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Today's Wonder of the Day was inspired by Sonika from stone ridge, VA. Sonika Wonders, " Why are planets spherical and not cuboid or any other shape. " Thanks for WONDERing with us, Sonika!

There are a few basic astronomy facts you probably take for granted. For example, Earth is and Earth travels around the Sun. However, have you ever considered how revolutionary those ideas really are?

Take a walk outside to prove the point. Does it seem like you're walking on a giant, ball? Do you feel yourself flying through the air around the Sun? No! Based upon your senses, would you guess that Earth is ? Does it seem like you're traveling around the Sun instead of the other way around?

Hundreds of years ago, people believed Earth was flat and that the Sun traveled around Earth. We now know different, but were those views really all that crazy back then? Probably not! The evolution of scientific knowledge has proven that, when it comes to astronomy, you can't always rely on your senses.

We already know that Earth is . But why is it ? And is it perfectly like a rubber ball? Let's see what science can tell us about the answers to those questions.

Two features of Earth that determine its are and . These features are, in fact, interrelated . attracts other , resulting in the we call . Smaller objects, such as a car or a house, have tiny gravitational forces. The amount of throughout Earth, however, is huge and really adds up.

Scientists theorize that about 4.6 billion years ago, the solar system was a cloud of dust and gas. As pulled the matter in on itself, it began to spin and clump up, forming the sun, planets, moons, and other space objects. Earth's rocky core was the first part of our planet to form, with dense matter sinking to the center and binding together. Then lighter pieces gathered and formed Earth's crust.

As Earth's added up from all this matter and gravitational forces increased, the matter attempted to take the most efficient possible: a . If Earth was a , its corners would be farther away from its center than other points. Because acts equally on everything, the corners would need to be pulled closer to the center.

The result of evening out the uneven places is that you end up with a in which every point on the is the same distance from the center. The only that fits that definition is the . So, is the answer to why Earth is !

If you've seen pictures of asteroids that exist in outer space, you may have noticed that some of them are irregular, rocky shapes. That's because they're not big enough to pull themselves into a . If they continue to grow and gain , eventually they, too, will form themselves into a . Astronomers have made that ability - the ability to form into a - as one of the requirements to be considered a planet!

If you've seen pictures of Earth from space, Earth does indeed look like a perfectly- ball. Astronauts have even nicknamed it the "Blue Marble." Scientists will tell you, however, that Earth is not perfectly . Its true is closer to that of an .

Earth's constant rotation creates centrifugal forces that make Earth wider at the than the poles. How much wider? About 70,000 feet wider! You've probably also noticed that Earth's isn't flat. High mountain ranges and deep ocean trenches also contribute to Earth's slightly-irregular .

Earth's is also not . It's always changing. Sometimes these changes are regular, such as daily tides that affect the oceans and Earth's crust. Other changes are irregular and extremely slow, such as the movement of Earth's plates. Sometimes natural disasters can result in sudden changes, such as is the case with earthquakes, volcanic eruptions, and meteor strikes.

There's actually a field of science dedicated to measuring and monitoring Earth's size and . It's called , and scientists with the National Geodetic Survey keep an eye on Earth's ever-changing and size.

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Today's Wonder of the Day was inspired by Sonika from stone ridge, VA. Sonika Wonders, " Why are planets spherical and not cuboid or any other shape. " Thanks for WONDERing with us, Sonika! There are a few basic astronomy facts you probably take for granted.

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The word "tides" describes the regular rising and falling of the ocean's surface. Large lakes, such as the Great Lakes, also have tides, but the change in water level is only inches. Ocean tides are measured in feet.

Tides are caused by gravitational forces of the moon and the sun. The sun is huge, but it is 360 times farther from the Earth than the moon.

Even though the moon is much smaller than the sun, it has two times more influence on tides than the sun, simply because it is much closer to the Earth.

The moon's gravitational force pulls on water in the oceans and causes bulges that create "high ." The moon's gravitational pull is strongest on the side that faces the Earth. You might think that the opposite side of the Earth would experience a low , but that would be incorrect!

Amazingly, the moon's gravity creates a high on both sides of the Earth. As the moon's gravity pulls on the Earth, it pulls water into a on the side closest to it.

Meanwhile, on the other side of the Earth, there is another high created by the moon slightly pulling the Earth away from the still water on that side.

There are a few different types of special tides that occur depending on the of the moon. Spring tides are strong tides that occur when the Earth, the moon and the sun are in a line.

During these times, the combined gravitational pull of the moon and the sun is very strong. Spring tides occur during the and phases.

The Proxigean Spring is a rare, very high that occurs when the moon is unusually close to the Earth and in a . During this time, the moon is between the Earth and the sun.

"Neap tides" are weak tides that occur when the gravitational forces of the moon and the sun are perpendicular to one another, pulling on the Earth from different directions. Neap tides occur during the quarter moon .

Tidal facts:

Isaac Newton first explained tides scientifically in 1686.

The highest tides in the world occur in the Bay of Fundy in Nova Scotia, Canada.

Because the moon moves around the Earth, it's not always in the same place at the same time each day. So, the times for high and low tides change by 50 minutes each day.

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The moon has more pull on Earth than you might expect. Dive on in! This wonder is going to turn the tide of your mind.

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What Causes Day and Night? (English) - YouTube

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What Causes Day and Night? (English) - YouTube

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Earth's Rotation & Revolution: Crash Course Kids 8.1 - YouTube

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Earth's Rotation & Revolution: Crash Course Kids 8.1 - YouTube

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Earth's Rotation & Revolution: Crash Course Kids 8.1

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Day and Night Explanation,Causes Science for Kids - YouTube

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Day and Night Explanation,Causes Science for Kids - YouTube

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Day and Night Explanation,Causes  Science for Kids

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Everyone knows that day is the time between sunrise and sunset, when it's light, and night is the rest of the time, when it's dark. But what makes the Sun rise and set? You can take a giant step into space and observe the Sun/Earth/Moon system in action.