Expert: Tom Whiting - 4/6/2008

Question
Can you explain the quote below? It seems to relate that the  orbit of the earth is below a plane with the sun. Is that true?

Two Equators

From pages 65 and 66 of the 1923 novel, The Boy Adventures in the Land of El Dorado

By A. Hyatt Verrill



The boys slept well, for they had become quite accustomed to nights in the jungle on their trip through Darien, and at dawn they were aroused by the captain's lusty shout of: "Fireside!"

"Whew, but it's cold!" cried Harry as he jumped out of his hammock. "This is chillier than Panama and yet it's almost down to the equator."

Dr. Woodward laughed. "Yes it's pretty cool," he replied, "but it's always cool in the tropical bush at night and early morning and while Guiana is nearer the geographical equator than Panama, you must remember that the thermal equator is closer to Panama than Guiana—runs through the Isthmus, in fact."

"What's that again?" exclaimed Fred. "I never knew there were two equators."

"Yes," his uncle assured him. "The geographical equator is exactly half way between the two poles, but, as a matter of fact,—owing to the position of the earth's axis in relation to the sun,—the true equator, that is the line about the globe which is most directly under the sun and consequently the line of greatest heat or thermal equator, is considerably north of the imaginary equator."

"Well, that's all news to me," declared Fred.

"Same here," chimed in Harry. "Seems to me there's an awful lot they don't teach in school."

Captain Boters, who had been listening attentively with his head cocked on one side, nodded sagely and grinned. "Wha la!" he exclaimed. "I's arrivin' to de consid'ation a man ain't ever too old for to learn somethin' good or bad."

"Right you are, captain!" laughed Dr. Wood¬ward. "I expect I'll learn a lot from you and the Indians before this trip's over. I've already been taught many things from these boys, and one of the most important is that one should never scoff at stories just because they seem improbable."  

Answer
Hi Doug,
the question has not much to do with astronomy, more to do with
weather.  Since it's a fictional book, the writer is snubbing
his nose at people who don't know the real story...the northern hemisphere receives no more direct rays than the southern hemisphere,
and Guiana is probably cooler at night because it's inland and
part of a large continent, whereas Panama's climate is more
moderate being surrounded by water, which is also true of the
entire southern hemisphere, by the way.  (As it's more a water
hemisphere as compared to the northern hemisphere).

What he calls the "thermal equator" isn't a real line on the
earth, but what the writer is doing is taking advantage of the
ITCZ, Inter-Tropical Convergence Zone, also called the Equatorial
(or thermal) Equator as slang....See
http://en.wikipedia.org/wiki/Intertropical_Convergence_Zone
which is more aligned with Panama than Guiana....see Map of ITCZ.

But it's all related to global wind patterns on a large scale,
and not the tilt of the Earth's axis or relationship of the
sun vs. the Earth...that's all "double talk" as the author
snubs his nose at you for lack of your knowledge.

Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

FOLLOW UP:
Oh, and BTW Guiana is not that much farther south than Panama...
if you look at a map, Guiana is from 4-5 N. Latitute, and Panama
is from 6-8 N. Latitude, so 2 degrees of Latitude isn't that much
difference.  (What's the difference in climate between Buffalo
at 42 N and Pittsburgh at 40 N?  Not much. Also, I notice the
Guiana is more mountainous and higher elevation too.
Panama is surrounded on 2 sides by ocean water, that's why it's
climate is more moderate than Guiana, unless your right on, or near, the shoreline. So it's weather or climate related, not astronomical.
Clear skies,
Tom

FOLLOW UP:
Oh, and as far as "planes", one point, the sun, does not form a plane
as it takes two points.  The plane of the Solar System, the ecliptic,
is defined as the center of the sun and the center of the Earth.
Our axial tilt never changes, except for precession over the centuries, but the tilt remains at 23.5 degrees, so there is no
way the sun can spend more time north of the equator than south
of the equator, the two are equal. So no, it is not true.
Clear Skies,
Tom