Top 10 Questions Kids Frequently Ask About Earth and How to Answer Them Scientifically

Tell your child: Earth takes 23 hours, 56 minutes, and 4 seconds to complete one full rotation on its axis – astronomers refer to this as an "astronomical day." This doesn't mean our days are 4 minutes shorter. The extra time is gradually accumulated each day, month, and year – where day turns to night and night turns to day.

What you should know: Earth orbits around the Sun. Every day, the Sun moves about 1 degree against the stars in the sky, roughly the size of the Moon's disk. So, with the Sun's movement added, Earth's rotation around the Sun looks much like its rotation on its axis, taking a total of 24 hours. Even though Earth's axial rotation lasts 23 hours, 56 minutes, and 4 seconds, the extra 4 minutes add up daily. This concept might be tricky for adults, but by simplifying it for your child, they will grasp the idea much more clearly.

Tell your child: This is Earth's unique self-rotation. Our planet rotates from west to east. It’s surprising, right? Because we typically think the Sun rises in the east and sets in the west. If you observe from the North Pole, both Earth's and the Moon's movements appear to rotate counterclockwise on their axes.

What you should know: There are two key motions of Earth to consider: its self-rotation on its axis and its orbit around the Sun. From the North Pole, both Earth's and the Moon's rotation on their axes is counterclockwise. Earth’s axis is tilted at about 2 degrees compared to a line perpendicular to the Earth-Sun plane. The plane of the Earth-Moon system is tilted by about 5 degrees compared to the Earth-Sun plane. It takes Earth about 24 hours to complete one full rotation relative to the Sun. However, this rotation is gradually slowing down. This explains why days in the past were shorter than those in the future. Measurements show that today, a day on Earth is about 1.7 milliseconds longer than it was a century ago. Since your child is learning basic concepts, using simple language will make it much easier for them to understand.

Tell your child: Earth's orbit is not fixed; it changes over time, following a perfect cycle. Our planet revolves around the Sun from west to east in an orbit that is nearly circular but elliptical in nature. Right now, Earth is in a nearly perfect circular orbit around the Sun, but soon, it will transition back into an elliptical shape.

What you should know: Earth revolves around the Sun from west to east in an elliptical orbit that's nearly circular. Scientists calculate that it takes Earth about 365.2564 days (365 days and 6 hours) to complete one orbit. This is rounded to 365 days per year, with the extra time accumulating and being added to leap years, which are 366 days long and occur every four years. While orbiting the Sun, Earth maintains a tilt of 66°33′, which does not change as it moves along its orbital plane. A good way to explain this to children is to use specific examples, which can help them understand this concept and apply it when thinking about other planets.

Tell the child: The distance from the Earth's surface to the center is nearly 5,955 km. The majority of the Earth's composition is liquid. The solid crust is only about 66 km thick—thinner than the skin of an apple when scaled proportionally.

What you should know: The Earth's radius is a unit of measurement for its length. Due to the Earth's surface being uneven and not a perfect sphere, its radius is not a standard value. The distance from various points on the Earth's surface to the center ranges from 6,353 km to 6,384 km. There are several ways to model the Earth as a sphere, in which case the average radius is 6,371 km. In contrast, the term 'radius' is only used for perfect spherical objects. According to NASA, the radius at the equator is 6,378 km. It's best not to overwhelm the child with excessive details, as it may be hard for them to grasp fully. Instead, offer additional related knowledge to spark their interest.

Tell your child: The Earth's internal structure is similar to its outer structure, consisting of several layers. The composition of the Earth can be analyzed in two ways: by its chemical properties or by its mechanical properties, such as rheology. From a mechanical perspective, it is divided into five main layers: the lithosphere, asthenosphere, mantle, outer core, and inner core. Chemically, it is divided into the crust, upper mantle, lower mantle, outer core, and inner core.

It's important to know: When analyzing the materials that make up the Earth, you'll find that it consists of 32.1% iron, 30.1% oxygen, 15.1% silicon, and 13.9% magnesium. Most of the iron is concentrated in the Earth's core. In fact, research has shown that the Earth's core is made up of 88% iron, while the Earth's crust contains 47% oxygen. These layers are categorized based on their chemical or rheological characteristics. This is a difficult concept even for adults, but if you explain it to your child in a simplified way, it can help them better understand the issue more clearly.

Tell the child: Scientists believe the theory that the Moon was once part of Earth. This could have been the result of a collision between Earth and a comet or another planet. The impact would have caused a chunk of Earth to break off and drift into space. Over time, this debris formed what is now the Moon. This theory explains why the Moon's geological structure is so similar to Earth's.

What you should know: The giant impact hypothesis suggests that a celestial body the size of Mars, called Theia, collided with early Earth, creating a massive debris ring around it. This debris eventually coalesced to form the Moon. This collision also tilted Earth’s axis by 2°, which leads to our seasons. The oxygen isotope ratios of the Moon closely match those of Earth. These ratios, which can be measured with great precision, are a unique signature for each object in the Solar System. We don’t need to share all the intricate details with the child, as it might be hard for them to grasp. Instead, we can offer additional fun facts to keep them engaged with the topic.

Tell the child: A regular calendar year has 365 days. However, this leaves an extra 6 hours each year, and after four years, these hours add up to a full extra day. As a result, every four years, we have a 366-day year, known as a leap year. The additional day is added to February.

What you should know: In reality, a year on Earth is 365.2564 days long. The remaining 0.2564 days causes the need for a leap year every four years. That’s why every four years, we add an extra day to February, such as in 2004, 2008, 2012, and so on. However, there are exceptions to this rule: years divisible by 100 (like 1900, 2100, etc.) are not leap years unless they are also divisible by 400 (like 1600 and 2000). Space studies can be complex, so simplifying them and adding fun facts can help children better understand these concepts.

Tell your child: The shape of the Earth is a question that has puzzled humans for centuries. Many theories have been proposed over time to explain its shape. Early astronomers believed the Earth was flat. However, we now know that Earth is an oblate spheroid. It's a sphere that is slightly squished at the poles and bulges around the equator. This means the Earth is a little flatter at the North and South Poles due to gravity.

Interesting fact: The Earth is almost spherical, with flattened poles and an expanded equator. This bulging effect is caused by the planet's rotation. The distance between the poles is about 43 km shorter than the diameter at the equator. Although Mount Everest is the highest mountain on Earth, the peak of Mount Chimborazo in Ecuador is actually farther from Earth's center. People have long believed Earth was round, but this idea wasn't widely accepted until the 6th century BC. Today, thanks to modern astronomy and space travel, scientists have confirmed that Earth is an oblate spheroid. However, it's best to simplify these concepts for children, as they might not yet understand such complex information. Using relatable examples can help them grasp the idea and apply it to thinking about other planets.

Tell your child: Earth is home to billions of people, animals, and plants. While it’s not the largest planet in the Solar System, its size is still enough to amaze anyone. In 2013, a man from Japan walked around the world in more than four and a half years. But for us, a group of over 22,400 people ran together, in sync, with the same goal, and finished in less than 38 hours.

Interesting fact: Earth is not a perfect sphere. Its surface has bumps (mountains) and dips (ocean valleys), so its radius isn't the same everywhere. Scientists estimate the distance from Earth’s core to its outer surface to be between 6,353 km and 6,384 km. The average radius of Earth is taken to be 6,371 km, meaning the diameter of Earth is approximately 12,742 km. The imaginary line that runs around Earth’s widest point is called the equator. This line divides Earth into the Northern and Southern Hemispheres. You don't need to overwhelm your child with too many details. Instead, tell them a story about the fascinating facts related to this topic to spark their interest.

Tell your child: About 70% of our planet is covered by water, with the remaining 30% being solid land above sea level. This is why it's called the "continental crust." When astronauts first went to space and saw Earth from afar, they nicknamed it the "Blue Planet" because of the vast oceans.

What you should know: If all the water on Earth, in any form (vapor, ice, or liquid), were collected into a single sphere, that sphere would have a diameter of 1,385 km. That’s nearly 300 km shorter than the distance from Ho Chi Minh City to Hanoi (according to Wikipedia). The total volume of water on Earth is about 1,386 million cubic kilometers. Every day, about 1,170 cubic kilometers of water evaporate into the atmosphere. Around 12,900 cubic kilometers of water always exist as vapor in our atmosphere. If all this water were to fall at once, Earth’s surface would be submerged by about 1 inch (2.5 cm). If all the water on Earth were poured over the United States, it would cover the country by about 145 km. You don’t need to overwhelm your child with too much detail. Instead, focus on interesting facts around the topic to keep them engaged and curious.