The History of the Universe The Big Bang Theory Hydrogen in the Universe What are Galaxies The Milky Way

The Big Bang Theory Before the Big Bang, there was no universe as we know it. Suddenly a dense, hot, fireball of space, energy and matter exploded moving outwards. This fireball occurred 14- 15 billion years ago,. forming protons, neutrons and electrons. As the universe expanded, the matter gathered into clumps. These clumps evolved into stars and galaxies.

Hydrogen in the Universe Hydrogen was the simplest element forming with one proton. Hydrogen makes up more than 90% of the universe. Hydrogen is the primary fuel burned by young stars like our sun.

The Life of a Star A star is born when gravity pulls hydrogen atoms together until they fuse and release enormous amounts of energy. A star dies when hydrogen fuel is used up and the gravity causes the star to collapse.

What is a Galaxy? Galaxies are enormous swarms of stars, dust, gas, and dark matter held together by gravity. Most galaxies are found in clusters of about 150 galaxies, bound together by each other’s gravity. Galaxies range in size, containing anywhere from 100,000 to 3 trillion stars!

Galaxy types: Spiral galaxies – Disk shaped; Nucleus of stars, with flattened arms Parts: nucleus; disk; halo; Contains young and older stars

smaller than spiral galaxy 60% of all galaxies are this contains older Elliptical galaxies- smaller than spiral galaxy 60% of all galaxies are this contains older stars

Irregular galaxies – No particular shape Consists of young stars

Where are We in the Milky Way?

Understanding a Light Year A light year is the distance light travels in one year. Light traveling in one year equals about 5,878,786,100,000 miles or 9.5 trillion kilometers Light you see when you look at a star came from the star in the past. Light from our sun takes 8 minutes to travel through space.

Milky Way Galaxy It is a barred spiral galaxy. It takes light 100,000 years for light to cross from one side of the Milky Way to the other. This is its diameter It is made up of at least 100,000,000,000 stars (one hundred billion) with gases and dust

Galaxy Neighbors of the Milky Way: The Andromedia Galaxy which is 2.9 million light years away. This is a spiral galaxy like the Milky Way. Two irregular galaxies are near the Milky Way; Large Magellanic, Small Magellanic The Sagittarius Dwarf galaxy is very small but is colliding into our galaxy.

Where is our solar system on the Milky Way? Our sun and planets are located about 30,000 light-years from the Milky Way’s nucleus (the center). It is about two-thirds away from the center of the galaxy. Our solar system is on the Orion arm. Our sun and planets orbits around the center of the Milky Way. It takes 225 million years!

Stars in the Milky Way close to Earth: The nearest star to our solar system that is visible to the naked eye is Alpha Centauri (4.34 light years) The nearest star to our solar system that is not visible to the naked eye is Proxima Centauri ( 4.24 light years)

Seeing the Milky Way! If you lived in the southern hemisphere, If you see a creamy strip across the sky on a moonless night, you’re looking out at the outer edge of the Milky Way. If you lived in the southern hemisphere, you’d be looking into the center of the Milky Way.