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As Earth orbits the Sun, it undergoes four distinct seasons. During this journey, the length of daylight grows for the six months between the winter and summer solstices, and it shrinks in the opposite direction from summer to winter. Earth also spins on its axis in a 24-hour cycle, while the Moon completes its orbit around Earth every 28 days. These cycles continue without end, but many nuances hidden within them remain unnoticed, unexplained, or simply unknown to most people.
10. Peak Moment
Fact: The Sun does not always reach its highest point at noon.
The time at which the Sun reaches its highest point in the sky (true noon) shifts throughout the year. This occurs due to two factors: Earth's orbit is elliptical, not circular, and the planet is tilted in relation to the Sun. While Earth's rotation speed is nearly constant, the Earth orbits faster at certain times of the year, causing the rotation to sometimes lead or lag behind its respective orbital position in a circular orbit. The impact of Earth's tilt can be visualized by imagining a circle of points along the equator. If you tilt this circle by 23.44 degrees (the current value of Earth's obliquity), all points except those on the equator and tropics will experience a change in longitude. Additionally, there is a shift in the time the Sun reaches its peak position in the sky, depending on the observer's geographic longitude, but this effect remains constant for each longitude.
9. Sun’s Rise Direction
Fact: The direction of sunrise and sunset does not change immediately during the solstices.
Many believe that, in the northern hemisphere, the Sun sets earliest on the December solstice and latest on the June solstice. However, this is a misconception. The solstices mark the days when daylight length is at its longest or shortest. The change in true noon shifts both sunrise and sunset times accordingly. At the December solstice, true noon becomes later at a rate of 30 seconds per day. Since there is no immediate change in daylight at the solstices, both sunset and sunrise continue to get later at the same rate. As a result, the earliest sunset has already passed, and the latest sunrise has yet to occur. Similarly, the latest sunset happens shortly after the summer solstice, and the earliest sunrise occurs shortly before it. The difference, however, is less pronounced than during the December solstice because the shift in noon caused by Earth's eccentricity at the summer solstice offsets the change caused by Earth's tilt (which is positive at both solstices), but the total rate of change remains positive.
8. Earth’s Oval-Shaped Orbit
While most people know that Earth orbits the Sun in an elliptical path rather than a perfect circle, the eccentricity of Earth's orbit is roughly 1/60. Planets in periodic orbits around their stars always have an eccentricity value between 0 and 1, including 0 but excluding 1. An eccentricity of 0 represents a perfectly circular orbit with the Sun at the center, and the planet traveling at a constant speed. Such an orbit is highly unlikely, as there are infinite possible eccentricity values. Eccentricity in a closed orbit is calculated by dividing the distance from the Sun to the center of the ellipse by the length of the semi-major axis. The orbit grows longer and narrower as the eccentricity approaches 1. A planet always moves fastest when closest to its Sun and slowest when farthest from it. If the eccentricity reaches or exceeds 1, the planet completes one orbit around its Sun and then flies off into space, never to return.
7. Earth’s Wobble
The Earth experiences periodic wobbles, a phenomenon known as nutation. This wobble is primarily caused by external gravitational forces acting on Earth’s equatorial bulge. Both the Sun and the Moon exert forces on this bulge, causing the Earth to wobble. However, these effects are insignificant for casual astronomical observations. Earth's tilt and longitude follow a cycle of 18.6 years, which is the time it takes for the Moon to complete its orbit through its nodes, along with smaller wobbles of six months and two weeks, attributed to Earth's orbit around the Sun and the Moon's orbit around Earth, respectively.
6. The Flat Earth Theory
Fact (sort of): Earth is indeed flat.
Perhaps the Catholics during Galileo’s time were not entirely wrong in believing that Earth was flat. In fact, Earth is nearly spherical, but it is slightly flattened at the poles. The equatorial radius is 6378.14 kilometers, while the polar radius measures 6356.75 kilometers. This shape led geologists to develop different types of latitude measurements. Geocentric latitude defines latitude as an angle between the equator and Earth's center, while geographic latitude defines it based on an angle from the equator straight down beneath the observer. Geographic latitude is the standard for map plotting and coordinate identification. However, the Earth-Sun declination, which determines how far north or south the Sun shines on Earth at different times of the year, is always measured using geocentric latitude values.
5. Precession Effect
The Earth’s axis rotates slowly, much like a top. In addition, the ellipse that forms Earth’s orbit gradually shifts, causing the shape Earth traces around the Sun over many years to resemble a daisy. As a result of these two types of precession, astronomers have identified three distinct types of years: the sidereal year (365.256 days), which represents one full orbit relative to distant stars; the anomalistic year (365.259 days), which is the time it takes for Earth to travel from its closest point (perihelion) to its farthest point (aphelion) and back; and the tropical year (365.242 days), which is the period between one spring equinox and the next.
4. Milankovitch Cycles
In the early 20th century, astronomer Milutin Milankovitch uncovered that the Earth’s tilt (obliquity), orbital shape (eccentricity), and axis rotation (precession) are not fixed. Over roughly 41,000 years, the Earth’s tilt gradually shifts from 24.2–24.5 degrees to 22.1–22.6 degrees, and then back again. Presently, the Earth’s axial tilt is on a decrease, and we are approximately halfway to reaching the minimum of 22.6 degrees, which is expected to occur around the year 12,000. The Earth’s eccentricity follows a more erratic cycle with a period of 100,000 years. It fluctuates between 0.005 and 0.05, and as noted in point 8, it’s currently 1/60 or 0.0166 but is slowly decreasing. It is predicted to reach about 0.006 by the year 28,000. Milankovitch hypothesized that these cycles contribute to the onset of ice ages. When both the Earth’s tilt and orbital eccentricity are extreme, and the precession causes the Earth to be directly tilted away from or toward the Sun at aphelion, this can result in harsh winters and excessive ice accumulation, which doesn’t fully melt in spring or summer.
3. Seasonal Delay
You might observe that the solstices and equinoxes mark the beginning of their respective seasons, not their midpoints. This happens because Earth needs time to warm up or cool down, meaning the seasons lag behind the changing daylight lengths. This phenomenon is called seasonal lag, and its duration depends on where you are located geographically. The further you are from the equator, the smaller the lag tends to be. For example, in many cities in North America, the seasonal lag is about a month, with the coldest weather arriving around January 21 and the warmest around July 21. For instance, by the end of August, you might still be enjoying the last warm days of summer, dressing lightly, or taking one last trip to the beach. However, on the opposite side of the summer solstice, with the same daylight duration, it would be roughly April 10, a time when most people wouldn't even be thinking about summer yet.
2. The Moon is Drifting Away
Each year, the Moon drifts about 4 centimeters (1.6 inches) farther from the Earth as a result of the tidal forces it generates. The Moon’s gravitational pull causes a slight distortion in the Earth's crust, shifting it by several centimeters. As the Moon orbits the Earth much faster than it rotates, this bulge in the Earth’s crust causes the Moon to move ahead of its orbit, gradually pulling it away from the Earth.
1. Slowing Rotation
Friction from tidal forces and interstellar particles is slowly decelerating the Earth’s rotation. On average, Earth’s day lengthens by about one five-hundredth of a second each century. In the distant past, when the Earth was still in its formative stages, days were much shorter, lasting only 13 or 14 hours instead of the present 24. This gradual slowing is why we occasionally add a leap second to our clocks. However, the time when a 24-hour day will no longer suffice is so far in the future that we can only speculate on the solutions. Some predict that we might need to extend each day by an extra unit of time, possibly leading to 25-hour days, or adjust the length of the hour to accommodate longer days, splitting them into 24 equal parts.
