Perihelion: NASA detail astronomical phenomenon
The northern hemisphere remains in winter’s grip, with countries such as the UK facing freezing snowy and icy conditions. So some may be surprised to learn our planet is today actually at its closest point to the Sun for the entire year – a phenomenon known as perihelion.
What is perihelion?
At perihelion, Earth will be about 91.5 million miles from our local star
Perihelion is the precise period when the orbit of Earth approaches its nearest point to our solar system’s star.
The word ‘perihelion’ is derived from the Greek words ‘peri’ – meaning ‘near’ – and ‘helios’ – meaning ‘Sun’.
At 1.51pm GMT on Saturday, January 2, our world is positioned exactly 91,399,453 miles (147,093,162 million km) from the Sun.
This is approximately three percent closer than average, resulting in Earth receiving significantly more radiation as heat from the Sun.
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As a result, the Sun will also be almost-imperceptibly larger in our daytime sky.
US-based space agency NASA said in a statement: “The average distance from Earth to the Sun is called an Astronomical Unit [AU], but since our orbit is not a perfect circle, it means sometimes we’re a bit closer to the Sun, and sometimes farther away.
“In fact, our distance from the Sun varies by around three million miles over the course of the year.
“That’s nearly 13 times the distance from Earth to the Moon.
“At perihelion, Earth will be about 91.5 million miles from our local star.
“And when we’re at the farthest point, it’s called ‘aphelion’.
“That happens this year on July 5, when we’ll be about 94.5 million miles away.”
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What does perihelion mean for you?
Our planet’s proximity to the Sun will not actually impact temperatures to any discernible degree.
Neither temperature, weather or seasons are in fact determined by how close Earth is to the Sun.
All three are instead caused entirely by the tilt of Earth’s axis of rotation.
Current conditions in the northern hemisphere are due to our planet being titled away from the Sun, while the southern hemisphere is titled towards the star.
Earth is known to spin on an axis titled by 23.44 degrees – a leaning responsible for allocating how much sunlight each hemisphere of Earth receives at different times of the year.
This is both in terms of days’ duration and how low or high the Sun hangs in the heavens.
This obliquity is the key factor responsible for the seasons and the solstices.
Somewhat counterintuitively, although perihelion means Earth receives more radiation from the Sun, Earth is in fact at its coolest during this period.
This is because most of the southern hemisphere are oceans, which absorb the extra heat, negating perihelion’s impact.
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