I want to know how the position of the Earth relative to the sun determines when it's fall or spring if on both equinoxes the incidence of light is the same. What makes these two seasons different from each other?
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$\begingroup$ The difference is in where the Sun is heading. Spring is when the Sun appears to move from South of the equitorial plane to North of the equtorial plane, although the instant of the equinox is when it's on the equitorial plane. $\endgroup$– Greg MillerCommented Sep 2 at 23:37
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4$\begingroup$ Also, the equinox is in Sept rather than Oct, and that is the fall equinox for the Northern hemisphere. $\endgroup$– Greg MillerCommented Sep 2 at 23:38
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5$\begingroup$ I recommend you change the title as it is very confusing! $\endgroup$– deep64blueCommented Sep 3 at 8:09
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2$\begingroup$ "What makes these two seasons different from each other?" If you're asking why the weather distribution around late March is different to late September, that's a very different question than just astronomy. (The temperature, humidity, pressure etc. on the entire Earth does not change that quickly, and local weather is affected by what happens on Earth during preceding months, and the effect is very complex and very dependent on location and geography.) Maybe rephrase your question to be clear what you're asking. $\endgroup$– JiKCommented Sep 3 at 11:59
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$\begingroup$ Our planet has thermal inertia. The solar energy accumulated in previous days and weeks does not dissipate in a moment. Before and after sping equinox incoming solar energy continues to increase (in Northern hemisphere, the opposite for Southern). And for autumn equinox it's reversed. The same reason is why usually July is the hottest month for Northern hemisphere, not June, although solar energy peaks in June 22 - Earth accumulates solar energy from June and needs significant time to dissipate it, and incoming energy in July is just slightly less than in June, so temperature continues to rise $\endgroup$– HeoppsCommented Sep 4 at 12:23
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To put it in simple terms: at the equinox, the Earth's axis is halfway in its apparent movement from pointing away from the Sun (northern winter solstice) to pointing towards the Sun (northern summer solstice).
At each equinox, the Earth's axis is exactly at right angles to where the Sun is, which means the Sun rises due east and sets due west, and day and night are of equal length.
The difference between the two is that after the Spring (or Vernal) Equinox – in late March for the northern hemisphere – the days are longer than the nights, while after the Autumnal Equinox – in late September – the nights are longer than the days.
answered Sep 2 at 23:55