1. Unit 2 The Earth in Space The Universe

2. “ A book of knowledge is spread out before us in the pageant of the heavens, but we cannot turn the pages. All we have managed to read is the first sentence of the first chapter, and even that we do not fully understand: it is written in a language foreign to us.” “ A book of knowledge is spread out before us in the pageant of the heavens, but we cannot turn the pages. All we have managed to read is the first sentence of the first chapter, and even that we do not fully understand: it is written in a language foreign to us.” (Inch and Stone, The Physical Environment, 1982, p.1)

3. Terminology Astronomy Astronomy The specific study of the universe, especially motion, positions, sizes, composition, and behavior of astronomical objects The specific study of the universe, especially motion, positions, sizes, composition, and behavior of astronomical objects Cosmology Cosmology The scientific study of the origins and nature of the universe The scientific study of the origins and nature of the universe

4. Measurement in Space Light Year Light Year The distance light travels in a year The distance light travels in a year Used as a measuring tool when the distances are too great Used as a measuring tool when the distances are too great 1 light year equals 9.46 x 10 12 km (9.46 trillion km) 1 light year equals 9.46 x 10 12 km (9.46 trillion km) How far is the Sun from Earth? How far is the Sun from Earth? 8 light minutes from Earth or 150 million km 8 light minutes from Earth or 150 million km

5. The Universe Everything that exists Everything that exists All that we see and touch, all energy, all the stars and planets, and all space All that we see and touch, all energy, all the stars and planets, and all space All the known cosmos All the known cosmos Most distant object sighted is 15 billions light years away Most distant object sighted is 15 billions light years away Diameter: Diameter: Infinite in size Infinite in size Mostly empty space Mostly empty space

6. Within the Universe Supergalaxy Supergalaxy Clusters of Galaxies Clusters of Galaxies Galaxies Galaxies Solar System Solar System Stars Stars Planets Planets Planetesimals Planetesimals Comets Comets

7. Supergalaxy Clusters of clusters of galaxies rotate around a central point Clusters of clusters of galaxies rotate around a central point Diameter Diameter 150 to 750 million light years 150 to 750 million light years

8. Clusters of Galaxies Systems contain hundreds of thousands of galaxies Systems contain hundreds of thousands of galaxies Galaxies orbit around a common center of gravity Galaxies orbit around a common center of gravity Diameter Diameter 5 to 50 million light years 5 to 50 million light years

9. Galaxies Based on the short video “The Structure of the Milky Way”, use complete sentences to answer the following question: Based on the short video “The Structure of the Milky Way”, use complete sentences to answer the following question: In your own words, compare a galaxy to a city. In your own words, compare a galaxy to a city.

10. Galaxies Systems of up to a hundred billion stars orbit around a common centre of gravity Systems of up to a hundred billion stars orbit around a common centre of gravity Composition Composition Gas, dust and billions of stars and planets Gas, dust and billions of stars and planets 4 types (based on shape) 4 types (based on shape) Spiral Spiral Bar Spiral Bar Spiral Elliptical Elliptical Irregular Irregular Diameter Diameter 35 to 100 000’s of light years 35 to 100 000’s of light years Most common one to us: the Milky Way Most common one to us: the Milky Way

11. Spiral Galaxy Andromeda Galaxy (M87) Andromeda Galaxy (M87) 2.5 million light years away in the constellation Andromeda 2.5 million light years away in the constellation Andromeda Contains about 1 trillion stars Contains about 1 trillion stars The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background objectAndromedaour Galaxy Once thought, this changed, now it is considered again to be the largest of the local group of galaxies (Andromeda, Milky Way, Triangulum and 30 other smaller galaxies) Once thought, this changed, now it is considered again to be the largest of the local group of galaxies (Andromeda, Milky Way, Triangulum and 30 other smaller galaxies)

12. Barred Spiral Galaxy Our galaxy, the Milky Way, has long been thought to be a spiral, with a Hubble sequence classification of Sbc (possibly SBb); recent research from the Spitzer Space Telescope, however, confirms that it is in fact a barred spiral. Our galaxy, the Milky Way, has long been thought to be a spiral, with a Hubble sequence classification of Sbc (possibly SBb); recent research from the Spitzer Space Telescope, however, confirms that it is in fact a barred spiral.Milky WaySpitzer Space Telescopebarred spiralMilky WaySpitzer Space Telescopebarred spiral Spins on its axis at a speed of 250 km/s or 900 000 km/h Spins on its axis at a speed of 250 km/s or 900 000 km/h 1 complete revolution takes 250 million years 1 complete revolution takes 250 million years

13. Barred Spiral Galaxy: Milky Way Galaxy The Milky Way system is a barred spiral galaxy consisting of over 400 billion stars, plus gas and dust arranged into three general components as shown to the left:Milky Way The halo - a roughly spherical distribution which contains the oldest stars in the Galaxy, The nuclear bulge and Galactic Center. The disk, which contains the majority of the stars, including the sun, and virtually all of the gas and dust http://cassfos02.ucsd.edu/public/tutorial/MW.html

14. Merging Galaxies http://heritage.stsci.edu/1999/41/index.html Trapped in their mutual orbit around each other, these two galaxies will continue to distort and disrupt each other. Eventually, billions of years from now, they will merge into a single, more massive galaxy. It is believed that many present-day galaxies, including the Milky Way, were assembled from a similar process of coalescence of smaller galaxies occurring over billions of years. Credit: NASA and The Hubble Heritage Team (STScI/AURA)