Tuesday January 4 is Perihelion Day. That’s the day of the year when the sun is closest to the Earth. On January 4th, the center of earth is 91,406,842 million miles from the center of the sun at 1:52 am. The opposite of Perihelion Day is Aphelion Day. That’s when the sun is farthest away from the earth. This year that occurs on July 4 at 3:10 am. Then the sun will be 94,509,598 miles away from the Earth. Viewed from Earth, that means the sun looks ever-so slightly bigger in January (about 7% bigger) and ever-so-slightly smaller in July.
Also, when the sun is closer to the Earth in the Northern Hemisphere, the Earth “speeds up” just a bit. That means the seasons are not quite the same length. If you think about it…February has only 28 days (29 in a leap year). July and August both have 31 days. In the Northern Hemisphere, spring and summer are a few days longer than fall and winter. In 2022, winter (Winter Solstice to Spring Equinox) is 89 days, 23 hours and 34 minutes. Spring is 92 days, 17 hours and 40 minutes long. Summer is 93 days, 15 hours and 49 minutes long. In the Southern Hemisphere, spring and summer are shorter than fall and winter.
Every 58 years, the date of Perihelion moves forward one day. This is part of a set of cyclical patterns known as the Milankovitch cycles. By the year 6430, perihelion will happen simultaneously with the March Equinox.
As is, here in Michigan, we calculate that because Perihelion Day occurs in January – in the middle of winter – that we are roughly 3 degrees F warmer in January and 3 degrees cooler in July, when the sun is farther away. This (slightly) minimizes the difference between winter and summer. By my calculation, in the year 12,368, perihelion will be on July 4. When that happens…it’ll be on average 3 degrees hotter in July and 3 degrees colder in January in Michigan. I’m not looking forward to that.
We are also now at our latest sunrise at 8:13 am. Sunsets are already starting to get later in the evening albeit at a rather slow pace in January. We’ve gained only 6 minutes and 16 seconds of daylight since the Winter Solstice back on Dec. 21.