1. What is the structure of the universe? The universe consists of super clusters of galaxies separated by vast, bubble-shaped voids. Each super cluster consists of up to several hundred-galaxy clusters, and each galaxy cluster may contain up to several thousand individual galaxies. The galaxy super clusters are thought to be arranged in the shape of winding filaments that may be hundreds of millions of light years long. The most remote parts of the Universe are believed to be about 15 billion light years away and are moving away from our own galaxy at close to the speed of light.

2. The Structure of the Universe

3. Evidences of the Big Bang The big bang is a theory that the universe originated as a single mass, which subsequently exploded. The best evidence for the Big Bang theory is the existence of cosmic microwave background radiation. This is very faint radiation that appears to come from all parts of the Universe. Some of these galaxies are 13 billion light-years away, which means that the light we see from them has taken 13 billion years to reach us. These galaxies appear to be more tightly packed than closer galaxies, which would indicate that the Universe is expanding in volume as it gets older and was once much smaller and denser.

4. GALAXY A Galaxy is a vast cluster of stars held together by gravity Galaxies formed out of enormous, swirling clouds of gas that developed after the universe was born. Astronomers estimate that there are about 100 billion galaxies in the universe, and that each galaxy contains, on average, 100 billion stars. Galaxies are huge: it takes thousands of light years for light to travel from star to the other side of a galaxy.

5. TYPES OF GALAXIES Spiral galaxies - have central lens-shaped, and made of billions of stars. Milky Way & Andromeda are spirals. Elliptical galaxies - ranged from nearly spherical to lens-shaped. Their brightness patterns show that most of their stars are close to the center Irregular galaxies - are smaller, fainter and less common than the others. Their stars are spread unevenly

6. Light Year A light year is the distance light travels in one year. One light year is estimated as 6 trillion miles (9.5trillion km) The speed of light is 300,000km/s or 300,000,000m/s In one year light can travel about 10 trillion km In the universe, the km is too small to be useful. Example, the distance to the nearest big galaxy, Andromeda is 21 Quintillion (2.1x 10 19 km) Astronomical units (AU) is used within our solar system. Example, Mercury is 1/3 AU from the Sun

7. Supercluster galaxies within 200light years, and nearby galaxies

8. Light Year - Continued Distances to other parts of our galaxies, Astronomers use units of light years (parsec). 1 parsec = 3.3 light years The Milky Way Galaxy is about 100,000 light years across The Andromeda Galaxy is about 2.3 million light years away Distance from Earth to Proxima Centauri, the nearest star is about 4.24 light years.

9. The Universe within 100 million Light Years The Virgo Supercluster

10. Nova and supernova of a star In a nova, only the stars surface explodes. Most white Dwarfs are Nova In a supernova, the star’s core collapses and explodes. Neutrons stars results from supernova

11. Supernova Event Supernova is an explosion of star that increases in brightness many thousands times. The most spectacular supernova in our modern is the Megallanic clouds that occurred in 1987. Astronomers believe that in the core of a supernova, the forces are so great that every atoms electrons are crushed into its nucleus. The collapse electrons combine with protons to form neutron stars A neutron star is only about 10 km in diameter and trillion times more dense than the Sun.

12. The Megallanic clouds- Supernova