What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.

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The longest days are in December

What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.

But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.

Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.

Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.

Why are the days longer in December?

The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.

The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.

There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.

For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.

Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.

Sunrises and sunsets

Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.

In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.

The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.

However, at the same time … It’s the season of bountifully long solar days.

Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.

Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.

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The post Longest days accompany the December solstice first appeared on EarthSky.

November 3, 2023, ushers in the earliest solar noon – for the whole year and for the entire globe – by the clock. Solar noon is a natural rather than artificial construct, although our clocks and calendars measure its continual shift throughout the year. Solar noon – aka midday – refers to that passing instant when the sun reaches its highest point for the day, midway between sunrise and sunset. If you reside along the center line of your time zone, then solar noon – or midday – comes at 11:44 a.m. by your clock every year in early November. If you’re not on your time zone’s center line – and most of us aren’t – solar noon happens a bit earlier or later by your clock, depending on your offset from your time zone’s center line.

Obscure? Possibly. But the shift in solar noon is tied to a phenomenon that many people around the world might notice in the coming weeks. That is, the earliest solar noon of the year is a prelude to the year’s earliest sunset in the Northern Hemisphere – and the year’s earliest sunrise in the Southern Hemisphere.

You thought the earliest sunset for the Northern Hemisphere came at the December solstice? It doesn’t. It happens well before that solstice, for a reason that’s related to the earliest solar noon on November 3.

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Earliest and latest solar noons, and the length of the day. The first several days of November, from everywhere worldwide, the days (as measured from one solar noon to the next) are almost exactly 24 hours in duration. Thereafter, day by day, solar noon comes later and later by the clock, lessening the discrepancy between sun time and clock time. At long last – on December 25, 2023 – the sun and the clock agree with one another, with solar noon coming at 12 noon by the clock (for those at the center line of a given time zone).

Although the sun and clock will agree on December 25, 2023, the duration of the solar day – as measured from one solar noon to the next – will continue to exceed 24 hours each day for another six weeks.

Finally, the latest solar noon will arrive on or near February 11, at 12:14 p.m. by the clock (at the time zone center line).

And, for everyone, everywhere worldwide, solar noon comes some 30 minutes earlier by the clock on November 3, 2023, than it will on February 11, 2024.

Want to know the clock time for solar noon (midday) at your location? Visit Sunrise Sunset Calendars, remembering to check the solar noon box.

Want to know the time difference between sun and clock for any date? Go to AstroPixels.com and look under the equation of time column.

Solar noon and earliest sunset (and/or sunrise). So … November 3, 2023, marks the earliest solar noon of the year for the whole globe. What’s more, residents at the Earth’s equator have their earliest sunrise and sunset on November 3. That’s because, at the equator, the daylight hours remain virtually the same throughout the year – so the earliest sunrise, earliest solar noon and earliest sunset all fall on the same day.

Elsewhere – within the tropical and temperate regions of the world – the shortest period of daylight happens on the day of the winter solstice, and the longest period of daylight on the summer solstice. So if you live near the Arctic Circle, your earliest sunset doesn’t happen until around the December (winter) solstice; or if you live near the Antarctic Circle, your earliest sunrise doesn’t take place until around the December (summer) solstice.

That’s in spite of the earliest solar noon coming in early November all over the world.

Read more: December solstice starts shortest season

If you live north of the equator but south of the Arctic Circle, your earliest sunset occurs somewhere between November 3, 2023, and December 21, 2023. In the Northern Hemisphere, those living closer to the equator have an earlier date for their earliest sunset; and those lodging closer to the Arctic Circle have a later date for their earliest sunset.

We give the approximate dates for the earliest sunset in the Northern Hemisphere:

15 degrees north latitude
Earliest sunset on or near November 23

30 degrees north latitude
Earliest sunset on or near December 1

45 degrees north latitude
Earliest sunset on or near December 10

60 degrees north latitude
Earliest sunset on or near December 17

In the Southern Hemisphere, it’s your earliest sunrise that takes place between November 3, 2023, and December 21, 2023. The closer you live to the equator, the earlier the date for the earliest sunrise; and the closer you live to the Antarctic Circle, the later the date for the earliest sunrise. Because comparable latitudes north/south of the equator have the same approximate dates for earliest sunset/earliest sunrise, the dates for the Southern Hemisphere’s earliest sunrises can be gleaned from the listing above.

In the Northern Hemisphere, the latest sunrise must wait till after the Northern Hemisphere’s December winter solstice; and in the Southern Hemisphere, it’s the latest sunset that must wait till after the Southern Hemisphere’s December summer solstice. Those living closer to the Arctic or Antarctic Circles have an earlier date for their latest sunrise/latest sunset; and those lodging closer to the Earth’s equator have a later date for their latest sunrise/latest sunset. Here are the approximate dates for the Northern Hemisphere’s latest sunrise/Southern Hemisphere’s latest sunset at various latitudes:

60 degrees latitude: December 27
45 degrees latitude: January 2
30 degrees latitude: January 11
15 degrees latitude: January 23

Two reasons account for the unequal length of the solar day over the year. First and foremost, the tilt of the Earth’s axis causes the solar day to be more than 24 hours long around the solstices yet less than 24 hours long around the equinoxes. However, Earth’s eccentric orbit plays a secondary role, either accentuating or lessening the effect. At the December solstice, the Earth is some 3 million miles (5 million km) closer to the sun, and moving more swiftly in its orbit, than on the June solstice. Therefore, the longer-than-average solar day at the December solstice (24 hours + 30 seconds) outlasts the longer-than-average solar day at the June solstice (24 hours + 13 seconds).

Bottom line: November 3 brings the year’s earliest solar noon – that is, earliest midday – by nature’s clock. It’s a harbinger of the Northern Hemisphere’s earliest sunset.

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The post Year’s earliest solar noon on November 3 first appeared on EarthSky.

We celebrate the September equinox as the first day of autumn for the Northern Hemisphere, and first day of spring for the Southern Hemisphere.

What is it? It’s a milestone in Earth’s orbit around the sun. At an equinox, the sun appears directly above Earth’s equator. At the September equinox, it’s crossing from north to south.
When is it? The September equinox will fall at 12:44 UTC (7:44 a.m. CDT) on September 22, 2024.
Note: The name equinox comes from the Latin aequus (equal) and nox (night). At the equinox, days and nights are said to be equal in length for everyone across the globe. And it’s true. They are approximately equal.

Read more: Why aren’t day and night exactly equal on the equinox?

Earth’s tilt causes it

The earliest humans spent more time outside than we do. They used the sky as both a clock and a calendar. And they could easily see that the sun’s path across the sky, the length of daylight and the location of the sunrise and sunset all shift in a regular way throughout the year.

The equinoxes and solstices happen because Earth tilts on its axis by 23 1/2 degrees. Because of the Earth’s tilt, the Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly. The solstices indicate our greatest (or least) tilt toward the sun, in either hemisphere. The equinoxes fall midway between the solstices.

And, indeed, Earth’s two hemispheres receive the sun’s rays about equally around equinox time.

But Earth never stops moving in orbit around the sun. And these days of approximately equal daylight and night will change quickly, as we move toward the December solstice.

Maybe you’ve noticed that the length of daylight changes more quickly from day to day around the equinoxes than around the time of the solstices?

A good day to find due east and due west

The day of an equinox is a good day for finding the directions due east and due west from your favorite place to watch the sky. The sun rises due east and sets due west at the equinoxes. It’s true no matter where you live on Earth. Why? Because we all see the same sky.

Everywhere on Earth, except at the North and South Poles, you have a due east and due west point on your horizon. And each point marks the intersection of your horizon with the celestial equator, the imaginary line above the true equator of the Earth.

At the equinoxes, the sun appears overhead at local solar noon as seen from Earth’s equator, as the illustration below shows. The sun is on the celestial equator. The celestial equator intersects due east and due west for everyone around the globe. So the sun rises and sets due east and due west at the equinox.

So go outside around sunset or sunrise on the day of an equinox. And notice the location of the sun on the horizon with respect to familiar landmarks. If you do this, you’ll be able to use those landmarks to find those cardinal directions in the weeks and months ahead, long after Earth has moved on in its ceaseless orbit around the sun.

Signs of the September equinox in nature

The signs that summer is gone – and winter is coming – are everywhere now, on the northern half of Earth’s globe. In the Northern Hemisphere, dawn comes later, and sunset earlier. Also, notice the arc of the sun across the sky. It’s shifting southward now. And birds and butterflies are migrating south, along with the path of the sun.

The shorter days are bringing cooler weather. A chill is in the air. In New York City and other fashionable places, some people have stopped wearing white. Creatures of the wild are putting on their winter coats.

All around us, trees and plants are ending this year’s cycle of growth. Perhaps they’re responding with glorious autumn leaves, or a last burst of bloom before winter comes.

In the night sky, Fomalhaut – our Autumn Star – is making its way across the heavens each night.

September equinox images from EarthSky’s community

Bottom line: The September equinox is here! It’ll arrive at 12:44 UTC on September 22, 2024. The sun will be exactly above Earth’s equator, moving from north to south. Autumn for the Northern Hemisphere. Spring for the Southern Hemisphere. Here’s all you need to know.

Read: Year’s fastest sunsets at equinox

Read more: Equinox shadows trace a straight line from west to east

The post 2024 September equinox: All you need to know first appeared on EarthSky.

A moon analemma

Maybe you’ve already heard of a sun analemma, which is a composite photo of the sun taken over the course of many months. If they’re done correctly, such composites trace out a figure-8 path. Likewise, photos of the moon can be used to create a figure-8 path in our sky, over the course of a lunar month. NASA explains how to capture a moon analemma:

On average, the moon returns to the same position in the sky about 50 minutes and 29 seconds later each day. So, photograph the moon 50 minutes 29 seconds later on successive days. Over one lunation or lunar month it will trace out an analemma-like curve as the moon’s actual position wanders due to its tilted and elliptical orbit.

Wael Omar’s lunar analemma

Wael Omar explained his journey to this image:

The journey of this image was really challenging and exhausting. On top of that were the sleepless nights I went through to stay awake waiting for the scheduled time to take the image of the moon. There were also some cloudy nights, and I was a little lucky to see the moon through it when the time of the shoot came.

I used a Canon 200D camera with 18mm lens. During the last week, the images were during daytime. That’s why the moon images on these days are a little blue. They were so faint, but I could see them when I zoomed deeply on the images. Of course, the details were absent, so I came up with an idea to use my GOTO mount to point to the location of the moon. (It would be impossible to see it with the unaided eye.) Then I took images with the help of my Redcat 51 scope. Finally, I put them in the same location of the moon on the 18mm lens image.

I took a vacation from work on the last two weeks to be ready for the moon images, as they were after midnight and during daytime. I exerted so much effort to image the foreground, as I climbed up a 50-meter-high building to have a clear view of the pyramids. Then I blended this view with the total analemma I imaged.

Your efforts were well worth it, Wael!

Bottom line: A moon analemma follows the path of the moon over the course of a lunar month. Thanks to Wael Omar for this stunning composite image!

The post Moon analemma over Egypt’s Great Pyramids first appeared on EarthSky.

Latest solar noon comes in February

For you, if you’re time-conscious … February 11 marks the latest solar noon for all of 2023, and for the entire globe, by the clock. However, solar noon isn’t a clock event, even though our clocks and calendars measure its continual shift throughout the year. So what is it? It’s a natural event. Solar noon – aka midday – refers to that passing instant when the sun reaches its highest point for the day, midway between sunrise and sunset.

At solar noon, the sun is said to cross your meridian, as depicted on the diagram below. No matter where you live worldwide, the sun can only be at one of three places in your sky at solar noon: at your zenith (straight overhead), south of zenith, or north of zenith. The noonday sun can only reach zenith at the tropics. From northern temperate latitudes, the noonday sun is always south of zenith. At southern temperate latitudes, the noonday sun is always north of zenith.

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The equation of time

We invite you to check out the graph below. It shows what’s called the equation of time. That’s a fancy name for the discrepancy between solar noon and clock noon. As the graph shows, the latest solar noon in February occurs a solid 1/2 hour later by the clock than the year’s earliest solar noon in early November.

Yearly, the latest solar noon happens on (or near) February 11 and the earliest solar noon happens on (or near) November 3. That’s true no matter where you live worldwide. North, south, east, west on the globe … doesn’t matter. For all of us, solar noon happens over 30 minutes later by the clock on February 11 than it does on November 3.

Before the advent of time zones and standard time, the equation of time graph (below) applied to anywhere worldwide. In our day and age, the graph refers to places that reside on the center line of a given time zone. For example, Denver, Colorado – at 105 degrees west longitude – sits on the center line of the Mountain Standard Time zone. So, in Denver, solar noon reads 12:14 p.m. by the clock on February 11, and 11:44 a.m. by the clock on November 3.

Elsewhere within a given time zone, the standard clock time for solar noon differs. Keep reading to understand why.

Where are you in your time zone?

Earth is divided into around 24 time zones, and each time zone is (in theory) 15 degrees of longitude wide. Because Earth is a sphere, time zones are widest across at the equator. They reduce in width as you go north or south, until they reach to zero degrees at the poles. In other words, the time zones meet at the poles. So, at the equator, a time zone is (in theory) about 1,035 miles (1,665 km) wide. By the way, we keep saying “in theory” because time zone borders typically aren’t straight lines. They’re often drawn in a zigzag fashion to accommodate the boundaries of nations, states or provinces.

But for all of us – unless you live at Earth’s North or South Pole – your time zone has some width to it. And you might have noticed that sunrise and sunset in the sky happen later (by the clock) as you go directly west in a given time zone.

So it is for solar noon. Solar noon comes 4 minutes later by the clock for every 1 degree you live west of your time zone’s eastern edge. Solar noon comes 4 minutes earlier by the clock for every 1 degree you live east of your time zone’s western edge. No matter. It’s still the case that – in any year, and at any location – solar noon happens 1/2 hour later by the clock on February 11 than on November 3.

By the way, we emphasize we’re talking about standard time. We are not talking about daylight saving time or summer time, in which we pretend that it’s one hour later than it is.

But there’s no need to go through mental gymnastics to figure out the clock time for solar noon in your location. Simply visit the Sunrise Sunset calendar site, enter your location, and look at the column marked solar noon.

In this way, you’ll know your clock time for solar noon for any day of the year.

Unequal length of solar days

The day – as measured from one solar noon to the next – rarely equals 24 hours. In fact, a 24-hour solar day happens but four times a year, on or near these dates: February 11, May 14, July 26 and November 3. Again, we invite you to study the equation of time graph above. The 24-hour solar days only take place at the turning points above (February 11 and July 26) and below (May 14 and November 3).

The sun and the clock only agree 4 times a year: on or near April 15, June 15, September 1 and December 25. Look at the graph above and you can see that the solar day is shorter than 24 hours on April 15 and September 1, yet longer than 24 hours on June 15 and December 25.

Shorter days at equinoxes, longer days at solstices

Earth-sun geometry dictates seasonal variation in the length of solar days. Solar days are less than 24 hours long for roughly 3 months centered around the equinoxes (March 20 and September 23). And solar days are longer than 24 hours for roughly 3 months centered around the solstices (June 21 and December 21).

Two reasons account for the unequal length of the solar day. First and foremost, the tilt of the Earth’s axis causes the solar day to be more than 24 hours long around the solstices, and less than 24 hours long around the equinoxes. But Earth’s eccentric orbit plays a role, too, either accentuating or lessening the length of the solar day.

Around the December solstice, the Earth is some 3 million miles (5 million km) closer to the sun than on the June solstice. So Earth travels most swiftly in its orbit for the year in December and January. It travels most slowly in June and July.

Hence, at and around the December solstice, the Earth must rotate farthest on its axis for the sun to return to its noontime position. That gives us the year’s longest solar days around the December solstice: 24 hours + 30 seconds.

In contrast, the solar days accompanying the June solstice are considerably shorter: 24 hours + 13 seconds.

Mean sun versus real sun

In short, the mean sun used by the clock is a fiction. The clock presumes Earth’s rotational axis stands upright as we revolve around the sun. The clock also presumes Earth goes around the sun in a perfect circle. Neither presumption is correct. Earth’s rotational axis is titled nearly 23.5 degrees out of perpendicular to its orbital plane. And, as mentioned before, Earth’s distance from the sun varies by about 3 million miles (5 million km).

The mean solar day is 24 hours long. But the real solar day (as measured by the sundial) varies in length throughout the year. The discrepancy between the clock and the sundial is never greater than 1/2 minute on any given day. Even so, the discrepancy accumulates daily for roughly three months. That’s why the latest solar noon in February comes 1/2 hour later by the clock than the earliest solar noon in early November.

Want to know the time difference between the clock and sundial for any day of the year? Go to this online calculator and scroll down to the equation of time column (first column). Additionally, you can find out the solar day duration under the fifth column.

Zero shadow day

For those living between the Tropic of Cancer and Tropic of Capricorn, twice a year, you’ll have a zero shadow day. That’s when – from your location – the declination of the sun is equal to your latitude. So when that happens, the sun crosses your local meridian at your zenith – the point directly overhead – and does not cast a shadow. Of course, the date this occurs, varies by location.

For example, the city of Bengaluru, India, celebrate zero shadow day every year on April 25 and August 18.

Bottom line: February 11 ushers in the latest noontime sun of the year, by nature’s clock. And for folks living at the Earth’s equator, this date also marks the day of the year’s latest sunrise and latest sunset.

The post Year’s latest solar noon happens on February 11 first appeared on EarthSky.

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Personal solstices: photos by the EarthSky community

Personal solstices in shadows

Bottom line: Personal solstices – photos from the EarthSky community around the world – showing what the December solstice means to them.

The post Personal solstices: EarthSky community photos first appeared on EarthSky.

Submit your photo to EarthSky Community Photos

See also: Solar analemma on June 20, 2021

See also: Matthew Chin’s solar analemma from 2014

The post Analemma of the moon, from Hong Kong first appeared on EarthSky.

Rick Williams of Woodland, California, caught this image on the day of the solstice, June 20, 2021. It’s what’s called an analemma, a figure-8 curve showing the position of the sun at a chosen time (often noon) over a year. Rick wrote of this image that he captured it …:

… a few seconds before noon PST (=1 PM PDT) on the solstice … A small stationary mirror reflects sunlight onto the wall. I marked the center of the reflected light each day over the course of 2 years at exactly noon PST. When connected, the dots form an analemma mapping out the sun’s annual course.

Rick wrote:

At the solstice (sol=sun, sistere= to stand still), the declination of the sun seems to “pause” and reverses its course. On any given day, a horizontal line through the sun’s position shows the latitude at which the sun is directly overhead at solar noon, in this case, 23.5 degrees North.

A vertical line through the position intersects the Equation of Time correction scale (just below the 10 degree North line). This shows the difference between solar time and standard time for that day; in this case, about + 8-10 minutes, corrected for longitude (today exactly 8 m 36 s). Solar/sun time is on the slow side, so 8.5 minutes can be added to obtain standard time; if the minute number is negative, solar time is faster, and that amount is subtracted to compute standard time. Standard time is the average of these times; solar time is the same as standard time on only four days of the year. This is the explanation for analemmas in the Pacific Ocean on many globes, which also have a time scale reflecting the Equation of Time at the Prime Meridian. This scale is corrected for my longitude, 121.77 degrees West.

Bottom line: An analemma is a figure-8 curve showing the position of the sun at a chosen time of day (often, noon) over a year. Here’s one on the side of a house.

The post Analemma shows the sun’s path over a year first appeared on EarthSky.

The winter solstice is the shortest day. It offers the shortest period of daylight. But, unless you live close to the Arctic Circle or Antarctic Circle, your earliest sunsets aren’t on or even near the solstice itself. Instead, your earliest sunsets will come before the winter solstice. The exact date of earliest sunset depends on your latitude. If you live in the southernmost U.S., or a comparable latitude (say, around 25 or 26 degrees north latitude), your earliest sunsets are in late November. If you’re farther north – say, around 40 degrees north latitude – your earliest sunsets are around December 7.

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And if you live in the Southern Hemisphere, your earliest sunrises are coming around now. Southern Hemisphere? Click here.

Why isn’t the earliest sunset on the year’s shortest day? To understand it, try thinking about it in terms of solar noon or midday, the time midway between sunrise and sunset, when the sun reaches its highest point for the day.

A clock ticks off exactly 24 hours from one noon to the next. But the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.

So the exact time of solar noon, as measured by Earth’s spin, shifts in a seasonal way. If you measured Earth’s spin from one solar noon to the next, you’d find that – around the time of the December solstice – the time period between consecutive solar noons is actually half a minute longer than 24 hours.

So – two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time (the time on your clock wherever you are around the globe). Two weeks later – on the winter solstice – the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.

The later clock time for solar noon also means a later clock time for sunrise and sunset.

Visit Sunrise Sunset Calendars for the December 2020 calendar, giving you the clock time for solar noon (check the solar noon box).

The result: earlier sunsets before the winter solstice and increasingly later sunrises for a few weeks after the winter solstice.

The exact date of earliest sunset varies with latitude. But the sequence is always the same. For the Northern Hemisphere, earliest sunset in early December, winter solstice, latest sunrise in early January.

Meanwhile, if you’re in the Southern Hemisphere, take nearly everything we say here and apply it to your winter solstice in June. For the Southern Hemisphere, the earliest sunsets come before the winter solstice, which is typically around June 21. The latest sunrises occur after the June winter solstice.

During the month of December, it’s nearly summer in the Southern Hemisphere; the summer solstice comes this month for that hemisphere. So sunsets and sunrises are shifting in a similar way. For both hemispheres, the sequence in summer is: earliest sunrises before the summer solstice, then the summer solstice itself, then latest sunsets after the summer solstice.

As always, things get tricky if you look closely. Assuming you’re at a mid-temperate latitude, the earliest sunset for the Northern Hemisphere – and earliest sunrise for the Southern Hemisphere – comes about two weeks before the December solstice, and the latest sunrise/latest sunset happen about two weeks after.

But at the other end of the year, in June and July, the time period is not equivalent. Again assuming a mid-temperate latitude, the earliest sunrise for the Northern Hemisphere – and earliest sunset for the Southern Hemisphere – comes only about one week before the June solstice, and the latest sunset/latest sunrise happens about one week after.

The time difference is due to the fact that the December solstice occurs when Earth is near its perihelion – or closest point to the sun – around which time we’re moving fastest in orbit. Meanwhile, the June solstice occurs when Earth is near aphelion – our farthest point from the sun – around which time we’re moving at our slowest in orbit.

In short, the earliest sunset/winter solstice/latest sunrise and earliest sunrise/summer solstice/latest sunset phenomena are due to the fact that true solar days are longer than 24 hours long for several weeks before and after the solstices. At and around the solstices, the Earth must rotate farther on its axis for the sun to return to its daily noontime position, primarily because the sun is appreciably north or south of the Earth’s equator.

However, perihelion accentuates the effect around the December solstice, giving a day length of 24 hours 30 seconds. And aphelion lessens the effect around the June solstice, giving a day length of 24 hours 13 seconds.

Bottom line: The earliest sunsets and latest sunrises don’t come on the winter solstice, the shortest day of the year. Instead, earliest sunsets come some weeks before the winter solstice. Latest sunrises come some weeks after it.

Here are more details about the earliest sunsets.

The post When is my earliest sunset? first appeared on EarthSky.

In the jargon of astronomers and celestial navigators, your local meridian is an imaginary semi-circle that crosses your sky’s dome from due north to due south. The point where the sun crosses that arc – when the sun is highest for that day – is variously called solar noon, or midday, or high noon, or local noon or just plain noon.

An astronomer might say that the sun is making an upper meridian transit at such a time.

When does it happen for you each day? It might or might not surprise you to learn it doesn’t usually happen at noon on your clock.

At solar noon, the sun can be at one of three places: at zenith (straight overhead), north of zenith or south of zenith. At temperate latitudes in the Northern Hemisphere, the noonday sun is never at zenith but is always found in the southern sky.

At temperate latitudes in the Southern Hemisphere, the noonday sun is never at zenith but is always found in the northern sky.

The noonday sun can only be at zenith in the tropics.

The shortest shadow of the day comes at solar noon, or when the sun transits your local meridian. North of the Tropic of Cancer, the noonday shadow always points due north.

South of the tropic of Capricorn, the noonday shadow always points due south.

Generally speaking, noon by the sun and noon by the clock seldom agree. Noon by the sun is a natural phenomenon, based on the sun’s highest point for the day. Noon as defined by the sun long preceded the invention of clocks and the introduction of time zones. Needless to say, noon by the sun also preceded so-called daylight saving time or summer time, whereby we pretend that it’s one hour later than it is.

Consider that – within a single time zone – noon by the sun comes earlier by the clock at the eastern edge of the time zone, yet later by the clock at the western edge of the time zone. You might notice if you routinely travel east or west within your time zone.

You don’t need a clock to find out when the sun reaches its noontime position. At solar noon, the shortest shadow of the day points due north at northern temperate latitudes (or due south at southern temperate latitudes).

With the eye alone, it’s difficult to know exactly when the shadow shrinks to its shortest length. But, given a full day of sunshine, we can use the method of equal altitudes to find due north (or due south) and our local meridian.

Here’s how you do it. Place a plumb or vertical stick into the ground. Note the length of any morning shadow. Then wait until the shadow reaches this same length in the afternoon. Bisect this angle to find due north (or due south). For a fuller explanation, click into MySundial online and scroll down to 4. The “Method of Equal Altitudes.”

Don’t want to try this at home?

Here’s an easy way to find your local noon. Visit Sunrise Sunset Calendars to find out the clock time for solar noon (sun on your meridian) in your sky, remembering to check the solar noon box.

Of course, the sun is not the only celestial object to climb highest up for the day when it crosses the meridian at upper transit. The same goes for the moon, planets and stars. But it’s easier to determine your meridian by using the sun.

Bottom line: In the jargon of astronomers, the sun is said to make an upper meridian transit when it reaches its highest point for the day at solar noon (midday).

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