Stephanie Spera, University of Richmond

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Why can’t it always be summer? – Amanda, age 5, Chile

With its long days just itching to be spent by water doing nothing, summer really can be an enchanting season. As Jenny Han wrote in the young adult novel “The Summer I Turned Pretty”: “Everything good, everything magical happens between the months of June and August.”

But all good things must come to an end, and summer cannot last forever. There’s both a simple reason and a more complicated one. The simple reason is that it can’t always be summer because the Earth is tilted. The more complicated answer requires some geometry.

I’m a professor of geography and the environment who has studied seasonal changes on the landscape. Here’s what seasons have to do with our planet’s position as it moves through the solar system.

Closeness to the Sun doesn’t explain seasons

First, you need to know that the Earth is a sphere – technically, an oblate spheroid. That means Earth has a round shape a little wider than it is tall.

Every year, Earth travels in its orbit to make one revolution around the Sun. The Earth’s orbit is an ellipse, which is more like an oval than a circle. So there are times when Earth is closer to the Sun and times when it’s farther away.

A lot of people assume this distance is why we have seasons. But these people would be wrong. In the United States, the Earth is 3 million miles closer to the Sun during winter than in the summer.

Spinning like a top

Now picture an imaginary line across Earth, right in the middle, at 0° latitude. This line is called the equator. If you drew it on a globe, the equator would pass through countries including Brazil, Kenya, Indonesia and Ecuador.

Everything north of the equator, including the United States, is considered the Northern Hemisphere, and everything south of the equator is the Southern Hemisphere.

Now think of the Earth’s axis as another imaginary line that runs vertically through the middle of the Earth, going from the North Pole to the South Pole.

As it orbits, or revolves, around the Sun, the Earth also rotates. That means it spins on its axis, like a top. The Earth takes one full year to revolve around the Sun and takes 24 hours, or one day, to do one full rotation on its axis.

This axis is why we have day and night; during the day, we’re facing the Sun, and at night, we’re facing away.

But the Earth’s axis does not go directly up and down. Instead, its axis is always tilted at 23.5 degrees in the exact same direction, toward the North Star.

The Earth’s axis is tilted due to a giant object – perhaps an ancient planet – smashing into it billions of years ago. And it’s this tilt that causes seasons.

It’s all about the tilt

So that means in June, the Northern Hemisphere is tilted toward the Sun. That tilt means more sunlight, more solar energy, longer days – all the things that make summer, well, summer.

At the same time, the Southern Hemisphere is tilted away from the Sun. So countries such as Australia, Chile and Argentina are experiencing winter then.

To say it another way: As the Earth moves around the Sun throughout the year, the parts of the Earth getting the most sunlight are always changing.

Fast-forward to December, and Earth is on the exact opposite side of its orbit as where it was in June. It’s the Southern Hemisphere’s turn to be tilted toward the Sun, which means its summer happens in December, January and February.

If Earth were not tilted at all, there would be no seasons. If it were tilted more than it is, there would be even more extreme seasons and drastic swings in temperature. Summers would be hotter and winters would be colder.

Defining summer

Talk to a meteorologist, climate scientist or author Jenny Han, and they’ll tell you that for those of us in the Northern Hemisphere, summer is June, July and August, the warmest months of the year.

But there’s another way to define summer. Talk to astronomers, and they’ll tell you the first day of summer is the summer solstice – the day of the year with the longest amount of daylight and shortest amount of darkness.

The summer solstice occurs every year sometime between June 20 and June 22. And every day after, until the winter solstice in December, the Northern Hemisphere receives a little less daylight.

Summer officially ends on the autumnal equinox, the fall day when everywhere on Earth has an equal amount of daylight and night. The autumnal equinox happens every year on either September 22 or 23.

But whether you view summer like Jenny Han or like an astronomer, one thing is certain: Either way, summer must come to an end. But the season and the magic it brings with it will be back before you know it.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Stephanie Spera, Assistant Professor of Geography and the Environment, University of Richmond

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Richard L. Lindroth, University of Wisconsin-Madison and Patricia C. Fernandez, Universidad de Buenos Aires

When we walked with a colleague into an aspen forest near Madison, Wisconsin, in the early spring of 2021, we expected to finalize our plans for a research project on several species of insects that live and feed on the trees. Instead, we found a forest laden with fuzzy, brown egg masses.

These masses, belonging to an invasive species known as the spongy moth, brought our plans to a screeching stop. We knew that within weeks, hungry spongy moth caterpillars would strip the forest bare.

We are chemical ecologists interested in how plant chemistry influences the interactions between plants and plant-feeding insects. As seasoned scientists, we’ve seen that good science stories sometimes end up nowhere near where the researchers first anticipated. This is one of those stories. And like many good stories, it incorporates villains, beauty, poison and death.

After an initial period of distressed hand-wringing about the fate of our aspen forest, we pivoted our research plans. We decided to address how defoliation – another word for leaf consumption – by an invasive species might alter the chemical composition of plants, to the detriment of native species.

All plants produce defense compounds to fend off herbivores, like insects, that try to eat them. These defenses include well-known chemicals like tannins, caffeine and cyanide. In turn, insects have evolved adaptations to these chemical defenses tailored to the particular species that they feed on.

The results from this study surprised even us and were published in September 2023 in the journal Ecology and Evolution.

The ecological players

Quaking aspen (Populus tremuloides) is the most widespread tree species in North America.

As a keystone species, aspen provides food and shelter for many forest organisms. Without these trees, forests across much of North America would look very different. Aspen has been ecologically successful in part because of its unique chemistry. It produces a class of defense compounds called salicinoids. Under most conditions, these defenses keep herbivores from fully defoliating the trees.

Invasive spongy moths (Lymantria dispar) are the most destructive defoliators of broadleaf forests in North America. Aspen is a favored food plant of spongy moths, which feed on expanding leaves in early summer. At high population densities, spongy moths can defoliate extensive areas of forest.

This spongy moth-induced carnage does not bode well for other insects that depend on aspen for food, such as the native silk moth Anthereae polyphemus, which feeds on aspen from mid- to late summer.

A natural experiment

From May through June 2021, spongy moth caterpillars ate nearly every green leaf in our aspen forest.

By early July, however, the trees grew another full set of leaves. A second aspen forest of the same age, located 4 miles (6 kilometers) away, experienced no defoliation.

This combination of damaged and undamaged forests provided the perfect conditions for what scientists call a natural experiment. The undamaged forests served as an experimental control that we could compare with the damaged forest to evaluate the consequences of spongy moth defoliation for insects that feed in late summer.

We collected leaves from both forests in late summer and analyzed them for levels of salicinoids.

We also fed the native polyphemus caterpillars leaves from either the defoliated or control forest to see how the defense compounds might influence their ability to live and grow.

We found that after defoliation by spongy moths, aspen trees grew a second set of leaves with much higher levels of salicinoids – an average of 8.4 times higher. In contrast, the control forest had leaves with far lower salicinoid levels, typical of aspen in late summer.

The high levels of defense compounds in the defoliated forest caused serious damage to the native silk moth caterpillars. Few caterpillars survived when fed leaves from the previously defoliated forest. Those that did survive had stunted growth.

Ecological implications

Our research showed for the first time how an invasive species can harm a native species by making their shared food resource far more toxic. And this type of ecological dynamic is likely not restricted to just aspen and silk moth caterpillars.

Over 100 different species of insects and mammals feed on aspen, and our earlier research has shown that high levels of salicinoids are harmful to many of them. Other tree species, like oaks, also produce more defense compounds after spongy moth defoliation, which could affect native herbivores.

Insects are critically important for the functioning and flourishing of all terrestrial ecosystems. But scientists have seen their numbers and diversity decline worldwide, a phenomenon called the insect apocalypse.

The causes of these declines are many, varied and far from completely known. Research like this is helping to fill that gap. Plant toxin-mediated indirect effects of invasive species appear to be yet one more cut in the death by a thousand cuts experienced by insects worldwide.

Finally, our story is one of science in action. Scientists cannot fully anticipate how natural events may disrupt the best-laid research plans, especially for field projects. Floods, droughts, tornadoes, lightning strikes, insect outbreaks – our research groups have experienced them all.

Occasionally, though, researchers can counter these challenges with creative ingenuity and scientific adaptability. And those can lead to surprising breakthroughs in our understanding of this extraordinary world.

Richard L. LindrothUniversity of Wisconsin-Madison and Patricia C. Fernandez, Professor of Agronomy and CONICET Scientist, Universidad de Buenos Aires

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Kimberly Baker, Clemson University

With rising rates of obesity in the U.S. and increasing attention being paid to the health harms of processed foods, it’s clear that far more could be done to help consumers make healthy food choices.

A bill known as the TRUTH in Labeling Act has been sitting before Congress since late 2023. If passed, it would require U.S. food manufacturers to add a second nutrition label to the front of product packages, in addition to the ones currently found on the back or side panel. It would also require the label to highlight any potentially unhealthy ingredients in the product, such as the amount of sugar, sodium and saturated fat it contains.

The proposed legislation would provide consumers with a standardized, easy-to-read and quick way to decide whether a product is a healthy choice. Should the bill, which is still in committee, become law, the front-of-package label would be regulated by the U.S. Food and Drug Administration.

The current nutrition facts label, typically featuring more detailed nutritional information and found on a product’s side panel, would remain unchanged.

As a food safety extension specialist who works with farmers, entrepreneurs, manufacturers and the government to help bring healthy food to shoppers, I believe that consistent front-of-package labeling would greatly benefit consumers by offering a straightforward way to compare multiple products, helping them make more informed choices.

Even if passed, it will take time for the FDA to interpret the law and standardize the design and format. And it might be years before all food manufacturers are required to use the new label. In the meantime, more than 175 million Americans are overweight or obese, and with each passing day, that number grows.

Why the change?

The newly proposed legislation is the latest effort by lawmakers to educate the public about smart food choices. Congress began requiring standardized nutrition labels on food packages through the Nutrition Labeling and Education Act of 1990.

But in the 34 years since that first label appeared, the obesity rate has more than tripled; 40% of Americans are now obese. Another 31% are overweight, and diet-related chronic illnesses, including heart disease, stroke, cancer, hypertension and Type 2 diabetes are rampant. About 60% of U.S. adults – 130 million people – have at least one of these chronic illnesses.

All of these diseases are associated with consuming too much sugar, sodium or saturated fat – three key ingredients the front label will focus on.

Labels help shoppers make better choices

There’s another reason to require a second, easy-to-notice, easy-to-comprehend label. Only about 40% of Americans frequently read the existing nutrition facts label; some shoppers say they don’t understand it. A simpler label with a more direct message might help those consumers. In fact, some studies suggest front-of-package labels do assist shoppers in making smart choices.

Research shows that those who frequently read the current label tend to have healthier diets than those who don’t. For example, frequent readers are almost four times more likely than rare readers to meet the recommended daily fiber intake.

Now the bad news: Even the frequent readers met their fiber goals only about 13% of the time. That isn’t good, but it’s an improvement over the rare readers, who meet their goals a paltry 3.7% of the time.

For the record, the daily recommendation for fiber is 25 grams for women and 38 for men under 50; its slightly less for those over 50.

Some foods still exempt

It’s possible you’ve already seen some front-of-package nutritional labels on food products. But these labels are not regulated by the government. Known as the “facts-up-front” labeling system, it’s strictly voluntary and a choice of the individual food manufacturer, with label designs and formats provided by the Consumer Brands Association, a trade association representing the food industry. Only a small number of manufacturers have chosen to put these labels on their products.

That said, more research is needed to know how long-term behavior may change due to front-of-package labeling. But at least one food safety advocacy organization, while supportive of front-of-package labels, says the trade association’s facts-up-front system is less than optimal.

Even if the TRUTH in Labeling Act passes as currently written, some foods could remain exempt from the nutritional label requirement, including fish, coffee, tea and spices.

There is one caveat, however. If any product makes a nutritional or health claim on its package – including those that are normally exempt – then a nutrition facts label must be on it.

Kimberly Baker, Food Systems and Safety Program Team Director, Clemson University

This article is republished from The Conversation under a Creative Commons license. Read the original article.