Starry Skies There are many more Stars in the Universe than there are grains of sand on all the beaches on Earth. Stars are the most visible, and numerous, objects in the night sky. Stars are giant spheres of superhot gas made up mostly of hydrogen and helium. Stars provide the light and heat we enjoy every day in addition to producing the heavy elements that nearly everything around us is made of – including you and me! We are all made of ancient stardust! What are stars made up of? Stars are mostly made up of two gases, hydrogen and helium. There are lots of layers inside a star, with gases moving around in each one. Why do stars glow? Stars get so hot by burning hydrogen into helium in a process called nuclear fusion. This is what makes them so hot and bright. Our Sun is a star. What are Star nurseries? New stars are born in star nurseries – huge cloud of gas and dust know as nebulae. How stars are born? The gasses in the nebula gradually gathers together into spinning balls. They spin more and more quickly, until they get amazingly hot and big blast, called a nuclear reaction, begins. When this happen, a baby star begins to glow. The exact lifetime of a star depends very much on its size. Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years. Smaller stars, however, will last for several billion years, because they burn their fuel much more slowly. Life Cycle of a Star Gravity pulls together little knots of dust and gas inside the nebulae. Each one could become a star, as gravity squeezes it tighter and it becomes hotter. The hydrogen fuel that powers the nuclear reactions within stars will begin to run out, and they will enter the final phases of their lifetime. Over time, they will expand, cool and change color to become red giants. Small stars, like the Sun, will undergo a relatively peaceful and beautiful death that sees them pass through a planetary nebula phase to become a white dwarf, which eventually cools down over time and stops glowing to become a so-called "black dwarf" also called as dead star. Massive stars, on the other hand, will experience a most energetic and violent end, which will see their remains scattered about the cosmos in an enormous explosion, called a supernova. Once the dust clears, the only thing remaining will be a very dense star known as a neutron star, these can often be rapidly spinning and are known as pulsars. If the star which explodes is especially large, it can even form a black hole. Starshine Our Sun is a star that is halfway through its life. In the life cycle it would sit between being formed within a nebula and becoming a red giant. Types of Stars Stars that are in their main sequence (normal stars) are categorized by their color. The smallest stars are red and don't give off much of a glow. Medium size stars are yellow, like the Sun. The largest stars are blue and are hugely bright. The larger the main sequence star, the hotter and brighter they are. Dwarfs - Smaller stars are called dwarf stars. Red and yellow stars are generally called dwarfs. A brown dwarf is one that never quite got large enough for nuclear fusion to occur. A white dwarf is the remnants of the collapse of a red giant star. Giants - Giant stars may be main sequence stars like a blue giant, or stars that are expanding like red giants. Some supergiant stars are as big as the entire Solar System! Neutrons - A neutron star is created from the collapse of a giant star. It's very tiny, but very dense. Shapes in the Sky: Constellations are groups of stars that can be seen from Earth. They all have names – often related to their shapes.
