Introduction to Stars
Composed primarily of hydrogen and helium, stars are massive, luminous objects whose energy is generated by nuclear fusion within their cores. Stars are fundamental celestial entities that illuminate the cosmos and play a crucial role in the structure and evolution of the universe. The most important star in our lives is the Sun — without it, there would be no life on Earth.
A Close Look at the Sun
The Center of Our Solar System
The Sun is a massive, hot ball of plasma, emitting energy produced by nuclear fusion at its core.
Below are various characteristics of the Sun:
Age
The Sun is roughly 4.6 billion years old — just a little older than the Earth. The Sun is expected to live another ~ 5 billion years before it turns into a White Dwarf — exhausting all of its nuclear fuel.
Size
The Sun is nearly a perfect sphere, with a radius of 696,300 kilometers or 432,700 miles — 109 times that of the Earth. In fact, you can fit 1,300,000 planet Earths within the volume of the Sun.
Distance
The Sun orbits at a distance of 1 Astronomical Unit (AU) from the Earth. This is a distance of 150,000,000 kilometers or 8 light-minutes away. If a message was sent from Earth to the Sun (or vice-versa) it would take 8 minutes for that message to travel.
Fusion
The sun is kept alive by the physical process known as nuclear fusion. The sun has been fusing hydrogen into helium for nearly 5 billion years, and it will continue to do so until it exhausts all the hydrogen in its core — reaching its fate in ~ 7 billion years.