The Inner Planets

 The Inner Planets

    The four inner planets are Mercury, Venus, Earth, and Mars. They are closest to the sun in the solar system. These planets are also called the "rocky planets."
    Mercury is the second-smallest planet. It is the closest one to the sun. Mercury is about the same size as the moon. It is the fastest moving planet.
    Venus is the second planet from the sun. It is the hottest planet in the solar system. Venus looks like Earth. It is about the same size. Venus is called "the morning star" or "the evening star." Venus can easily be seen at dawn or at dusk.
    Earth is the third planet from the sun. It is the fifth-largest planet. It has one moon. Earth is the only known planet on which there is life. Earth rotates on an imaginary, or a pretend, line. This line is called an axis. Earth leans, or tilts, on this axis. The tilting causes different parts of the Earth to face the sun at different times of the day and year. As a result, we have morning, afternoon, and evening in a day as well as four seasons in a year.
    Mars is known as the "red planet." It is the fourth planet in order from the sun and has two moons. It takes 687 days for Mars to orbit the sun. Like Earth, Mars has seasons. Since it takes Mars longer to orbit the sun, its seasons are longer.