Sunday, January 03, 2021

Perihelion from Arne

Arne Kaare Novik: The Norwegian Benny Hill, stated on Zoom last evening that the earth was closest to the Sun on January 2, 2021.

I looked it up.

NASA's Solar Dynamic Observatory: The Sun

Earth closest to sun on January 2, 2021 Posted by Bruce McClure in tonight | January 1, 2021


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Our planet Earth will reach its closest point to the sun for 2021 on January 2, at 13:51 UTC. In United States time zones, that’s January 2 at 8:51 a.m. Eastern Time, 7:51 a.m. Central Time, 6:51 a.m. Mountain Time, 5:51 a.m. Pacific Time, 4:51 a.m. Alaskan Time and 3:51 a.m. Hawaiian Time. Translate UTC to your time. Astronomers call this celebrated point in Earth’s elliptical orbit around the sun perihelion, from the Greek roots peri meaning near and helios meaning sun.

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At its closest point, Earth swings to within 91,399,453 miles (147,093,162 km) of the sun. That’s in contrast to six months from now, when the Earth reaches aphelion – its most distant point – on July 5, 2021. Then we’ll be 94,510,889 miles (152,100,533 km) from the sun.

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In other words, Earth is roughly 3 million miles (5 million km) closer to the sun in early January than it is in early July. That’s always the case. Earth is closest to the sun every year in early January, when it’s winter for the Northern Hemisphere. We’re farthest away from the sun in early July, during our Northern Hemisphere summer.

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In the Northern Hemisphere, the summer season (June solstice to September equinox) lasts nearly five days longer than our winter season. And, of course, the corresponding seasons in the Southern Hemisphere are opposite. Southern Hemisphere winter is nearly five days longer than Southern Hemisphere summer.


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It is all about the tilt of the Earth’s axis. Many people believe that the temperature changes because the Earth is closer to the sun in summer and farther from the sun in winter. In fact, the Earth is farthest from the sun in July and is closest to the sun in January! 

During the summer, the sun’s rays hit the Earth at a steep angle. The light does not spread out as much, thus increasing the amount of energy hitting any given spot. Also, the long daylight hours allow the Earth plenty of time to reach warm temperatures. 

During the winter, the sun’s rays hit the Earth at a shallow angle. These rays are more spread out, which minimizes the amount of energy that hits any given spot. Also, the long nights and short days prevent the Earth from warming up. Thus, we have winter!
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Admittedly, I am not a scientist, but I had learned, I think in grade school, that the earth's tilt and axis determined the seasons in the Northern and Southern Hemispheres.

Oxford Dictionary of Science, (2010), Sixth Edition, Oxford, Oxford University Press.

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Perihelion

The point in the solar orbit of a planet, comet, or other solar system object, natural or artificial, at which it is nearest to the sun. (609). 

This text states that in the 21st century, the perihelion is on or about January 3. (609).

Aphelion, is defined in the same way in Oxford, but is when the earth is farthest from the sun. (50). In the 21st century, it is on or about July 4. (50).

Notice the slight difference in the dates provided from sources...