Space isn't as empty as you might think. In fact, the area between the stars is laced with gas and small dust particles. In places, this stuff collects into clouds, called nebulae. A typical nebula contains about 74% hydrogen, 25% percent helium, and 1% heavier elements.

Nebulae are where new stars form, but not all nebulae are destined to become a new stellar nursery . . . it all depends on the temperature and the density of the cloud. Gravity works to pull the gas and dust together, but the material itself exerts an outward pressure. The warmer the material, the more active it is, and the harder it pushes.

In certain types of nebulae, where the temperature is cool enough, the force of gravity overcomes the outward pressure. The gas and dust becomes more tightly packed, and eventually collapse to form one or more clumps of material. Scientists call these protostars.

And if all goes well, the battle between thermal pressure and gravity will transform a protostar into what scientists call a main-sequence star. For this to happen, the temperature has to rise enough at the core of the protostar to trigger a fusion reaction, the thermonuclear process that converts hydrogen to helium and powers all stars, including our sun.

The heat from the fusion creates thermal pressure that keeps the bulky mass from collapsing under its own weight. Once this balance is achieved, the star can shine for billions of years.

Many other types of nebulae are within easy reach of binoculars and small telescopes. They can be split into two main types, based on their general appearance: dark nebulae and bright nebulae. Dark nebulae appear as black voids in the sky, blocking and obscuring background stars. Bright nebulae appear as faint glowing regions. They emit their own light or reflect the light from nearby stars.