer days and shorter nights in the summer and the opposite in winter — while for those in the southern hemisphere, the exact opposite is happening. This isn’t a random phenomenon, there’s a specific reason behind it. It happens because the Earth’s axis isn’t perpendicular (straight down at a 90-degree angle) to its orbit, but it’s instead tilted just a bit.

So, as the planet orbits the sun every 365.25 days, sometimes the Northern hemisphere is closer to the sun (summer) while sometimes it is farther away (winter). To explain why days are longer in summer and shorter in winter, let’s first take a look at the two ways our planet is rotating all the time and the consequences behind it.

The Earth spins around its axis, or the imaginary line running through the North and South poles, every 24 hours. This means that at any given moment, one part of the planet is facing the sun and experiencing daytime, while the opposite side is not, and experiences nighttime. The Earth also orbits the sun, completing a revolution every 365.25 days.

Now, imagine a plane that connects the middle of the sun and of the Earth. If the axis of the planet was straight up and down at 90 degrees to this plane, the length of time each hemisphere spent facing the sun would always equal the length of time facing away. But this isn’t the case. Instead, the axis is tilted slightly, at 23.5 degrees to be exact.

This tilt is always pointed in the same direction in space, toward Polaris (the so-called North Star), even as the planet travels in a circle around the sun. This translates into the Northern hemisphere being closer to the sun (summer) or farther away (winter) throughout Earth’s yearly orbit.

Depending on where you are on the planet, the difference in the length of the day from season to season can be larger or smaller. That’s also related to latitude, which says how far a point on a planet is in relation to the equator.

Higher latitudes are closer to the poles, while 0 degrees in latitude is the equator itself. But as the Earth is a sphere, the higher latitudes near the poles are already curving away from the Sun and therefore receiving less sunlight every 24 hours. That’s the reason for the poles staying colder than the rest of the planet. With an extra 23.5-degree tilt away from the Sun, a pole receives less light and will only experience a short window of daytime.

Equinox and solstice

Equinoxes and solstices are not only key dates in the calendar but also in the journey of Earth around the Sun.

They are used to outline the transitional periods between the seasons — when winter changes to spring, summer to autumn, and so on. How long days and nights are will depend on the position of the Sun in the relation to the Earth.

The equinox happens twice a year and marks the when the amount of day-time we get is equal to the amount of night time we get — the day is equal to the night. This takes place when the sun is positioned right above the equator. It happens usually around the 20th of March, which is the spring equinox, and again around the 22nd of September, known as the autumn equinox.

The word equinox actually comes from two Latin words, “equi-” which means equal and “nox” meaning night. So, from the day of the spring equinox, the day is longer than the night and from the day of the autumn equinox, the night becomes longer than the day.

The equinox, by definition, falls on the day when the center of the sun is at the horizon, and both day and night last 12 hours each. However, the top edge of the sun (not its center) is visible first on sunrise. In spring, this means that the time when day and night are actually equal comes before the equinox — it’s known as the equilux, from the Latin word “lux” meaning light.

Meanwhile, the solstice also takes place twice a year. There’s a summer solstice around the 21 June in the Northern Hemisphere and a winter solstice around the 21 December. During the summer solstice, the Northern hemisphere experiences its longest period of daylight in a year. During the winter solstice, it sees the longest night of the year. So while the equinox marks the date when the day and night are equal, the solstice marks the biggest difference between the day and the night.

The sun is at its highest point in the sky in the middle of the day during the summer solstice. This is reversed during the winter solstice — at noon the sun is at its lowest of the year.

In northern areas this change is extreme, and some areas can experience continuous daylight (or night time) for months.

Every September, the Northern hemisphere officialy enters autumn, and from that point on, each day has one less minute of daylight, culminating in the winter solstice. It might not seem like a lot, but over the course of a month it adds up to half-hour of lost daytime. Then, as in most of the US, you might be setting your clocks back an hour for the end of daylight savings time.

Dealing with shorter days

Understanding why days are shorter in autumn is one thing, but another thing is dealing with its practical consequences. It’s not an easy task, the changing day length has marked effects on your physical and mental health. We get long stretches of daylight and late sunsets during the summer, but all that is set to change. Adjusting can be tough, but there are ways to make it easier.

• Exercise. There’s nothing that boosts the mood like endorphins. It’s the first line of defense against seasonal and clinal depression. Doing any sort of exercise can work wonders for your disposition. If you want to make the most of the daylight, the best bet is to find time for an outdoor workout during your lunch hour or early in the morning.
• Go to bed early and set up a routine. If you are going to wake up early to exercise you should discipline yourself to an earlier bedtime. Even if you’re not planning to wake up early for a workout, getting enough sleep is always important to keep you in a good mood and healthy mental state, but even more so in the winter with less sunlight.
• Plan a holiday once in a while. It might be good to get some summer somewhere south of the equator. If you need more sunlight, then plan a beach holiday for the darkest time of the year. Chilly places don’t necessarily mean dark places. You could plan a ski or snowboarding holiday out West in Colorado or Utah and still have to pack your sunscreen.
• Get outside, even when it’s cold. There’s no such thing as cold weather, only weather for which you haven’t dressed appropriately. You can still have lunch in the park or a morning run, even if it’s cold. Or even spend an evening with friends. We might feel like entering hibernation if it’s too cold, but that doesn’t have to be the case — we can still keep ourselves active throughout.