Aphelion

Source: UniverseSpaceTech

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Context: Earth reaches aphelion every July, and this year it occurs on Friday at 1:06 a.m. Eastern time.

Details

Earth rotates in an elliptical orbit around the Sun 

• The orbit of the Earth around the sun is elliptical and not circular. Due to this, the distance between the Earth and the sun keeps changing. 
• When this distance is minimum, the Earth is said to be in perihelion(around January 3), When the distance is the maximum, it is said to be in aphelion (around July 4). 
• The Earth’s axis points constantly to the same point (the polar star) in the celestial sphere.
• As a consequence, the latitude on the surface of the earth at which the sun’s rays fall vertically keeps changing as the earth moves its orbit around the sun. Due to this, the earth attains four critical positions with reference to the sun. 
  • Equinoxes: Equinox refers to a day with an equal duration of day and night. We have two equinoxes in a year which are:
    • Spring equinox on March 20
    • Autumnal equinox on September 22
  • Solstice: solstice refers to a day with either the longest day or the shortest. The two solstices in a year are:
    • Winter solstice on December 22
    • Summer solstice on June 21

Cause of aphelion and Perihelion

• That Earth has an aphelion is a result of its orbit being elliptical, rather than circular.

Eccentricity

• How much an orbit deviates from a perfect circle is measured by its eccentricity.
• The higher the eccentricity, the more elliptical the orbit.
• Mars, with an eccentricity of 0.094, ranges from 129 to 155 million miles away from the sun.
• Pluto, whose distance from the sun varies from 2.8 to 4.5 billion miles, is even more eccentric at 0.244.
• Earth has an eccentricity of only 0.017.

Effect of apehelion and perihelion.

• Earth get 7% less sunlight at aphelion compared to what perihelion, leading to slightly milder summers and winters in the Northern Hemisphere.
• At aphelion, which occurs after a solstice, the northern half of the planet is leaning toward the sun, resulting in the longer, hotter days of summer even though Earth is farther away.
• And at perihelion in January, the Northern Hemisphere tilts away from the sun, making the days shorter and the temperatures colder.
• In the Southern Hemisphere, this impact is reversed. Because the hemisphere leans away from the sun when Earth is at aphelion, southern winters are a little cooler than they would be if our orbit were perfectly circular.
• Then as the planet approaches perihelion in January, the hemisphere’s lean toward the sun, making southern summers slightly warmer.
• For planets with more exaggerated eccentricities, the changing distance can have a bigger impact. Sunlight on Mars, for example, can vary as much as 31 percent along its orbit.

Earth Eccentricity and Apehelion

• Earth reaches aphelion close to when its tilt toward the sun is greatest. And this will eventually change, as other planets in the solar system gravitationally yank and squeeze Earth’s orbit in the future.
• Its eccentricity is currently decreasing, meaning its path around the sun is becoming more circular.

What would happen if there were no aphelion?

• If our planetary orbit were a perfect circle, the seasons’ lengths would be exactly the same — presently, spring and summer are a few days longer than fall and winter in the Northern Hemisphere.
• If Earth’s orbit grow more eccentric seasons in the Southern Hemisphere would become too extreme — summers would be unbearably hot, and winters would be intolerably cold. This could lead to crop failures and freezes.

Sources:

NewYorkTimes.

PRACTICE QUESTION Q. Which of the following statements is/are correct? 1. The earth is nearest to the Sun at Perihelion, which generally occurs on January 3. 2. The earth is farthest away from the Sun at Perihelion, which generally occurs on July 4. 3. The earth is farthest away from the Sun at Aphelion, which generally occurs on July 4. 4. The earth is nearest to the Sun at Aphelion, which generally occurs on January 3. Select the correct answer using the code given below: A.1 only B.2 and 4 C.1 and 3 D.1 and 2 Answer C