Longest sunsets happen around the solstice

Longest sunsets: Large, bright yellow circle of sun in deep orange sky with jet plane crossing in front of it.
View at EarthSky Community Photos. | Steve Pond in Sussex, U.K., caught this sunset and plane from a family camp in the Sussex countryside on June 17, 2022. The sun takes longer to set – causing the longest sunsets – around the time of a solstice. Thanks, Steve!

In 2023, the Northern Hemisphere’s summer solstice – and Southern Hemisphere’s winter solstice – falls on June 21, 2023, at 14:58 UTC (that is 9:58 a.m. in central North America; translate UTC to your time). Read more about the June solstice, here.

Longest sunsets in June and December

Here’s a natural phenomenon you might not have imagined. That is, the longest sunsets happen around the time of the solstices. We’re talking about how many seconds it takes for the body of the sun to sink below your western horizon. Sunsets take a longer time around solstices, and a shorter time around equinoxes. It’s true whether you live in Earth’s Northern or Southern Hemisphere.

As viewed from both the Northern and Southern Hemispheres, the sun rises and sets farthest north at the June solstice and farthest south at the December solstice.

Now consider that the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. That means a longer duration for sunset at the solstices.

Meanwhile, at an equinox, the sun rises due east and sets due west. That means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.

Longest sunsets are how long?

The sunset duration varies by latitude. But let’s just consider one latitude – 40 degrees north – the latitude of Denver or Philadelphia in the United States, Sardinia in the Mediterranean, or Beijing in China.

At that latitude, on the day of a solstice, the sun sets in about 3 1/4 minutes.

That’s half a minute longer than the sunset at the same latitude on the day of an equinox. The equinox sun at 40 degrees north latitude sets in roughly 2 3/4 minutes.

At more northerly temperate latitudes, the sunset duration is greater; and at latitudes closer to the equator, the sunset duration is less. Near the Arctic Circle (65 degrees north latitude), the duration of a solstice sunset lasts about 15 minutes. At the equator (0 degrees latitude), the solstice sun takes a little over 2 1/4 minutes to set.

Regardless of latitude, however, the duration of sunset is always longest at or near the solstices.

The sunsets are longer in December than June

As it turns out, the sunset and sunrise are a tad longer on the December solstice than they are on the June solstice.

That’s because the sun is closer to Earth in December than it is in June. Therefore, the sun’s disk looms a bit larger in our sky in December, and so it takes slightly longer to set.

Additionally, the closer December sun moves eastward upon the ecliptic at a faster clip, helping to slow down the December solstice sunset (and sunrise) even more. For instance, at 50 degrees north latitude, the winter solstice sunset (sunrise) lasts about 4 minutes and 18 seconds, or about 8 seconds longer than the sunset (sunrise) on the summer solstice.

And now you know!

Four photos of half-lit Earth, left two at a slant and right two straight up and down.
Equinoxes and solstices, via Geosync. The Earth’s axis points straight up and down, with north at the top. The solstices are on the left (December solstice at top, June solstice at bottom) and the equinoxes are to the right (March equinox at top, September equinox at bottom). Image via NASA.

Some sunsets from EarthSky Community Photos

Large yellow sun in orange sunset clouds, over the ocean, with a ship in the distance.
View at EarthSky Community Photos. | Meiying Lee of Taoyuan, Taiwan, captured this image on May 27, 2023, and wrote: “Yesterday (May 27th), just before the arrival of the typhoon, the sky in Taiwan was exceptionally clear. I specifically went to the seaside and captured the phenomenon of a sun mirage during the sunset, amidst the beautiful red hues scattered across the sky. Two groups of sunspots were also recorded, but others were blocked by clouds. At that moment, a ship happened to pass in front of the sun, making the steam emitted by the ship’s chimney particularly visible due to its proximity to the sun.” Thank you, Meiying!
Reddish sunset picture with yellow sun behind veil-like red clouds.
View at EarthSky Community Photos. | Brandi Mullins of Fieldale, Virginia, captured this image on June 6, 2023, and wrote: “The sunset this afternoon was absolutely beautiful! I was very fortunate to capture this moment before it vanished behind the clouds and was gone as quickly as it came.” Thank you, Brandi.

Bottom line: Here’s a natural phenomenon you might never have imagined. That is, the longest sunsets happen around the time of a solstice.

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June 20, 2023

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Bruce McClure

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