Let's start with what a star is. A star is a giant ball of gas. New stars form in large clouds of gas and dust. Hydrogen is by far the most abundant element in most stars. In a star's core, hydrogen nuclei join to make helium. This joining is called nuclear fusion.

Stars come in different sizes. There are bigger stars and smaller stars than the Sun. Our Sun is a medium-sized star. A red dwarf is too faint to see with the unaided eye. Stars also come in different colors, such as red, orange, yellow, white and blue. A star's color tells about its temperature. Blue-white stars are much hotter than the Sun. Red stars are cooler.

Binary stars are two stars that orbit each other. Gravity holds them together. Stars are gathered into huge groups called galaxies. The Sun belongs to a galaxy called the Milky Way. As of November 2026, the Milky Way galaxy contains more than 100 billion stars.

The Sun is the closest star to Earth. Except for the Sun, stars are so far away that they look like pinpoints of light. A light-year is the distance that light travels in one year. Proxima Centauri is the nearest star to the Sun. As of November 2026, it is about 4.24 light-years away.

On a clear night away from streetlights, a person can see a few thousand stars without a telescope. Daytime sunlight hides the stars from view. People long ago grouped stars into patterns called constellations. Stars twinkle because we see their light through Earth's air. Starlight bends a little each time it enters warmer or cooler air. Seen from the Moon, where there is no air, stars do not twinkle at all.

Names in the sky can fool you. Planets twinkle less than stars do. They tend to glow with a steady light. A shooting star is not a star. It is a streak of light from a meteoroid burning up in Earth's atmosphere. Polaris is not the brightest star in the sky. Sirius is the brightest star in the night sky.

Words to know

• hydrogen: lightest gas
• fusion: joining together
• binary: two together
• meteoroid: space rock bit
• constellations: star patterns

The short version

A star is a giant ball of gas. New stars form in large clouds of gas and dust. In a star's core, hydrogen nuclei join to make helium in a process called nuclear fusion. The Sun is the closest star to Earth. As of November 2026, the nearest star to the Sun is Proxima Centauri, about 4.24 light-years away.

Quick facts

• A star is a giant ball of gas.
• New stars form in large clouds of gas and dust.
• In a star's core, hydrogen nuclei join to make helium in nuclear fusion.
• A light-year is the distance that light travels in one year.
• Stars twinkle because we see their light through Earth's air.