Perihelion is when Earth is closest to the Sun, occurring in January after the winter solstice. The difference between perihelion and aphelion is small due to Earth’s nearly circular orbit. Seasons are determined by Earth’s tilt, not its position. Scientists use predictive formulas to determine the date and time of perihelion. Earth’s regular orbit and mild seasons make it habitable, and planets with similar orbits may also harbor life. Observers on Earth may not notice much difference during perihelion and aphelion.
A perihelion is the point in Earth’s orbit closest to the Sun. The opposite is called aphelion, where the Earth moves farthest away. During perihelion, the Sun’s light tends to be more intense due to the closer proximity. This event typically occurs in January, several weeks after the winter solstice in the Northern Hemisphere. While it might seem like it should be summer for everyone when the Earth is close to the Sun, the seasons are determined by the planet’s tilt, not its position in space.
The difference between perihelion and aphelion is not much, on the scale of the rest of space. At perihelion, the Earth is nearly 92 million miles (about 147.5 million kilometers) from the Sun, while at aphelion it is nearly 95 million miles (about 152.6 million kilometers) away. These relatively small distances are the result of the Earth’s nearly circular orbit around the Sun; in scientific terms, it is said to have a “low eccentricity,” unlike planets like Pluto, which have much more exaggerated elliptical orbits.
The dating can vary from year to year, as the Earth’s orbit around the Sun does not take exactly 365 days. Scientists can calculate the precise date and time of perihelion using predictive formulas and calendar adjustments such as leap years. Periodically it may be necessary to add leap seconds or other time units to compensate for small variations that can add up over long periods of time. They can also use this information to extrapolate backwards to determine the date of perihelion at various points in history.
Researchers can use a variety of instruments to measure the perihelion distance and to determine the intensity of light at the Earth’s surface during this period. Earth’s regular orbit is one reason the plant is habitable, because it doesn’t go through extremes as it moves around the Sun. Seasons are a result of the planet’s off-center tilt, but remain relatively mild. Planets with similar orbital characteristics also have the potential to harbor life and are sometimes targets for research by astronomers.
Observers on Earth may not notice much differently during perihelion and aphelion. The size of the Sun would appear the same, to those who have used tools to see it safely, such as heavily filtered cameras. While sunlight is more intense, the difference isn’t significant enough to be noticed on the ground without specialized instruments.
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