Stars
A star is any massive self-luminous celestial body of gas that shines by radiation derived from its internal energy sources. Of the tens of billions of trillions of stars in the observable universe, only a very small percentage are visible to the naked eye. Stars are made of very hot gas. This gas is mostly hydrogen and helium, which are the two lightest elements. Stars shine by burning hydrogen into helium in their cores, and later in their lives create heavier elements. Methuselah is believed to be the oldest star in the entire known universe, having formed over 14 billion years ago. Its age makes it older than the universe itself. The stars seem to twinkle in the night sky due to the effects of the Earth's atmosphere. When starlight enters the atmosphere, it is affected by winds in the atmosphere and areas with different temperatures and densities. This causes the light from the star to twinkle when seen from the ground. Stars can be as cool as 2500 Kelvin ...