The Sun is the closest star to Earth. A star is a giant ball of gas, and new stars form in large clouds of gas and dust. A giant molecular cloud where many stars form is called a stellar nursery. A protostar is a baby star. It is a hot core that forms as a clump in a cloud collapses, before fusion begins. This is how a star's story starts, and we can follow that story from its start to its end.

Let's see what keeps a star shining, and how long it can shine. In a star's core, hydrogen nuclei join to make helium in a process called nuclear fusion. Hydrogen is by far the most abundant element in most of the stars. Fusion releases energy that heats the star and keeps it from collapsing under gravity. A star's mass decides how fast it uses its fuel. Massive stars burn out in millions of years while low-mass stars shine much longer.

The Sun is a medium-sized star, and there are bigger stars and smaller stars than the Sun. Stars come in different colors, such as red, orange, yellow, white and blue. When a star runs out of hydrogen in its core, it swells into a red giant. A dying red giant blows away its outer layers, making an expanding cloud of dust and gas called a planetary nebula. A star like the Sun ends as a white dwarf, a roughly Earth-sized cinder that cools over billions of years.

A white dwarf is about as big as Earth but about as massive as the Sun. So a teaspoon of its material would weigh several tons, more than a pickup truck. A supernova is a huge explosion at the end of a massive star's life, and a massive star's core can survive a supernova as either a neutron star or a black hole. A star like the Sun ends as a white dwarf. A massive star ends with a supernova.

Words to know

• nebula: gas cloud
• supernova: star explosion
• protostar: baby star
• cinder: burnt leftover