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.
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| 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 5th and aphelion on July 4th. 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 4th 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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