Is the Earth's rotation slowing down?

Yes. About 400 million years ago, there were 400 days a year, versus the present day 365. Eventually, if the Sun doesn't die first, the Earth will stop rotating completely.

Does the Earth's tilt ever change?

Yes. Our planet actually wobbles a bit, like a spinning top running out of steam. Currently, the "axial tilt" of our planet is about 23.5 degrees, which is somewhere in the middle of its total capable range of 22.1 to 24.5 degrees. The change in tilt occurs over a period of about 41,000 years.

What is precession?

Precession is a phenomenon that results from the planet's changing tilt. You can think of it as a kind of wobbling effect. About 12,900 years from now, the North Pole will be tilted toward the Sun in January and away from it in June. This means that the winter season in the North will occur during the months that are now considered summer (late June through early September) and summer will occur from January through March. This change will be gradual over time, and no one alive today or for many generations will be aware of it.

What is orbital inclination?

Not only does our planet tilt back and forth and wobble while it's doing it, but it also ranges up and down relative to the invariable plane (the plane, in simplified terms, passing through the solar system's center of mass). If you imagine the Earth's orbit as forming a disk like a CD, then imagine the CD wobbling back and forth instead of spinning on a level plane (formed by the invariable plane), then you might get the idea of orbital inclination. The current orbital inclination of the Earth causes it to pass through the invariable plane in early January and early July. The invariable plane carries with it more space dust and debris than is found above and below this plane; thus, as the Earth passes through the invariable plane, the atmosphere comes in contact with more space dust, which means we see more meteor showers and meteorites. The space dust also contributes to cloud formation in the upper atmosphere: noctilucent clouds.

What is the difference between perihelion and aphelion?

Perihelion is the point where the Earth is closest to the Sun (91.4 million miles, or 147 million kilometers). This occurs around January 3 every year. Aphelion is when

This old chart explains how Earth

This old chart explains how Earth's orbit tilt results in the seasons, as well as how eclipses are formed, the phases of the Moon, and the latitudinal zones.

our planet reaches its farthest point from the Sun (94.5 million miles, or 152 million kilometers) around July 4. This variation does not have much effect on weather patterns or seasons.

What are solstices and when do they occur?

A solstice is a time of the year when Earth is pointed either the closest toward the Sun or the farthest away from it. On the summer solstice, there are more minutes

Archeologists generally agree that ancient Stonehenge near Wiltshire, England, was used long ago to mark solstices and equinoxes.

Archeologists generally agree that ancient Stonehenge near Wiltshire, England, was used long ago to mark solstices and equinoxes.

of daylight than there are on any other day of the year; on the winter solstice, there are fewer minutes of daylight than there are on any other day of the year. In the northern hemisphere, the summer solstice occurs around June 21 of each year, when the North Pole is pointed closest toward the Sun, and the winter solstice occurs around December 21 of each year, when the North Pole is pointed farthest away from the Sun.

What are equinoxes and when do they happen?

An equinox is a time of the year when, in the course of Earth's orbit, our planet is at a location where the equatorial plane and the ecliptic plane intersect. In other words, the tilt of Earth's axis is pointed perpendicular to the line between Earth and the Sun at an equinox—Earth's poles are tilted neither "toward" nor "away" from the Sun, but tilted off to the "side." On the day of an equinox, there are as many minutes of daylight as there are of night—hence the term "equinox," meaning "equal darkness." In the northern hemisphere, the vernal (spring) equinox occurs around March 21 of each year, and the autumnal (fall) equinox occurs around September 21.

 
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