Friday 5 February 2016

49) “If Earth were a spinning ball heated by a Sun 93 million miles away, it would be impossible to have simultaneously sweltering summers in Africa while just a few thousand miles away bone-chilling frozen Arctic/Antarctic winters experiencing little to no heat from the Sun whatsoever. If the heat from the Sun traveled 93,000,000 miles to the Sahara desert, it is absurd to assert that another 4,000 miles (0.00004%) further to Antarctica would completely negate such sweltering heat resulting in such drastic differences.”

 Oh this is a lovely one! Mr Dubay proves  something false by unimpeachable reasoning. If the earth is 93 million miles from the sun, how could an extra 4000 miles make so much difference to the heat it delivers to the North and South hemispheres in winter and summer?

The answer is simple; it doesn’t, and no scientist has ever claimed that it does. Mr Dubay doesn’t understand at all why winter is colder than summer. And Mr Dubay, I’ll challenge you to find a single science textbook or professional online source that states that the distance has anything to do with it. There are none.

OK, so we have seasons because the globe is tilted relative to the sun by 23.5 degrees. In the northern summer, that tilts the northern hemisphere towards the sun. Sixth months latter, the orbiting earth is on the other side of the sun, so the southern hemisphere is tilted towards the sun.

However, it isn’t the tiny difference in distance that changes the temperature. It is the angle at which the sun’s rays come down on the earth’s surface. 

First, the earth is tilted by 23.4 degrees, so in the northern summer, the north is the part tilted towards the sun for longer, while more of the southern hemisphere is tilted away. You can easily see that the part tilted towards the sun is warmed more than that tilted away . Nothing to do with the distance, though.

Not only is the part tilted towards the sun getting sun for longer in the day, but the sunlight comes down at a sharper angle, and so passes through a smaller thickness of atmosphere. In winter, the sun is at a lower angle , so the sunlight passes through more atmosphere before it reaches the ground level.

For more about this, see this video by Khan Academy:

How the angle of the sun changes the amount of energy that the surface absorbs.

You’ll see why Mr Dubay’s “proof” is nonsense.

In summer, the sun’s rays fall in a concentrated area. In winter, they come in at a low angle, and they are spread over a wider area.

If you don’t get this, or want to see the principle for yourself, here is an experiment you can try:

In a darkened room, shine a, flashlight (torch) or any a well- focused beam of light onto a wall, more or less straight on, are at a shallow angle. You should get a fairly clear circle of light.

Now shine it at the same spot from a shallow angle, well off to one side, but from the same distance.

You will see a stretched-out oval rather than a circle, and the lighted area will look a bit less bright. The same amount of light rays are being spread out over a larger area, so the brightness at any one spot is reduced.

And it’s the same with the heat of the sun’s rays.

So once again, Mr Dubay didn’t even understand the argument he was trying to disprove!

--- I’ve posted a lot of replies to Mr Dubay now, but no flat earther has come back. It’s almost as if they don’t really want a reasoned debate ;-) Surely that can’t be true?

“Nobody says that different temperatures on earth are due to different distances to the sun. These differences are indeed negligible. Conducting a simple experiment will show you how it works:

If you hold your hand perpendicular to a bonfire, it will get warm. Now, keeping your hand at the same distance, tilt it by say, 64° (same angular displacement between Johannesburg and the South Pole). 

You will feel that your hand gets much less warm. That should tell you that thermal radiation on a certain area is dependent on the angle of impact, which in fact is the main reason for different temperatures on different latitudes on earth.

By the way, even Johannesburg is never exposed at 90° and the exposure of either pole is always below 23.5° and 0° for about half a year. That's why it's so cold up and down there.”

1 comment:

  1. Big fan of your blog, but I think that you've got it wrong citing the tilt of the earth and sunlights travel through the atmosphere as the significant factors. It is about the angle that the sun hits the earth, but that's to do with it being a sphere. The tilt creates seasons, but that is a different question altogether.


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