JACKSON, Wyo. — Happy winter solstice! Saturday, Dec. 21, marks the first day of winter and the shortest day of the year in the Northern Hemisphere.
Buckrail spoke with Samuel Singer, executive director of Wyoming Stargazers, to unpack all things solstice, including general misconceptions about the astronomical event.
“The winter solstice is the 24-hour period where we have the largest percentage of dark hours after the sun sets and before the sun rises, and the shortest amount of daylight hours between the time of sunrise and sunset,” Singer said. “For astronomers, its awesome. We get more hours to observe the night time sky than any other night of the year.”
Singer said that the winter solstice is not the day that the sun sets earliest or rises latest. The earliest sunset is before Dec. 20 and the latest sunset is after Dec. 20, and the period between these two times is the winter solstice.
Singer explained to Buckrail the astronomy behind the winter solstice. He said that the earth’s northern hemisphere is pointing away from the sun at 23.5 degrees as it’s rotating around the sun, which causes the season of winter. Then in the summer, the earth is angled 23.5 degrees toward the sun, which causes warmer and longer days.
The earth’s tilt is reversed for the opposite hemisphere and that’s why it’s summer in the Southern Hemisphere at this time, according to Singer. Singer says the reason for the changing temperatures of the earth seasonally is a widely misunderstood concept.
“Some people think that the warming and cooling of the earth has to do with the distance that the earth is away from the sun,” Singer said. “It has absolutely nothing to do with that. The earth is actually closer to the sun during the Northern Hemisphere’s winter time than the Northern Hemisphere’s summer time.”
According to Singer, it’s the earth’s tilt and its relationship with the arc of the sun’s solar radiation that changes the temperature of the earth. When the earth is pointed away from sun in the winter, the atmosphere doesn’t heat up as much because the sun’s angle of radiation is spread out over a longer distance.
To help with the confusion, Singer shared an educational, rhyming phrase he learned to better understand the tricky topic of solstices: “Length of days and angles of rays, but nothing to do with how far away.”
Singer says to keep in mind that the axis of the earth is not changing from season to season.
“That 25.5 degree tilt is fixed,” Singer said. “The axis of the earth is always pointing up to the same location in space. Fortunately for us in the Northern Hemisphere, the rotational axis of the earth or pole points directly at the North Star. That’s why we call the North Star the ‘North Star’ or Polaris.”
Singer said that another misconception is that the winter solstice marks the first day of winter; it is actually during the apex or middle of winter.
“Our calendar uses these mid-point days, like the winter solstice, to define the beginning and ending of the seasons,” Singer said. “We should actually be using the cross-quarter days, the days that actually fall between the equinoxes and the solstices as the beginning and ending of the seasons.”
According to Singer, Halloween actually marks the beginning of winter and Christmas or the solstice marks the apex of winter; when it’s the shortest daytime and longest nighttime of the year. Then, starting next week, the days will gradually become longer and longer until reaching the end of the winter season around Groundhog Day on Feb. 2, which is another cross-quarter day.
“Ancient peoples in Europe and Mesoamerica used the cross-quarter days to actually keep track of the changes of the seasons,” Singer said.
Singer explained that colder temperatures occurring later in the winter also causes the misconception that the winter solstice marks the beginning of winter. He said that a “seasonal lag” decreases temperatures during the second half of winter or after the solstice.
“It takes a couple of months for the earth to warm up and to cool off, as we approach and get into each season, which is why the coldest time of winter is not around the solstice,” Singer said. “It is usually a little bit later in the winter, like January or February, when we get down into the negatives. So, the atmosphere and the earth are still cooling off from the fall.”
Conversely, in the summer time, the earth’s atmosphere starts to warm up in the spring, but high, apex temperatures aren’t reached until July or August.
