This week the sunsets are at their earliest of the entire year. That statement may surprise you and there are other sunrise and sunset facts that are equally as baffling.

We are taught from an early age that the greatest amount of daylight occurs on the first day of summer and the least amount on the first day of winter. This is the case in the northern hemisphere. However, this only means the gap between sunrise and sunset is at the greatest on the summer solstice and the least on the winter one.

When I explain this concept I like to use the image of two lines with a gap in the middle. If two lines are moving towards each other, the gap shrinks, this is when our days grow shorter. If the two lines are moving in opposite directions this is when our days grow longer. The harder case is when one line is moving opposite of the other. In that scenario depending on the rate things are changing and in which direction, the days can grow shorter or longer. This is where we are between Dec. 15 and 23. During that 9-day period, the sunsets will get later, but at a slower pace than the sunrises, which are also getting later. This means the gap shrinks or the daylight is still growing shorter.

Once we get beyond the Dec. 23 the speed at which the sunsets are growing later outpaces the sunrises. The amount of daylight grows because of the uneven change in sunrise and sunset. You’ll have to wait until Jan. 5 for the sunrises to get earlier. At this point the speed at which the daylight increases becomes noticeable. By the end of January we will have gained nearly an hour of daylight from where we stand on the winter solstice.

So the next logical question is why is this case? The basic answer is that the elliptical orbit of Earth around the sun, the shape of Earth and your place on it all are factors. While your definition of a day is 24 hours, scientifically a day is defined differently. For scientists a day is the time between two solar noons and a solar noon is the time of the day when the sun is at the highest point in the sky.

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A solar day is not exactly 24 hours long and varies quite a bit throughout the year. Actually, the solar day is longer than 24 hours around the summer and winter solstices and is shorter than 24 hours around the spring and autumnal ones. This means that the length of the solar day does not always match up to the length of a day as measured by a clock.

The image below illustrates why this is the case and can take some time to grasp. Suffice to say you will impress your coworkers if you tell them the sunsets are going to get later next week, even if the shortest day of the year is still two weeks away.