A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun.
Sun's diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.
太阳的直径大约是地球的 109 倍，它的质量是地球的 330,000 倍，占据了太阳系总质量的 99.86%。太阳大约四分之三的质量是由氢组成；余下的部分大都是氦；还有少量的重元素，包括氧，碳，氖，铁等。