Astronomy, part 04 : Stars.

04 Stars

A star is simply a space object that emits energy in the form of heat and light and is composed of gas and dust attracted to each other via the force of gravity.

As dust and gas get closer together, temperatures in the star’s core get so hot that the nuclei of the atoms begin to fuse together.

Two hydrogen atoms combine to form a helium atom. This reaction is called nuclear fusion and creates an enormous amount of energy. This energy is transmitted throughout space in different wavelengths of light that we call electromagnetic energy.


Here we go. Birth to death, and oh, what a glorious event a star’s death can be!

  1. Nebula

    1. Picture this: a little cloud of dust and gas - a nebula -  floating through space.

    2. Gravity gently, violently, inevitably pulls them together as time passes. It gets smaller as gravity does her number; a process called condensing.

    3. At this point, the condensing nebula becomes a protostar.

  2. Nuclear fusion

    1. The nebula’s getting smaller. It’s getting hotter and hotter until it’s so hot that the process of changing from hydrogen to helium begins...boom.

    2. This fusion releases energy in the form of light and heat, which…

    3. ...forms a star.

  3. Main sequence star

    1. The fusion creates an outward pressure that counterbalances gravity’s force (that is pulling it inward). This fusion continues as long as the hydrogen at its core is fueling it. Could be a few million years. Could be several billion years. Who knows? Depends a lot on the size of the star.

  4. Giant / Supergiant

    1. A medium-sized star converts its hydrogen to helium, which - remember! - is fueling its energy. As it starts to run out, it begins cooling.

      1. The cooling reduces the outward pressure from the fusion, causing the core to contract.

      2. As the core contracts, its temperature increases, and the outer layers expand, cool, and get broken off into space.

      3. A star at this phase is called a giant.

    2. A big-sized star does the same sort of thing, except instead of forming a giant at the end, it forms a…

      1. Supergiant.

      2. When the core of a supergiant becomes insanely hot from getting so compressed, guess what?!

      3. It starts the fusion reaction.

    3. At that point, a

      1. Giant becomes a white dwarf.

        1. After a giant’s helium is gone, what remains is a super-dense hot core. That’s what we call a white dwarf.

        2. When it cools down and no longer emits light, it’s called a black dwarf.

Supergiant becomes a supernova. Here’s how it works:

  1. Remember, a supergiant is a gigantic star. When it compresses, it compresses fast and its core temperatures get really really hot. Large elements begin to fuse in the core, which form heavier elements such as…

  2. ...Iron.

  3. Iron can’t release energy via fusion. So…

  4. ...that iron makes the core collapse. Collapse violently. That collapse sends shockwaves throughout the star and creates a massive explosion of light called…

  5. ...a supernova!

  6. After the supernova collapses on itself, it contracts into a super duper dense ball, a neutron star, because neutrons are the only thing that can exist at its core.

  7. This causes smaller supernovas to form because neutrons can resist gravity’s force that’s pulling the supernova together.

  8. In supersize supernovas, gravity is so powerful that nothing can prevent it from collapsing. Gravity sucks everything in. Everything. Including light. We call this a…

  9. hole.

  10. Wow.

Now, super cool part coming up: when gas and dust get thrown off a starts to form new nebulas. In other words, the process starts all over again! Wow and wow.


You might think that stars are all the same color. Wrong. They’re not. They all give off different light. Why? Because different stars give off different types of energy, which affects the colour of the light they emit. The type of energy they give off depends on different things - mainly which type of star they are and what stage they’re in.

As the temperature increases, the light gets brighter and more blue.

As the temperature decreases, the light gets dimmer and more red.

There are exceptions, such as with white dwarfs and giants, but we’ll swing back around to those later. Basically, their temperatures are not related to their brightness.


Is there a pattern to the stars in our skies? It’s sure fun to look for them. We call these groupings of stars that appear in different shapes constellations.

The most famous one is The Big Dipper, which is part of the larger constellation Ursa Major in the northern sky.

Think of constellations as being like maps laid out in the night sky. People have used them for centuries to help guide their travel. Ah ha, so that’s how people didn’t get lost before GPS and Google Maps!

Polaris is the name for the North Star, which is directly above the North Pole. If you can find the North Star, you can always get your bearings and figure out where you are on Earth. At least that’s the idea.

Sun’s layers

The sun is a star. A rather important one to those of us still living on Earth.

The official description for the sun is this: a medium-sized main sequence yellow dwarf star at the center of our solar system. Love that.

Our sun is unique in that it’s far away from other stars. Most others are hanging out in clusters or are orbiting each other. But lucky us, we got the sun hanging out in the middle, keeping us all warm and giving us bright natural luminance to properly put on eyeliner and read Roald Dahl  books on the beach.

The sun has four layers: core, radiative zone, convective zone, atmosphere.

The core is where helium forms, as with other stars, through the fusion of hydrogen. The fusion of this helium is what produces light and heat.

The radiative zone. Energy goes from the core to here.

The convective zone is where gases circulate and swirl the energy around in currents. What kind of currents? Convection currents!

The atmosphere. The sun’s goes out several million miles outward.

FOOTNOTE: Introduction to a ten-unit survey of Astronomy and the foundations of the universe beyond our world.

Education for most ages and for all curious people. Written by Joseph Ivan Long with curiosity, humbleness, and a big grin.