Earth's tilt.

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Earth's tilt.

Postby Dempsey24 » Thu Feb 28, 2019 12:42 pm

I succesfully explained to my son the reasons for the change in seasons (relating to the UK being more face-on, to the sun, in summer than in winter. However, I was glad I was not asked why the earth is tilted, off-axis, in the first place. Please can someone assist. Thankyou.
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Re: Earth's tilt.

Postby Gfamily2 » Thu Feb 28, 2019 1:39 pm

Dempsey24 wrote:I succesfully explained to my son the reasons for the change in seasons (relating to the UK being more face-on, to the sun, in summer than in winter. However, I was glad I was not asked why the earth is tilted, off-axis, in the first place. Please can someone assist. Thankyou.

Good question.
I think the explanation is that all the planets were created from the collision and aggregation of a myriad of smaller bodies, some quite small and some larger. These would have arrived from different directions and would have hit various places on the proto-Earth as it formed.

Overall though, it would be unlikely that the final result of these random collisions would be that the Earth's final rotation axis would be exactly at right angles to the plane of its orbit around the Sun.

All the planets are inclined to a lesser or greater degree - though it may be significant that the two planets closest to the Sun have the smallest inclinations.
Planet- axial inclination in degrees
Mercury ~0.01
Venus 2.3 (but its rotation is retrograde, so you may see it written as 177.4 )
Earth 23.4
Mars 25.2
Jupiter 3.1
Saturn 26.7
Uranus 97.8
Neptune 28.3

Due to the interaction between the planets' shape and the Sun's gravity, it is calculated that axial tilts may vary dramatically over astronomical timescales - however, planet Earth seems to be insulated from this because the anomalous size of our Moon acts as a stabilising factor.
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