When is Sunset : Types of Sunset

When is sunset : While the length of a day on Earth appears to be constant at 24 hours, the amount of sunshine we receive varies drastically throughout the year.

The longest-duration days are experienced at the summer solstice, with the most polar latitudes experiencing the most daylight.

Ask Ethan: When Is The Year’s Earliest And Latest Sunrise And Sunset?

If you live near the equator, though, the number of hours the Sun spends in the sky doesn’t change much during the year, from summer solstice to equinox to winter solstice and again.

But, as Patreon supporter Ben Turner points out, solstices don’t dictate everything about the length of a day.

We all know that the solstices are the year’s longest and shortest days, but given the analemma, what are the earliest and latest sunrise/sunset times? Is it the same across all latitudes?

It’s not a consistent storey, and it’s a complicated one. Let’s have a look at why that is.

This is the analemma: the form obtained by photographing the Sun every day of the year from the same position at the same time.

This specific analemma was captured in the afternoon in the northern hemisphere of Earth.

The form and orientation of the analemma indicate this. The smaller loop of this figure-8 is always higher up in the northern hemisphere, whereas the larger loop is always higher up in the southern.

The analemma would be fully vertical if photographed at high noon, when the Sun reaches its highest angular height above the horizon, but it tips as if spun counterclockwise earlier in the day and clockwise later in the day.

The summer solstice is always at the tip of the analemma’s long axis, whereas the winter solstice is at the opposite tip.

The analemma’s distinctive shape is due to the interaction of two factors:

As it rotates, the Earth is tilted on its axis at 23.5° relative to the Earth’s orbital plane.

Moreover, the Earth orbits the Sun in an ellipse rather than a complete circle.

Our analemma would be a single point if the Earth’s axis was not slanted as it revolved, and our planet also orbited in a perfect circle around the Sun.

With each passing day, our planet would revolve a full 360° in 23 hours and 56 minutes, then take an extra 4 minutes to “catch up” to the Sun’s former position in the sky, because we’re both revolving about it.

Our days are 24 hours long because we have to rotate more than 360 degrees to finish a whole day.

We can start adding in the other impacts once we understand how the Solar System works.

Because our globe is tilted on its axis, the Sun’s journey through the sky varies throughout the year.

When comparing the June and December solstices, the apparent location of the Sun will shift by 47°, which is twice our axial tilt.

If you looked at the top-to-bottom angular scale of our analemma over its long axis, you’d see that it was 47° in the sky from every point on the planet.

Our analemma would be a completely symmetric figure-8 if our planet was only inclined but still orbited in a perfect circle. The “8” would have two symmetric lobes that would intersect in the middle at the equinoxes.

After the equinoxes in the spring and fall, the Sun rises and sets later than usual, while after the solstices in the summer and winter, the Sun rises and sets earlier than usual.

However, the eccentricity has a secondary effect.

When the Earth is closer to aphelion (far away from the Sun), it orbits the Sun more slowly than usual, causing our planet to advance faster than it needs to in a 24-hour period.

The Earth circles faster than the average when it is closest to the Sun (near perihelion), therefore our planet rotates somewhat less than it has to in order to return the Sun to the same exact place after 24 hours.

Because of this effect, and because perihelion occurs shortly after the December solstice (while aphelion occurs shortly after the June solstice), the “December solstice” side of the analemma is much wider, with larger time differences, whereas the “June solstice” side is much narrower, with smaller deviations from the mean time.

During the end of the year, there is constructive interference between these two effects, but during the middle of the year, there is destructive interference.

All latitudes on Earth have the same equation of time, which is the combined effect of our revolution around the Sun and its orbital eccentricity with the influence of our rotation and axial tilt.

Everything is earlier as we get closer to the June solstice.

Even though the days are longer in the northern hemisphere, dawn and sunset are both shifted to slightly earlier timings at earlier dates.

Someone living near the Arctic Circle will see their first dawn 1-3 days before the solstice, whereas someone living in the mid-latitudes (about Washington, D.C.) will see it a week before the solstice, and someone near the Tropic of Cancer will see it two weeks before the solstice.

Similar shifts occur in the southern hemisphere in a latitude-dependent manner, with the exception that you get your earliest sunsets since the days are shorter.

Similarly, the later sunsets for northern hemisphere observers witness the same latitude-dependent shifts, except after the June solstice, due to the way the equation of time changes (where it turns sign very close to each solstice).

The latest sunsets come 1-3 days after the solstice in the Arctic Circle; mid-latitudes see their latest sunsets approximately a week after the solstice; and Tropic of Cancer-like latitudes get their latest sunsets around July 4th.

Similar shifts occur in the southern hemisphere, and they are also latitude-dependent.

The significant distinction is that those are the times when you’ll see the most recent sunrises of the year.

What’s fascinating about all of this is that the experiences of the northern and southern hemispheres during the June solstice aren’t exactly reversed at the December solstice.

The time shifts at the December solstice are larger than the June solstice because the equation of time has significantly more pronounced changes when the influences of obliquity and ellipticity constructively conflict.

This is something you would have guessed based on the analemma’s shape.

You should expect sunset/sunrise times to be displaced by a higher amount on the side where the lobe of the figure-8 is larger and displasys greater time discrepancies than on the side where the lobe of the figure-8 is smaller.

Much more dramatic changes occur in the large lobe, which corresponds to the December solstice.

As a result, you’ll need to not only switch the hemispheres and sunrise/sunset effects from June to December, but the combined impacts of obliquity and ellipticity will boost the effects of early/late sunrise/sunset times by by 50%.

When the Earth approaches the Sun, its velocity is substantially quicker than at other times, causing large shifts in how far our clocks deviate from an astronomical “mean time” between sunrise and sunset.

On April 14th and August 30th, the equation of time reverts to a symmetrical state.

These dates, which are around 3 weeks after the March equinox and 3 weeks before the September equinox, are unimportant.

They are determined by the alignment of our planet’s orbit around the Sun with our seasons, which are determined by axial tilt.

Our analemma’s shape, as well as Earth’s time equation, are not fixed.

Our planet’s perihelion and aphelion will be aligned with our equinoxes in about 5,000 years, transforming our analemma from a figure-8 shape to a teardrop shape.

Our earliest sunrise and latest sunset will occur on the summer solstice, while our latest sunrise and earliest sunset will occur on the winter solstice, when this alignment reaches perfection in the not-too-distant future.

Although the exact times of those occurrences will differ depending on latitude, they will all take place on the same dates for all observers on Earth.

Our sunset and dawn times will shift from year to year as long as our planet’s axis precesses, which should last longer than our Sun shines.

We can finally comprehend how because of our axial tilt and eccentric orbit.