Chloe Effron/iStock
Chloe Effron/iStock

Why Are the Days Longer in Summer?

Chloe Effron/iStock
Chloe Effron/iStock

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Did you know that when it’s summer in North America it is winter in some other continents, like South America and Australia? Picture Earth as a round ball with a line drawn around the middle. That line is the equator (ee-QUAY-ter), and it divides our planet into two halves: the Northern Hemisphere (HEM-iss-feer) and the Southern Hemisphere. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. In summer the days are longer, while in winter they are shorter.

On maps and globes, the Earth looks straight up and down, with the North Pole at the top and the South Pole at the bottom. Actually, though, the Earth is tilted 23.4 degrees! (A circle is 360 degrees.) This tilt is the reason that days are longer in the summer and shorter in the winter. The hemisphere that’s tilted closest to the Sun has the longest, brightest days because it gets more direct light from the Sun’s rays. One hemisphere doesn’t stay tilted closer to the Sun all year, however.

Because Earth doesn’t stay in one place! It orbits (or circles) the Sun, making an oval shape. One orbit takes one year. Because the Earth is tilted, one hemisphere will be closest to the Sun for part of the year. But as Earth continues orbiting the Sun, that tilt puts the other hemisphere closer to the Sun. In the Northern Hemisphere, the longest day of the year, called the summer solstice (SOAL-stiss), happens around June 21, because that’s when the North Pole is tilted closest to the Sun. The opposite happens around December 21: the South Pole is closest to the Sun, so the Northern Hemisphere has its shortest day of the year. Meanwhile, the Southern Hemisphere is having its own summer solstice.

Want to see it for yourself? Have an adult help you set up this fun experiment! You can also watch Bill Nye the Science Guy explain the seasons.


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'Lime Disease' Could Give You a Nasty Rash This Summer
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iStock

A cold Corona or virgin margarita is best enjoyed by the pool, but watch where you’re squeezing those limes. As Slate illustrates in a new video, there’s a lesser-known “lime disease,” and it can give you a nasty skin rash if you’re not careful.

When lime juice comes into contact with your skin and is then exposed to UV rays, it can cause a chemical reaction that results in phytophotodermatitis. It looks a little like a poison ivy reaction or sun poisoning, and some of the symptoms include redness, blistering, and inflammation. It’s the same reaction caused by a corrosive sap on the giant hogweed, an invasive weed that’s spreading throughout the U.S.

"Lime disease" may sound random, but it’s a lot more common than you might think. Dermatologist Barry D. Goldman tells Slate he sees cases of the skin condition almost daily in the summer. Some people have even reported receiving second-degree burns as a result of the citric acid from lime juice. According to the Mayo Clinic, the chemical that causes phytophotodermatitis can also be found in wild parsnip, wild dill, wild parsley, buttercups, and other citrus fruits.

To play it safe, keep your limes confined to the great indoors or wash your hands with soap after handling the fruit. You can learn more about phytophotodermatitis by checking out Slate’s video below.

[h/t Slate]

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Why Eating From a Smaller Plate Might Not Be an Effective Dieting Trick 
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iStock

It might be time to rewrite the diet books. Israeli psychologists have cast doubt on the widespread belief that eating from smaller plates helps you control food portions and feel fuller, Scientific American reports.

Past studies have shown that this mind trick, called the Delboeuf illusion, influences the amount of food that people eat. In one 2012 study, participants who were given larger bowls ended up eating more soup overall than those given smaller bowls.

However, researchers from Ben-Gurion University in Negev, Israel, concluded in a study published in the journal Appetite that the effectiveness of the illusion depends on how empty your stomach is. The team of scientists studied two groups of participants: one that ate three hours before the experiment, and another that ate one hour prior. When participants were shown images of pizzas on serving trays of varying sizes, the group that hadn’t eaten in several hours was more accurate in assessing the size of pizzas. In other words, the hungrier they were, the less likely they were to be fooled by the different trays.

However, both groups were equally tricked by the illusion when they were asked to estimate the size of non-food objects, such as black circles inside of white circles and hubcaps within tires. Researchers say this demonstrates that motivational factors, like appetite, affects how we perceive food. The findings also dovetail with the results of an earlier study, which concluded that overweight people are less likely to fall for the illusion than people of a normal weight.

So go ahead and get a large plate every now and then. At the very least, it may save you a second trip to the buffet table.

[h/t Scientific American]

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