Space Lessons For Kids
Our home, the planet Earth, may seem pretty big, but it is just one planet of many others that make up the universe. The universe includes stars, meteorites, asteroids, and much more. Although scientists have learned a lot about space beyond Earth, there are still many things that remain a mystery. How big is the universe? Is there life on other planets? These are just some of the unanswered questions about space. As our technology becomes more advanced, we are finding more and more of these answers.
The Solar System
A solar system consists of a star in the center, with other planets or objects revolving around it because of its gravitational force. Just like an object dropped falls to the ground because of gravity, the planets are drawn to the sun: In fact, they're always falling toward the sun, but since they're also moving sideways, they fall sideways and don't get closer to the sun. Our solar system is one of many. It consists of the sun (a star) and eight major planets that revolve around it. It is part of a galaxy, a group of millions of stars that are also held together by gravity. Our galaxy, the Milky Way, consists of more than 100 billion stars! Some of those stars are centers of solar systems of their own and have planets or asteroids surrounding them.
Stars look like faraway specks of light when we look up at the night sky. Close up, however, they are massive balls of bright, fiery gasses, mostly hydrogen and helium. Our sun is the closest star to Earth. There are several types of stars. Some are small and emit blue light; they have cooler temperatures and longer life spans that can last billions of years. Others are hotter and larger and have shorter life spans lasting only a few million years. Cooler stars last longer because they don't use up all of their fuel as quickly. Stars start out as nebulae, or clouds of gas and dust, and nuclear reactions from the gases are what produce the energy and light that appears as a sparkle. Stars will end either as white dwarves, neutron stars, or black holes, depending on their mass and heat.
Groups of stars that are seen together in the night sky are referred to as constellations. You may have heard of the Little Dipper, Big Dipper, or Orion's Belt. These are all famous constellations that can be seen up above in different parts of the sky depending on Earth's position.
Comets look like snowballs flying through the sky. They are collections of particles that release gas and dust as they shoot by. Some comets can be seen on a regular basis in the inner solar system, within our view. Others exist beyond our solar system in an area past Pluto's orbit called the Oort Cloud. Comets are thought to be left over from the Big Bang, when the universe was created.
Comets contain a nucleus, which is made of rock, ice, dust, and other frozen or hard particles, and a coma, which is the stuff surrounding the nucleus. The coma contains gases that are warming and being emitted from the comet as it gets closer to the sun. Many comets, but not all, also have a tail.
Our solar system has eight major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Planets are bodies in space, either rocky or gaseous, that orbit a sun and also have their own gravitational pull. Although there are only a handful of planets in our solar system, scientists believe there are more than 50 sextillion planets in the universe: That's 50 billion trillion planets! About 100 billion of those are believed to be similar to Earth.
Apart from the eight main planets in our system, there are also many dwarf planets. Dwarf planets also revolve around the sun, but they are smaller and don't meet the full definition of a planet. Pluto, once classified as a planet, is now considered a dwarf planet.
The sun is the center of our solar system. It is what makes life for us possible on Earth. Because of its heat, the gases and elements present on Earth could combine to create life billions of years ago. The sun is responsible for day and night, hot and cold, and the seasons, which all depend on where we are on Earth and what part of Earth is facing the sun.
Although the sun is not the largest known star, it is quite a bit bigger than average stars found in the universe. It is about 110 times wider than Earth, and more than a million Earths could fit inside it. It is mostly made up of the gasses hydrogen and helium, and continuous nuclear fusion reactions keep the sun shining bright and providing heat and light to Earth. The sun has used up roughly half of its energy since its birth, and it should continue burning for the next 5 billion years.
The moon orbits Earth. It is about 239,000 miles away from Earth at any given moment. It is made up of a core, mantle, and crust. Only one side of the moon, called the "near side," ever faces Earth. The other side, called the "far side" or "dark side," does not face Earth.
The moon affects the Earth in several ways. Its gravitational pull causes tides in the ocean. Its reflection of light from the sun allows Earth to receive some light even at night. Scientists differ in their views on how the moon was formed. Some believe it formed separately from Earth, and others think it is the result of a collision between Earth and another small planet many millions of years ago.
Meteors, similar to comets, appear as flashes of light in the sky. Also referred to as shooting stars, they result from debris in space coming into Earth's atmosphere and burning up in the process. The debris is often leftover pieces from a comet, asteroid, or other celestial body. If the chunk of debris successfully passes through the atmosphere and lands on Earth, what's left is called a meteorite. Thousands of meteorites make it to Earth's surface each year, although we don't find a lot of them because they land in places like bodies of water or forests.
A galaxy is a group of stars and other matter held together by gravity. Our solar system is part of a galaxy called the Milky Way, which contains billions of stars. Our home in the Milky Way is inside one of its spiral arms.
Galaxies can take on four different shapes: spiral, like the Milky Way; elliptical, or in an oval shape; lenticular, or disc-shaped; and irregular, not like any of the other shapes. Galaxies are thought to have a black hole in their center.