1. OUTER SPACE Other Components of the Universe

2. 2 T The most common type of celestial object astronomers see in space are stars. Most stars appear to be gravitationally bound together into groups The following categories describe various types of star groupings:

3. STAR CLUSTERS All galaxies contain star clusters which are groups of stars that: Develop together from the same NEBULA Are gravitationally bound Travel together

4. STAR CLUSTERS There are two types of star clusters: Open star clusters are collections of six to thousands of usually young stars Globular clusters are ball-shaped collections of thousands to millions of very old stars There are approximately 20 000 open star clusters found within the main disc of the Milky Way.

6. TYPES OF GALAXIES Galaxies are collections of millions to hundreds of billions of stars, planets, gas, and dust, measuring up to 100 000 light years across. They come in different shapes and sizes and are spread across the Universe

7. ELLIPTICAL GALAXY  Spherical or flattened oval shape  Older galaxy  Very little gas, dust, or young stars More than half of all galaxies we can see

8. SPIRAL GALAXY  Spinning flattened disc with a central bulge and 2-4 spiral arms  Central core: made up of old stars Spiral arms: made up of gas, dust and young stars

9. BARRED SPIRAL GALAXY  Subclass of spiral galaxies  Spinning flattened disc with a central bulge and 2-4 spiral arms BUT have a central bar pattern running down the centre  Central core: made up of old stars Spiral arms: made up of gas, dust and young stars

10. LENTICULAR GALAXY  Central bulge surrounded by a flattened disc of gas and dust  NO spiral arms  Are spiral galaxies that have lost their gas and dust  Made up of older red stars

11. IRREGULAR GALAXY  No definite shape  Have MORE gas and dust than spiral galaxies  NO central bulge or spiral arms 100 million- 10 billion stars

12. The Milky Way  Consists of more than 200 billion stars and is more than 100, 000 ly across  The sun lies 30, 000 ly away from the centre of the galaxy  Is a barred spiral galaxy with two spiral arms. The central bulge is a huge collection of old stars. It is surrounded by spinning disc of newer stars and clumps of gas and dust.  Our solar system is located on the inner edge of one of the spiral arms.  A massive black hole is located at the centre of the Milky Way

13. Galaxy Clusters  The Milky Way is part of a group of more than 35 galaxies.  Our largest and closest galaxy is the Andromeda galaxy (a spiral galaxy consisting of at least 300 billion stars)  Astronomers and the University of Toronto believe that the Milky Way and Andromeda may collide in approximately 5 billion years!

14. The Origin of the Universe

15. Edwin Hubble – The Expanding Universe Edwin Hubble devised a classification system for galaxies and categorized than content, distance, shape, and brightness. He noticed that there were redshifts in the emission of light from many dimly lit galaxies and realized that these were moving away from each other at a rate constant to the distance between them. He used this to formulate Hubble's Law (1929) which helped astronomers determine the age of the universe and develop the idea that the universe was expanding.

16. Monsignor Georges Lemaître – The Big Bang Theory It was a Belgian cosmologist and priest first proposed the idea that the universe was created from a single point of infinite density which later became known as the Big Bang theory. Fr. Lemaître first trained as a civil engineer. In the First World War, he served in the Belgian army as an artillery officer. In 1923, he entered a seminary, and later became an ordained as a Jesuit priest.Big Bang

17. After his ordination, he went to Cambridge University, in England, and M.I.T., in Boston, (1923-1926) to study physics. It was in Boston where he was influenced by ideas about the expanding universe proposed Edwin Hubble and Harlow Shapley. He returned to Belgium in 1927 where he was appointed to the position of professor of astrophysics at the University of Louvain.HubbleShapley

18. In 1933 Fr. Lemaître published “Discussion on the Evolution of the Universe”, in which he proposed the universe began as a “primeval atom” a region of space about 30 times larger than the Sun that contained all the material in the Universe. He proposed that it exploded releasing matter in all directions leading to the present Universe. This is the first time that anyone had proposed that there was an initial event to start the expansion.

19. Fr. Lemaître travelled to a conference in California in 1933 where Albert Einstein publically remarked “This is the most beautiful and satisfactory explanation of creation to which I have ever listened.”

20. Fr. Lemaître published his Hypothesis of the Primal Atom in 1946. In the same year, George Gamow a Russian physicist, who had defected to the United States in 1934, and his colleagues began to develop the nuclear physics of the Big Bang at George Washington University. Work is still continuing at Universities and other research institutions around the world today.Gamow

21. ORIGIN OF THE UNIVERSE: The Big Bang Theory  Time zero estimated at being 10-15 billion years ago  At that time all matter was packed into a small, dense, hot mass under pressure (smaller than the period at the end of a sentence!)  The Big Bang describes the beginning of the Universe as we know it  Changing our theories about the universe is a continuing process, as scientists try to explain new discoveries