The Sun is a 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium – at the center of our solar system. It’s about 93 million miles (150 million kilometers) from Earth and it’s our solar system’s only star. Without the Sun’s energy, life as we know it could not exist on our home planet. From our vantage point on Earth, the Sun may appear like an ...
Back pain is a common medical problem. Many factors may cause different types of back pain. Learn the parts of the back & what may be causing your back pain.
Back pain is one of the most common medical problems in the United States. Changes to any part of your back—such as ones that may occur with aging, getting hurt, or having other medical conditions—can lead to back pain. It can start suddenly or come on slowly. It may feel like a dull, constant ache, or a sudden, sharp pain.
The Sun is the star at the heart of our solar system. Its gravity holds the solar system together, keeping everything – from the biggest planets to the smallest bits of debris – in its orbit.
The planetary system we call home is located in an outer spiral arm of the Milky Way galaxy. Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids. Beyond our own solar system, there ...