What is the solar system?
It is our sun and everything that travels around it. Our solar system is elliptical in shape. That means it is shaped like an egg. The Sun is in the center of the solar system. Our solar system is always in motion. Nine known planets and their moons, along with comets, asteroids, and other space objects orbit the Sun. The Sun is the biggest object in our solar system. It contains more than 99% of the solar systems mass. Astronomers think the solar system is more than 4 billion years old.
The sun is the star at the center of the solar system. It formed about 5 billion years ago from a huge cloud of gas and dust. About 109 Earths would fit across the face of the sun! One large sunspot could hold several Earths. The suns diameter is 864 thousand miles.
Most of the mass in the solar system is in the sun (99%). The sun spins on its axis from left to right. It takes about 26 days for the sun to spin one time. The suns outer atmosphere is called the corona. Its inner atmosphere is called the chromosphere. Below the photosphere are the convective zone, the radiative zone, and the core. The suns core converts 700 million tons of hydrogen gas into 695 million tons of helium gas every second. The remaining 5 million tons of matter is converted to pure energy. That 5 million tons is about 600 times the amount of water flowing over Niagara Falls in one second. The temperature at the suns core is 15 million degrees (K). Although sunspots are very hot, they are slightly cooler than the rest of the photosphere so they look darker. Sunspots have a dark center called the Umbra and a lighter ring around the outside called the Penumbra. It takes 50 million years for the energy formed deep inside the sun to reach Earth. Earth only gets one-billionth of the total energy produced by the sun. Light, traveling at 186 thousand miles per second, takes just over 8 minutes to reach Earth from the sun. Apollo was both the Greek and Roman god of the sun. He brought life-giving heat and light to Earth and was the patron god of musicians and poets.
Mercury is the closest planet to the sun. Its average distance from the sun is 36 million miles.
Mercury is about 3, 030 miles (4, 878 km) across. That makes it the second-smallest planet in the solar system; only Pluto is smaller. In fact, Mercury is just a little bigger than Earths moon. Its also covered with craters just like the moon. Mercurys year (the time it takes to orbit the sun one time) is 88 Earth days long, but one day (the time it takes to rotate from sunrise to sunrise) is 176 Earth days long. Because Mercury is so close to the sun, it has the smallest orbit of all the planets.
That means it goes around the sun very quickly (88 Earth days or about 3 Earth months). Although Mercury goes around the sun quickly, it spins very slowly on its axis. For every year on Mercury, the planet spins 1 1/2 times (about 59 Earth Days or 2 Earth months). But while Mercury is slowly spinning, it is ...
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