Bad Astronomy: Misconceptions and Misuses Revealed, from ...

A DASH OF SEASONS 49
It’s true that the Earth orbits the Sun in an ellipse. We know it
now through careful measurements of the sky, but it isn’t all that
obvious. For thousands of years it was thought that the Sun orbited
the Earth. In the year 1530, the Polish astronomer Nicolaus Copernicus
first published his idea that the Earth orbited the Sun. The
problem is, he thought the Earth (and all the planets) moved in a
perfectly circular path. When he tried to use that idea to predict
the positions of the planets in the sky, things came out wrong. He
had to really fudge his model to make it work, and it never really
did do a good job predicting positions.
In the very early part of the 1600s, Johannes Kepler came
along and figured out that planets move in ellipses, not circles.
Here we are 400 years later, and we still use Kepler’s discoveries to
figure out where the planets are in the sky. We even use his findings
to plan the path of space probes to those planets; imagine
Kepler’s reaction if he knew that! (He’d probably say: “Hey! I’ve
been dead 350 years! What took you so long?”)
But there’s a downside to Kepler’s elliptical orbits; they play
with our common sense and allow us to jump to the wrong conclusions.
We know that planets, including our own, orbit the Sun
in these oval paths, so we know that sometimes we’re closer to the
Sun than at other times. We also know that distance plays a role
in the heat we feel. We therefore come to the logical conclusion
that the seasons are caused by our changing distance from the Sun.
However, we have another tool at our disposal beside common
sense, and that’s mathematics. Astronomers have actually measured
the distance of the Earth to the Sun over the course of the year.
The math needed to convert distance to temperature isn’t all that
hard, and it is commonly assigned as a homework problem to
undergraduate-level astronomy majors. I’ll spare you the details and
simply give you the answer. Surprisingly, the change in distance
over the course of the seasons amounts to only a 4-degree Celsius
(roughly 7 degrees Fahrenheit) change in temperature. This may
not surprise people from tropical locations, where the local temperature
doesn’t vary much over the year, but it may come as a shock
to someone from, say, Maine, where the seasonal temperature
change is more like 44 degrees Celsius (80 or so degrees Fahrenheit).