Sun Farthest from Earth

Sun is far away and still its hot summer in the northern hemisphere. This is the question many have, relating to the distance to the Sun and seasons on earth. The seasons on earth is due to the tilt of the earth at 23.5 degrees. Due to this tilt northern and southern hemispheres are exposed to the Sun during certain months of the year. While Northern hemisphere is exposed to more sun during March to September, the Southern hemisphere will be going through winter and situation reverses after September. From September to March Southern hemisphere is exposed to more Sun and it will be Summer in southern hemisphere while northern hemisphere will be experiencing winter. This is how seasons change on earth.

Earth Tilt and Seasons Credit:CC

Earth makes one full revolution of the Sun in approx 365.256 days. In this orbit around the Sun there are two points where the Sun and earth are closest, called Perihelion, and the other point is the farthest distance between Sun and earth and this point is called Aphelion. The two points Perihelion and Aphelion exists because the orbit of earth around the Sun is not a circular one, it orbits in an elliptical orbit but the difference is very small at an eccentricity of 0.0167. This small elliptical orbit makes the earth”s perihelion distance close to 147 million kilometres and aphelion distance close to 152 million kilometres.

Earth elliptical orbit Perihelion and Aphelion  Credit: ABAA

Earth reaches perihelion on January 5^th and aphelion on July 4^th. During Perihelion the Sun is in the constellation of Sagittarius and earth will be moving around the Sun at a velocity of 1,08,900km/h and has an angular diameter of 32m32s of arc. During Aphelion on July 4^th Sun will be in the constellation of Gemini and earth will be moving around the Sun at a velocity of 1,07,208km/h and will have angular diameter of 31m28s of arc.

Sun Angular size at Aphelion and Perihelion  Credit: ABAA

Happy Observing and Clear Skies.

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Earth at Perihelion:

Earth will be at Perihelion on 4^th of January; this is the closest distance from earth to Sun. At perihelion the distance between earth and sun is close to 147.09 million km. Since Earth’s orbit eccentricity is very low at 0.016 which is very close to circle the distance between perihelion and aphelion (furthest point from Sun) does not differ much. The Aphelion distance of earth and Sun is 152.10 million km, making the difference just 5.01 million kilometres. This is not much to cause any problem to us, but due to proximity to sun earth receives 7% more sunlight.

The angular size of the Sun seen from earth does not differ much during perihelion and aphelion due to low eccentricity for earth’s orbit. The sun subtends an angle of 0.54183 degrees during perihelion, and at aphelion (furthest distance from sun) the angle subtended is 0.52398 degrees the difference is very small at 0.01785 degrees.

When compared with Mercury which has highest eccentricity of 0.2056 the difference in angular size is apparent during perihelion and aphelion.

 

		Sun			Sun
		Max.Angular Dia			Min.Angular Dia
		Perihelion			Aphelion
Earth		0.54183			0.52398
Mercury		1.7324			1.1414

 

Say Hi to Sun when you go out on January 4^th!

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Sun closest to Earth on January 5th

On January 5^th the earth will be closest to the Sun. During its orbit around the Sun, the earth does not follow a circular path, it deviates a little with an eccentricity 0.0167. This deviation is very small making the distance of earth-sun during the perihelion and aphelion very small. The difference will be close to 3 percent. Perihelion is when a celestial body is closest to the Sun and Aphelion is when the celestial body is farthest from Sun.

On January 5^th earth will be at a perihelion distance of 147 million (Km) and at this distance the Sun's angular diameter will be 32.5 minutes of arc. The orbital velocity of earth during the perihelion will be close to 109044 km/hr.

We can compare this with Aphelion distance of earth, the maximum distance 152 million (Km). The angular diameter at this maximum distance will be 31.45 minutes of arc. The orbital velocity at this distance will be 105444 km/hr.

Earth will be at Aphelion on 5^th July this year.

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