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I've always been told that the equator is the region on Earth that receives the most sunlight.

But I wondered, since the ecliptic is the circular path that the Sun appears to follow over the course of a year, then wouldn't the ecliptic path receive more sunlight than the equator?

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  • $\begingroup$ ryan, are you thinking that because of the ecliptic path, the Tropics of Cancer/Capricorn should have as much or more sunlight than the Equator.... or are you saying that despite the Equator getting more sunlight, the ecliptic (or other factors) would somehow otherwise cause the Tropics of Cancer/Capricorn to overcome the light? $\endgroup$ – JeopardyTempest Mar 21 '18 at 5:52
  • $\begingroup$ Sorry, I didn't make the question clear. It is ecliptic path versus equator, i mean. $\endgroup$ – ryan Mar 21 '18 at 6:33
  • $\begingroup$ sorry I don't understand what you mean by that :-( We'll figure it out if we stick with it :-D Are you saying more sunlight hits the Tropic of Cancer than the Equator... or the same amount... or more sunlight hits the Equator than the Tropic of Cancer? $\endgroup$ – JeopardyTempest Mar 21 '18 at 7:12
  • $\begingroup$ I mean the ecliptic path, where is not the tropic of Cancer nor the tropic of Capricorn. If I'm not wrong, ecliptic path is another circle that only intersect with Cancer circle at one point. $\endgroup$ – ryan Mar 21 '18 at 8:03
  • $\begingroup$ @ryan I did some editing of the question to make it more clear. Please let me know if I kept the intended meaning of it. Otherwise, feel free to roll it back to an earlier revision. $\endgroup$ – Camilo Rada Mar 21 '18 at 20:53
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The ecliptic path, is a well defined trajectory when displayed on the background of the fix stars like in the following figure

enter image description here

(taken from physics.csbsju.edu)

However, there is not such thing as an ecliptic path on the surface of the Earth. If you thought of it as the "Ground track" of a satellite but applied for the Sun, you have to consider that the rotation of the Earth would make that "ground track" of the Sun look very different than the one on the figure above. It would be a spiral going around the Earth ~365 times at latitudes between the tropics of Cancer and Capricorn (remember that the Sun takes a full year to go trough the ecliptic path).

When the the Sun is at its Northernmost declination (the top point of the red curve above), which is ~23° all the points on Earth at latitude ~23° North (the tropic of Cancer) will receive the maximum possible solar irradiation at the solar noon of that day. Once the Sun moves down to declination 22°, it will be the turn of the points at 22° North and so on.

The reason because the Equator is the line that receive more solar radiation is because it is the one that is in average closer to the Sun's ground track (in other words, is the place with the maximum mean solar elevation).

An equivalent visualisation would be to take the mean of the ecliptic, and by looking at the above red line is quite straightforward to see that it would be a flat line on the celestial equator, that translates to the Earth's equator.

Does that makes sense to you?

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  • $\begingroup$ Made perfect sense, I have ignored the effect of rotation. Thx. $\endgroup$ – ryan Mar 22 '18 at 1:46
  • $\begingroup$ @ryan Great! Glad to hear that. Cheers $\endgroup$ – Camilo Rada Mar 22 '18 at 3:49

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