Astronomy Essentials

Latest sunsets follow summer solstice

Beautiful orange-to-blue sky after one of the year's latest sunsets, with high clouds and sun pillar.
Peter Gipson in Stowmarket, Suffolk, England, captured this June sunset – one of the year’s latest sunsets – in 2018. The vertical streak is what’s called a sun pillar. Thanks, Peter! Submit your image to EarthSky here.

Latest sunsets after summer solstice

For the Northern Hemisphere: Your latest sunsets – and latest evening twilights – are happening around now. They always come in late June and early July. Meanwhile, the Northern Hemisphere’s longest day fell on the June 20-21 solstice.

For 40 degrees north (Philadelphia, Pennsylvania; just north of Denver, Colorado; Beijing, China; Turkey; Japan and Spain), the latest sunsets are centered around June 27. The year’s latest sunsets always come after the summer solstice. But the exact date of the latest sunset depends on your latitude. Farther north – at Seattle – the latest sunsets happen on dates centered on June 25.

Even farther south – at Mexico City or Hawaii – the latest sunsets are centered on dates in early July.

For the Southern Hemisphere: Your latest sunrises of the year happen in late June and early July.

For the Northern or Southern Hemispheres: Latest sunsets go hand-in-hand with your latest twilights. The latest twilights of the year for 40 degrees north also happen in late June and early July. More about twilight below.

To find out the sunrise and sunset times for a given day, visit Sunrise Sunset Calendars.

Perspective view of dark clouds over bright sunset, long pier running toward horizon.
June sunset – Pere Marquette Beach in Muskegon, Michigan – via Jerry James Photography. Thank you, Jerry!

Why latest sunsets follow summer solstice

The latest sunsets comes after the summer solstice because the day is more than 24 hours long at this time of the year.

For several weeks, around the June solstice, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later by the clock in late June than it does on the June solstice. Therefore, the sunrise and sunset times also come later by the clock, as the table below helps to explain.

For Denver, Colorado

Date Sunrise Midday (Solar Noon) Sunset Daylight Hours
June 20 5:32 a.m. 1:01 p.m. 8:31 p.m. 14h 59m 15s
June 27 5:34 a.m. 1:03 p.m. 8:32 p.m. 14h 57m 57s

Source: timeanddate.com

Dark trees each side, colors yellow to orange to lavender to blue in sky.
Juan Argudin in Pembroke Pines, Florida, wrote on June 21, 2018: “We’ve taken dozens of sunset pictures but cannot remember such beautiful sunset colors. This was the first sunset after summer solstice, taken between 2 live oak trees in front of our house. Thank you for your excellent newsletter. We have learned a lot.” Photo by Olga Argudin. Thank you, Juan and Olga!

Clock time and sun time

If the Earth’s axis stood upright as our world circled the sun, and if, in addition, the Earth stayed the same distance from the sun all year long, then clock time and sun time would always agree.

However, the Earth’s axis is tilted 23.44 degrees out of vertical, and our distance from the sun varies by about 3 million miles (5 million km) throughout the year. At and around the equinoxes, solar days are shorter than 24 hours, yet at the solstices, solar days are longer than 24 hours.

That’s why the latest sunsets always come on or near June 27 at mid-northern latitudes every year.

At mid-northern latitudes, the later clock time for solar noon one week after the summer solstice is more substantial than the change in daylight hours. Given that the daylight hours on June 27 are almost the same as they were on the June 20-21 solstice, the later clock time for the June 27 solar noon gives us slightly later sunrise and sunset times, as well.

A word about twilight

There are three kinds of twilight:

Civil twilight starts at sundown and ends when the sun is 6 degrees below the horizon.

Nautical twilight occurs when the sun is 6 to 12 degrees below the horizon.

Astronomical twilight happens when the sun is 12 to 18 degrees below the horizon.

North of 50 degrees north latitude, there’s no true night in the month of June. In June, that far north, the sun never gets far enough below the horizon for true night to occur. So from 50 degrees north latitude – to the Arctic Circle (66.5 degrees north latitude) – you’ll find midnight twilight at this time of year.

And, above the Arctic Circle to the North Pole (90 degrees north latitude), this time of year is the time of the midnight sun.

Read more: What exactly is twilight?

A diagram showing the sun's distance below the horizon at civil twilight, nautical twilight and astronomical twilight.
Skywatchers learn to recognize the subtle gradations of twilight. True night doesn’t begin until the sun sinks 18 degrees beneath the horizon. North of 50 degrees north latitude, there is no true night in June because the sun never gets far enough below the horizon. Visit Sunrise Sunset Calendars for the times of civil, nautical and astronomical twilight in your sky. Image via Wikipedia.

Bottom line: Why don’t the latest sunsets come on the longest day (the solstice)? In a nutshell, it’s a discrepancy between the sun and the clock. Thus, for mid-northern latitudes, the latest sunsets always come in late June.

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Posted 
June 24, 2021
 in 
Astronomy Essentials

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