Bad Astronomy. Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax'

Another common idea is that the Sun looks yellow because we are comparing it to the blue sky. Studies have shown that we perceive color not just because of the intrinsic properties of the light but also by comparing that color to some other color we see at the same time. In other words, a yellow light may look even yellower if seen against a background of blue. However, if this is why we see the Sun as yellow, clouds would look yellow, too, so this can’t be right either.

There is another possibility. When the Sun is up high, you can never look directly at it. It’s too bright. Your eyes automatically flinch and water up, making it hard to see straight. You can only see the Sun from the corner of your eye. Under those conditions it’s not surprising that the colors may get a little distorted.

As was mentioned before, at sunrise and sunset the Sun can look remarkably red, orange, or yellow, depending on the amount of junk in the air. Also, the light is heavily filtered by the air, making the Sun look dim enough to be bearable to look at. So the only time of day we can clearly see the Sun is when it’s low in the sky, which, not so coincidentally, is also when it looks yellowish or red. This may also play a part in the perceived color of the Sun. Since it looks yellowish at the only time we can really see it, we remember it that way. This is an interesting claim, although I have my doubts. I remember it most when the Sun is a glowing magenta or red ember on the horizon, and not yellow, so why don’t I think the Sun is red?

I have heard some people claim the Sun does look white to them, but I wonder if they know that sunlight is supposed to be white, and have fooled themselves into thinking it is white to them. It still looks yellow to me, and I know better.

Clearly, there’s more to the Sun than meets the eye.

So, after all this, I’ll ask one more trick question: of all the colors of the rainbow, which color does the Sun produce the most? We know it produces less violet than blue; literally, fewer violet photons come from the Sun than blue. But which color is strongest?

The answer is: green. Surprise! So why doesn’t the Sun look green? Because it isn’t producing only green but a whole spectrum of colors. It just produces more green than any other color. When they are all combined, our eye still perceives the light as white.

Or yellow. Take your pick.

Okay, I lied a minute ago; I still have one more question. If the sky isn’t blue because it reflects the color of the oceans, why are the oceans blue? Do they reflect the sky’s color? No. Of course, they do reflect it a little; they look more steely on overcast days and bluer on sunny days. But the real reason is a bit subtler. It turns out that water can absorb red light very efficiently. When you shine a white light through deep water, all the red light gets sucked out by the water, letting only the bluer light through. When sunlight goes into water, some of it goes deep into the water and some of it reflects back to our eyes. That reflected light has the red absorbed out of it, making it look blue. So the sky is blue because it scatters blue light from the Sun, and the oceans look blue because that’s the only light they let pass through.

At the start of this section, I promised you’d understand all this well enough to explain it to a five-year-old. If a little kid ever asks you just why the sky is blue, you look him or her right in the eye and say, “It’s because of quantum effects involving Rayleigh scattering combined with a lack of violet photon receptors in our retinae.”

Okay, that might not work. In reality, explain to them that the light coming from the Sun is like stuff falling from a tree. Lighter things like leaves get blown all around and fall everywhere, while heavier things like nuts fall straight down without getting scattered around. Blue light is like the leaves and gets spread out all over the sky. Red light is like the heavier material, falling straight down from the Sun to our eyes.

Even if they still don’t get it, that’s okay. Tell them that once upon a time, not too long ago, nobody knew why the sky was blue. Some folks were brave enough to admit they didn’t understand and went on to figure it out for themselves.

Never stop asking why! Great discoveries about the simplest things are often made that way.

5. A Dash of Seasons: Why Summer Turns to Fall

Some examples of bad astronomy are pernicious. They sound reasonable, and they even agree with some other preconceived notions and half-remembered high school science lessons. These ideas can really take root in your head and be very difficult to get out.

Perhaps the most tenacious of these is the reason why we have seasons.

Seasons are probably the most obvious astronomical influence on our lives. Over most of the planet it’s substantially hotter in the summer than in the winter. Clearly, the most obvious explanation is our distance from the Sun. It’s common sense that the closer you are to a heat source, the more heat you feel. It’s also common sense that the Sun is the big daddy of all heat sources. Walking from underneath the shadow of a shade tree on a summer’s day is all you need do to be convinced of that. It makes perfect sense that if somehow the Earth were to get closer to the Sun, it could heat up quite a bit, and if it were farther away our temperatures would dip. And hey, didn’t you learn in your high school science class that the Earth orbits the Sun in an ellipse? So sometimes the Earth really is closer to the Sun, and sometimes it’s farther away. This logic process seems to point inevitably to the cause of the seasons being the ellipticity of the Earth’s orbit.

Unfortunately, that logic process is missing a few key steps.

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).

Clearly, something else must be going on to cause such a huge temperature variation. That something else is the tilt of the Earth’s axis.

Imagine the Earth orbiting the Sun. It orbits in an ellipse, and that ellipse defines a plane. In other words, the Earth doesn’t bob up and down as it orbits the Sun; it stays in a nice, flat orbit. Astronomers call this plane the ecliptic. As the Earth revolves around the Sun, it also spins on its axis like a top, rotating once each day. Your first impression might be to think of the Earth’s axis pointing straight up and down relative to the ecliptic, but it doesn’t. It’s actually tilted by 23.5 degrees from vertical. Have you ever wondered why globe-makers