‘Perihelion Day' Is When Earth Is Closest to the Sun — so Why Is It So Cold?
On “Perihelion Day,” our planet makes its annual closest approach to the sun. The night of January 4 marks the exact time when Earth is closest to our star, but unfortunately, being closer to the sun doesn’t necessarily mean that we’ll see warmer temperatures.
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When is perihelion?
Earth’s annual closest approach to the sun takes place at precisely 7:48 Universal Time on January 5, 2020. That’s 2:48 a.m. EST on January 5 and 11:48 p.m. PST on January 4. At that time, our planet will be within just 91,398,199 miles of the sun. It always happens a couple of weeks after the December solstice, when the Northern Hemisphere is tilted away from the sun.
What is perihelion?
The word comes from the Greek words peri (near) and helios (sun). It happens because Earth’s orbit of the sun is slightly elliptical, so there are naturally two points during a complete orbit — one year — when it’s closest and farthest away.
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So, why is it so cold?
It’s all about the tilt. Earth’s axis is tilted 23° relative to its orbit around the sun, a phenomenon that causes the seasons. When the Northern Hemisphere is tilted away from the sun, it suffers winter. That tilt puts the sun lower in the Northern Hemisphere’s sky, making sunlight less intense and shortening the day. When the Northern Hemisphere is tilted away from the sun, the Southern Hemisphere is tilted towards it, so it experiences summer weather during this period! It’s just never going to be that warm north of the equator during winter.
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Is the planet at its warmest around perihelion?
It might seem logical to think that temperatures would rise when Earth is closest to the sun. In reality, Earth is at its coolest at perihelion! That’s because rocks heat up much more quickly than water. Most of the landmass on Earth is in the Northern Hemisphere, and most of the Southern Hemisphere is ocean. Any extra sunlight the Earth gets at perihelion is soaked up by the oceans, so it doesn’t really have much effect.
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What is aphelion?
It’s the exact opposite to perihelion. It marks the day when Earth is farthest from the sun, which is always on or very close to July 4, about two weeks after the June solstice. At that most distant point, Earth will be 94,507,635 miles from the sun. However, even though the sun is a little weaker, the rocky Northern Hemisphere heats up easily, so you can expect sweltering temperatures (even though we’re farther from the sun).
Just like our own trips, Earth’s incredible path around the sun is all about the journey, not the destination.
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