# When is the first sunrise and the last sunset of the year?

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With a great amount of atmosphere to cross, the sunlight (or the moon) becomes tremendously reddish when it is near the horizon. Neither the last sunset of the year nor the first sunrise of the year corresponds to the summer solstice.

Max Pixel / FreeGreatPicture.com

The duration of a day on planet Earth may always look the same at 24 hours, but the amount of light we receive changes dramatically throughout the year. The summer solstice gives us the greatest amount of light of day, with the most polar latitudes passing through the longest days. If you are near the equator, however, there is no difference between the number of hours the sun passes in the sky throughout the year, from the summer solstice to the equinox, winter solstice and vice versa. determine everything about the length of a day, and that is what Sponsor Ben Turner wants to know, asking,

We all know that solstices are the longest / shortest days of the year, but given the analemma, when are the first / most recent times of sunrise / sunset? Is it consistent across all latitudes?

It's not consistent and it's a very complicated story. Let's explore why.

As the Earth rotates about its axis and orbits the Sun in an ellipse, the apparent position of the Sun seems to change from day to day in this particular form: the earth's analema. The slope of the analemma will correspond to the time of day when the image is taken, but this shape is always reproduced from the Earth if you take a picture at the same time every day.

Giuseppe Donatiello / flickr

This is the analemma: the form you get if you take a picture of the sun every day during the year from the same spot at the same time of day. This particular analema was withdrawn from the Earth's northern hemisphere, and was taken some time during the afternoon. You can say this from the form and orientation of the analemma. From the northern hemisphere, the little loop of this figure-8 is always higher; from the south, the larger loop is at the top.

If you were to photograph the analemma at noon, when the sun reached its highest angular height above the horizon, the analemma would be completely vertical, while it would rotate counterclockwise at the beginning of the day and clockwise at the end of the day. In all cases, the summer solstice is the tip of the long axis of the analemma, while the winter solstice lies at the opposite end.

Even though the Earth always rotates on its axis, which is inclined to 23.5 degrees, the equinoxes are special so that the axial slope is perpendicular to the Sun-Earth plane, and not at an angle, which occurs on all other days of the year . Similarly, the solstices are what occurs at midpoints between the equinoxes: when the Earth's axis is tilted to the maximum relative to the Earth's orbital plane around the Sun. The elliptical nature of our orbit is extremely important.

Larry McNish / RASC Calgary Center

The reason why the analemma has the particular form it does is due to two factors working in combination:

1. the Earth is inclined at its axis, at 23.5 ° deg. in relation to the Earth's orbital plane, as it rotates,
2. and the Earth moves around the Sun in an elliptical form instead of a perfect circle.

If the Earth's axis were not tilted as it rotated, and our planet also orbited in a perfect circle around the Sun, our analemma would be merely a single point: the Sun would follow the same path every day. With each passing day, our planet would run a total of 360 & deg; in 23 hours and 56 minutes, and then spend an extra 4 minutes to "reach" the previous position of the Sun in the sky, since we are also revolving around the Sun. This extra 4 minutes is because our days are 24 hours: because we have to rotate more than 360 & deg; to complete an entire day.

Traveling once around the orbit of the Earth on a path around the Sun is a journey of 940 million kilometers. The extra 3 million kilometers that Earth travels through space per day ensures that 360-degree rotation on our axis will not restore the Sun to the same relative position in day-to-day sky. That's why our day takes more than 23 hours and 56 minutes, which is the time required to rotate 360 ​​degrees.

Larry McNish at the RASC Calgary Center

When we realize that this is how the Solar System works, we can begin to add the other effects. Our planet is tilted on its axis, which means that the path of the Sun through the sky will change throughout the year. When you compare the solstice of June with the solstice of December, the difference in the apparent position of the Sun will differ by two times our axial inclination: 47 & deg; If you examined the top-down angular range of our analemma, through its long axis, you would discover that it was 47 & deg; in heaven from all places of the earth.

If our planet were just tilted, but still orbited in a perfect circle, our analemma would be a perfectly symmetrical figure-8. Both wolves of the "8" would be symmetrical, and they would cross in the middle: during the equinoxes. In the spring and autumn, after the equinoxes, the sun increased and set after the average, while in summer and winter, after the solstices, the sun increased and set before the average.

The effect of the elliptical nature of our (left) orbit and our axial (mean) inclination at the position of the Sun in the sky combine to create the form of analema (right) we observe from planet Earth.

Image generated by Autodesk via UK

But eccentricity adds another effect. When the Earth is farther from the Sun (closer to the aphelion), it orbits the Sun more slowly than the average, so that our planet advances more than it needs in a period of 24 hours. When the Earth is closer to the Sun (near the perihelion), it orbits faster than the average, then our planet spins a little less than necessary to return the Sun to the same exact position after 24 hours.

Due to this effect, and to the fact that perihelion occurs shortly after the December solstice (with aphelion occurring shortly after the June solstice), the "December Solstice" side of the analemma is much larger, with greater time differences , while the "Solstice of June" side is much narrower, with smaller deviations from the average time. There is constructive interference of these two effects during the end of the year, but destructive interference during the middle of the year.

The equation of time is determined by both the shape of a planet's orbit and its axial inclination, and by the way it aligns. During the months closest to the solstice of June (when Earth approaches aphelion, its position farthest from the Sun), it moves more slowly, and that is why this section of the analemma is compressed, while the December solstice, near the perihelion, is elongated. .

Wikimedia Commons has media related to: Rob Cook

O equation of time, which is the combined effect of our revolution around the Sun and its orbital eccentricity with the effect of our rotation and axial inclination, is the same in all latitudes of Earth. When we are close to the June solstice, everything is sooner.

In the northern hemisphere, although the days are longer, sunrise and sunset are shifted to somewhat earlier times at earlier dates. Someone close to the Arctic Circle will see their first sunrise occur 1-3 days before the solstice, while someone in mid-latitudes (around Washington, DC) receives it about a week before solstice, and someone near the Tropic of Cancer . It gets the first sunrise about two weeks before the solstice. In the southern hemisphere, similar changes occur in a latitude-dependent manner, except that this gives it its oldest sunset, as the days are shorter.

Pan-STARRS2 and PanSTARS1 telescopes on top of Haleakala on Maui Island, Hawaii, whose data were instrumental in mapping the dust of the Milky Way. The first and most recent sunrises and sunsets at the top of Mauna Kea, near the Tropic of Cancer, will be displaced from the solstice for several weeks.

Pan-STARRS Collaboration

Likewise, because of the way the equation of time changes (where the signal changes very close to each solstice), the late-time observer of the northern hemisphere sees the same latitude dependent deviations except after the June solstice. Near the Arctic Circle, the most recent sunset occurs 1-3 days after the solstice; Average latitudes see their most recent sunset about a week after the solstice; Tropic of latitudes similar to cancer gets its most recent sunset around the 4th of July.

In the southern hemisphere, similar changes occur in the same manner dependent on latitude. The big difference is that you will have your last dawns of the year at those times.

The Earth in orbit around the Sun, with its rotational axis shown. All the worlds of our solar system have stations determined by their axial inclination, the ellipticity of their orbits or a combination of both.

Wikimedia Commons user Tau'olunga

What is interesting about all this is that what the northern and southern hemisphere experiences during the June solstice is not exactly reversed during the December solstice. As the time equation has much more pronounced changes when the effects of obliquity and ellipticity interfere constructively, the time shifts are larger around the December solstice than at the June solstice.

This is something you may have guessed by observing the form of the analemma. On the side where the lobe of Figure 8 is larger and the greatest time differences, you can expect that the sunset / sunrise times are shifted in a larger amount than where the wolf of Figure-8 is smaller. The great wolf, corresponding to the December solstice, sees much more dramatic changes.

If you photograph the sun every day at noon, your analemma appears perfectly vertically (left). Before midday (upper right), the analemma appears to rotate counterclockwise toward the horizon, while after midday, it appears to rotate clockwise relative to the horizon. These images are yet another proof, to any dubious out there, that the Earth is round.

The Sydney Morning Herald

As a result, you need not just reverse the hemispheres and sunrise / sunset effects from June to December, but the combined effects of obliquity and ellipticity increase the sunrise / sunset start / end effects in approximately 50%. When planet Earth approaches the Sun, its movement is significantly faster than at any other time, which means that we experience great changes in how much our clocks start from an astronomical clock. "average time" between sunrise and sunset.

There are two other points where the time equation returns to a symmetrical state: on April 14 and August 30. These points, about 3 weeks after the March equinox and 3 weeks before the September equinox, have no special significance. They are determined by the way our stations, determined by the axial inclination, align with the orbit of our planet around our Sun.

Over a year of 365 days, the Sun seems to move not only up and down in the sky, as determined by our axial inclination, but forward and backward, as determined by our elliptical orbit around the Sun. When both effects are combined, the resulting compressed figure 8 is known as an analemma. The images of the Sun shown here are 52 photographs selected from the observations of the C & in Mexico, over a calendar year.

C & eacute; It is not / AstroColors

The form of our analemma and the equation of Earth's time are not fixed. Approximately 5,000 years from now, the perihelion and aphelion of our planet will be aligned with our equinoxes, which means that our analemma will change from a form of figure 8 to a teardrop shape.

When this alignment reaches perfection, in our relatively distant future, our sunrise and the last sunset will occur on the summer solstice, and our last sunrise and first sunset will occur on the winter solstice. Although the specific times in which these events occur vary by latitude, all will occur on the same dates for all observers on Earth. As we precess the axis of our planet, which must continue longer than our sun shines, our sunset and sunrise times will continue to change from year to year. Thanks to our axial inclination and elliptical orbit, we can finally understand how.

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With a great amount of atmosphere to cross, the sunlight (or the moon) becomes tremendously reddish when it is near the horizon. Neither the last sunset of the year nor the first sunrise of the year corresponds to the summer solstice.

Max Pixel / FreeGreatPicture.com

The duration of a day on planet Earth may always look the same at 24 hours, but the amount of light we receive changes dramatically throughout the year. The summer solstice gives us the greatest amount of light of day, with the most polar latitudes passing through the longest days. If you are near the equator, however, there is no difference between the number of hours the sun passes through the sky throughout the year, from the summer solstice to the equinox, to the winter solstice, and vice versa. But the solstices do not determine everything to a day's length, and that's what Patreon's supporter, Ben Turner, wants to know, asking,

We all know that solstices are the longest / shortest days of the year, but given the analemma, when are the first / most recent times of sunrise / sunset? Is it consistent across all latitudes?

It's not consistent and it's a very complicated story. Let's explore why.

As the Earth rotates about its axis and orbits the Sun in an ellipse, the apparent position of the Sun seems to change from day to day in this particular form: the earth's analema. The slope of the analemma will correspond to the time of day when the image is taken, but this shape is always reproduced from the Earth if you take a picture at the same time every day.

Giuseppe Donatiello / flickr

This is the analemma: the form you get if you take a picture of the sun every day during the year from the same spot at the same time of day. This particular analema was withdrawn from the Earth's northern hemisphere, and was taken some time during the afternoon. You can say this from the form and orientation of the analemma. From the northern hemisphere, the little loop of this figure-8 is always higher; from the south, the larger loop is at the top.

If you were to photograph the analemma at noon, when the sun reached its highest angular height above the horizon, the analemma would be completely vertical, while it would rotate counterclockwise at the beginning of the day and clockwise at the end of the day. In all cases, the summer solstice is the tip of the long axis of the analemma, while the winter solstice lies at the opposite end.

Even though the Earth always rotates on its axis, which is inclined to 23.5 degrees, the equinoxes are special so that the axial slope is perpendicular to the Sun-Earth plane, and not at an angle, which occurs on all other days of the year . Similarly, the solstices are what occurs at midpoints between the equinoxes: when the Earth's axis is tilted to the maximum relative to the Earth's orbital plane around the Sun. The elliptical nature of our orbit is extremely important.

Larry McNish / RASC Calgary Center

The reason why the analemma has the particular form it does is due to two factors working in combination:

1. the Earth is inclined on its axis, 23.5 ° in relation to the orbital plane of the Earth, as it rotates,
2. and the Earth moves around the Sun in an elliptical form instead of a perfect circle.

If the Earth's axis were not tilted as it rotated, and our planet also orbited in a perfect circle around the Sun, our analemma would be merely a single point: the Sun would follow the same path every day. With each passing day, our planet rotated 360 ° in 23 hours and 56 minutes, and then spent 4 extra minutes to "reach" the previous position of the Sun in the sky, as we are also spinning around the sun. That extra 4 minutes is why our days are 24 hours: because we have to rotate more than 360 ° to complete a whole day.

Traveling once around the orbit of the Earth on a path around the Sun is a journey of 940 million kilometers. The extra 3 million kilometers that Earth travels through space per day ensures that 360-degree rotation on our axis will not restore the Sun to the same relative position in day-to-day sky. That's why our day takes more than 23 hours and 56 minutes, which is the time required to rotate 360 ​​degrees.

Larry McNish at the RASC Calgary Center

When we realize that this is how the Solar System works, we can begin to add the other effects. Our planet is tilted on its axis, which means that the path of the Sun through the sky will change throughout the year. When you compare the solstice of June with the solstice of December, the difference in the apparent position of the Sun will differ twice from our axial inclination: 47 °. If you looked at the angular scale from the top downward of our analemma through its long axis, you would find that it was in the sky at 47 ° from each place on Earth.

If our planet were just tilted, but still orbited in a perfect circle, our analemma would be a perfectly symmetrical figure-8. Both lobes of the "8" would be symmetrical and would cross in the middle: during the equinoxes. In the spring and autumn, after the equinoxes, the sun increased and set after the average, while in summer and winter, after the solstices, the sun increased and set before the average.

The effect of the elliptical nature of our (left) orbit and our axial (mean) inclination at the position of the Sun in the sky combine to create the form of analema (right) we observe from planet Earth.

Image generated by Autodesk via UK

But eccentricity adds another effect. When the Earth is farther from the Sun (closer to the aphelion), it orbits the Sun more slowly than the average, so that our planet advances more than it needs in a period of 24 hours. When the Earth is closer to the Sun (near the perihelion), it orbits faster than the average, then our planet spins a little less than necessary to return the Sun to the same exact position after 24 hours.

Due to this effect, and to the fact that perihelion occurs shortly after the December solstice (with aphelion occurring shortly after the June solstice), the "solstice of December" side of the analemma is much larger, with greater time differences , while the "solstice of June". "side is much narrower, with smaller deviations from mean time. There is constructive interference of these two effects during the end of the year, but destructive interference during mid-year.

The equation of time is determined by both the shape of a planet's orbit and its axial inclination, and by the way it aligns. During the months closest to the solstice of June (when Earth approaches aphelion, its position farthest from the Sun), it moves more slowly, and that is why this section of the analemma is compressed, while the December solstice, near the perihelion, is elongated. .

Wikimedia Commons has media related to: Rob Cook

The equation of time, which is the combined effect of our revolution around the Sun and its orbital eccentricity with the effect of our rotation and axial inclination, is the same in all latitudes of Earth. When we are close to the June solstice, everything is sooner.

In the northern hemisphere, although the days are longer, sunrise and sunset are shifted to somewhat earlier times at earlier dates. Someone close to the Arctic Circle will see their first sunrise occur 1-3 days before the solstice, while someone in mid-latitudes (around Washington, DC) receives it about a week before solstice, and someone near the Tropic of Cancer . It gets the first sunrise about two weeks before the solstice. In the southern hemisphere, similar changes occur in a latitude-dependent manner, except that this gives it its oldest sunset, as the days are shorter.

Pan-STARRS2 and PanSTARS1 telescopes on top of Haleakala on Maui Island, Hawaii, whose data were instrumental in mapping the dust of the Milky Way. The first and most recent sunrises and sunsets at the top of Mauna Kea, near the Tropic of Cancer, will be displaced from the solstice for several weeks.

Pan-STARRS Collaboration

Likewise, because of the way the equation of time changes (where the signal changes very close to each solstice), the late-time observer of the northern hemisphere sees the same latitude dependent deviations except after the June solstice. Near the Arctic Circle, the most recent sunset occurs 1-3 days after the solstice; Average latitudes see their most recent sunset about a week after the solstice; Tropic of latitudes similar to cancer gets its most recent sunset around the 4th of July.

In the southern hemisphere, similar changes occur in the same manner dependent on latitude. The big difference is that you will have your last dawns of the year at those times.

The Earth in orbit around the Sun, with its rotational axis shown. All the worlds of our solar system have stations determined by their axial inclination, the ellipticity of their orbits or a combination of both.

Wikimedia Commons user Tau'olunga

What is interesting about all this is that what the northern and southern hemisphere experiences during the June solstice is not exactly reversed during the December solstice. As the time equation has much more pronounced changes when the effects of obliquity and ellipticity interfere constructively, the time shifts are larger around the December solstice than at the June solstice.

This is something you may have guessed by observing the form of the analemma. On the side where the lobe of Figure 8 is larger and the greatest time differences, you can expect that the sunset / sunrise times are shifted in a larger amount than where the wolf of Figure-8 is smaller. The great wolf, corresponding to the December solstice, sees much more dramatic changes.

If you photograph the sun every day at noon, your analemma appears perfectly vertically (left). Before midday (upper right), the analemma appears to rotate counterclockwise toward the horizon, while after midday, it appears to rotate clockwise relative to the horizon. These images are yet another proof, to any dubious out there, that the Earth is round.

The Sydney Morning Herald

As a result, you need not just reverse the hemispheres and sunrise / sunset effects from June to December, but the combined effects of obliquity and ellipticity increase the sunrise / sunset start / end effects in approximately 50%. When planet Earth approaches the Sun, its movement is significantly faster than at any other time, which means that we experience great changes in how much our clocks start from an astronomical "average time" between sunrise and sunset.

There are two other points where the time equation returns to a symmetrical state: on April 14 and August 30. These points, about 3 weeks after the March equinox and 3 weeks before the September equinox, have no special significance. They are determined by the way our stations, determined by the axial inclination, align with the orbit of our planet around our Sun.

Over a year of 365 days, the Sun seems to move not only up and down in the sky, as determined by our axial inclination, but forward and backward, as determined by our elliptical orbit around the Sun. When both effects are combined, the resulting compressed figure 8 is known as an analemma. The images of the Sun shown here are selected from 52 photographs of César Cantú's observations in Mexico during a calendar year.

César Cantú / AstroColors

The form of our analemma and the equation of Earth's time are not fixed. Approximately 5,000 years from now, the perihelion and aphelion of our planet will be aligned with our equinoxes, which means that our analemma will change from a form of figure 8 to a teardrop shape.

When this alignment reaches perfection, in our relatively distant future, our sunrise and the last sunset will occur on the summer solstice, and our last sunrise and first sunset will occur on the winter solstice. Although the specific times in which these events occur vary by latitude, all will occur on the same dates for all observers on Earth. As we precess the axis of our planet, which must continue longer than our sun shines, our sunset and sunrise times will continue to change from year to year. Thanks to our axial inclination and elliptical orbit, we can finally understand how.