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Orbit of Earth


On average, Earth is 150 million km from the Sun. However, Earth’s path around the Sun travels an elliptical orbit. This means there are times when Earth is closer, and times that it’s further.

The closest point of this elliptical orbit is called the perihelion. At this point, Earth is only 147 million km from the Sun.

At its furthest point, which astronomers call aphelion, Earth is 152 million km.

You can see there’s a significant different between these two points. And this can actually vary the amount of sunlight that reaches our planet. The perihelion happens in January, when the northern hemisphere is tilted away from the Sun, and experiencing Winter. The southern hemisphere is tilted towards the Sun, and experiencing Summer.

Since there’s 6.9% more solar energy hitting Earth, you would think that southern summers should really be much hotter, but they aren’t. Scientists think that the increased amount of oceans in the southern hemisphere are able to absorb this extra sunlight, and keep northern and southern temperatures roughly equivalent.

Earth takes 365.256 days to complete one orbit around the Sun. That extra .256 of a day is why we have leap years. For every year divisible by 4, we have a February 29th. Unless that year is divisible by 100 (like the year 1900), unless that year is divisible by 400 – that’s why there was a leap year in the year 2000.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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