1. Option E.1 Introduction to the Universe

2. Collection of planets, moons, asteroids, comets, and other rocky objects travelling in elliptical orbits around a star or star system under the influence of its gravity Solar System

3. Sun Inner Planets Asteroid Belt Outer Planets Kuiper Belt Objects/Ort Cloud Structure of our Solar System

4. Structure of Solar System

8. Relative Planet Sizes We could fit 1000 Earths inside Jupiter We could fit 1000 Jupiters inside the Sun It would take one million Earths to fill the Sun All of the other planets could fit inside Jupiter at the same time

9. All of the planets orbit the Sun Elliptical orbit with the sun at one of the foci Nearly Circular Very average star in size, temperature, mass, age LOTS more about stars later Our Star

10. The four protoplanets closest to the sun became Mercury, Venus, Earth and Mars They all contained large amounts of heavy elements, like iron and nickel They lost their less dense gases because gravity was not strong enough to hold them Lighter elements were boiled away by the sun As the denser material sank to the center of the planets, layers formed The less dense material was on the outer part, and the denser material was at the center The inner planets are smaller, rockier and denser than the outer planets Inner Planets

11. Asteroid Belt Asteroid: a small, rocky object, without an atmosphere, that orbits the sun Asteroids are material left over from the formation of the solar system Remains of a planet that was destroyed in a collision long ago OR material that never condensed into a planet Most asteroids are located in a band between the orbits of Mars and Jupiter Can be large (bigger than Pluto) Considered ‘minor planets’ or ‘dwarf planets’ Can even have moons of their very own

12. Outer Planets The next four protoplanets became Jupiter, Saturn, Uranus and Neptune These outer planets are much different than the small, rocky inner planets They formed in colder regions of the solar nebula Sun did not boil away their lighter elements, H & He Also kept their ices (water, methane and ammonia) At first, thick layers of ice surrounded small cores of heavy elements Because of the intense heat and pressure in the core, the ices melted to form layers of liquids and gases Today, these planets are referred to as gas giants They are composed a lot of gas, have low density, and are huge planets

13. Pluto was the farthest planet from the sun Unlike the other planets, Pluto is very small Smallest planet, smaller than the moon Like the gas giants, Pluto is very cold Pluto can be best described as an ice ball made of frozen gases & rock Pluto’s orbit is elongated and tilted Does not fit with other planets Classified as minor planet Pluto & the Kuiper Belt

14. Scientists have discovered hundreds of objects beyond Neptune’s orbit The Kuiper belt contains small bodies that are made mostly of ice Pluto has more in common with the objects in the Kuiper belt than the other planets in the solar system Pluto & the Kuiper Belt

15. Irregular objects comprised of frozen gases, rock and dust Have very elliptical orbits Orbital periods range from a few to thousands of years Have tails when near sun Point away from sun Caused by sun vaporizing part of the comet Comets

16. When comparing distances on the astronomical scale, it can be quite harmful to remain in SI units Possible other units include the Astronomical unit (AU), the Parsec (pc) or the light year (ly) The distance from the earth to the sun is defined as one Astronomical Unit 1 AU = 1.5 ×10 11 m The light year is the distance traveled by light in one year 1 ly = 9.46 x 10 15 m ≈ 10 16 m The nearest star to our sun is about 4 light years away Our galaxy is about 100,000 light years across (≈10 21 m) The nearest galaxy is about a million light years away The observable universe is about 1.5 Billion light years across (≈ 10 26 m) Astronomical Units

17. Astronomical Conversions 1 AU = 1.496 x 10 11 m 1 l y = 9.46 x10 15 m = 9.5 ×10 15 m ≈ 10 16 m 1 l y = 63240 AU = 9.5 ×10 15 m ≈ 10 16 m 1pc = 3.086x10 16 m 1pc = 3.26 l y 1pc = 2,06265 AU = 2.063x10 5 AU

18. Astronomical Distances ObjectApprox. Distance From Earth (ly) Moon4 x 10 -8 Sun1.6 x 10 -5 Nearest star (Proxima Centauri) 4.3 Center of Milky Way3 x 10 4 Nearest Galaxy2 x 10 6 Farthest Galaxies10

19. Intergalactic cloud of gas and dust Birthplace of stars (stellar nurseries) Created by big bang or death of stars Nebula

20. A group of stars that are physically close to each other in space Created at the same time by the collapse of the same nebula Open Cluster Contain up to several hundred to thousands of stars Younger than 10 billion years old Can contain some gas and dust Globular Cluster Contain many more stars (10,000) Older than 11 billion years old Contain very little gas or dust Usually spherical in shape Stellar Clusters

21. Almost all the ancient civilizations took a keen interest in the night sky Stars were grouped into fixed patterns known as constellations Constellations are groups of stars in the night sky that appear to be close to each other Not true in most cases Constellations

22. Viewed for a whole night, stars seem to rotate around one star, Polaris (Pole star or North Star) Effect due to rotation of Earth about its own axis Constellations Night sky will also change seasonally due to the rotation of the Earth around the Sun Shown from modern measurements that some stars appear to be moving relative to each other Will affect the shape of constellations over periods of 100,000 years

23. A galaxy is a collection of a very large number of stars mutually attracting each other through the gravitational force The number of stars varies between a few million and hundreds of billions There approximately 100 billion galaxies in the observable universe Astronomers classify galaxies by shape There are three main types: 1.Irregular 2.Elliptical 3.Spiral Galaxies

24. Have no particular shape Least common type of galaxy Usually have low total masses Contain a lot of dust and gas Contain large numbers of young stars Can form when galaxies collide Irregular Galaxies

25. Elliptical Galaxies Nearly spherical to very elongated Have extremely bright centers Do not have spiral arms Contain few young stars and mostly old stars Contain little dust and gas

26. Spiral Galaxies Has a nucleus of bright stars and flattened arms that spiral around The spiral arms contain a lot of young stars, gas and dust Most of the galaxies close to us are spiral The Milky Way is spiral

27. The Milky Way It is a spiral galaxy Diameter of 100,000 light years Thickness of 3,000 light years The diameter is equal to nearly 20 million solar systems The Milky Way can be seen on a very dark night as a bright band stretching across the sky

28. The Milky Way Our Sun is located in one of the spiral arms, called the Orion arm At a distance of about 30,000 light years from the center The sun is about two-thirds of the way to edge Every star orbits around the center The Sun orbits the galactic center approximately once every 250 million years At the galactic center, there is thought to be a giant black hole

31. Galaxies are grouped together in galaxy clusters Held together by mutual gravitational attraction Our local galaxy cluster is made up of around twenty galaxies including the Large Magellanic Cloud and the Andromeda galaxy Nearest galaxy cluster to us is the Virgo cluster at a distance of 5.9x10 7 ly Possibly 2000 galaxies Bigger galaxy cluster contain up to 10,000 galaxies Clusters are grouped into superclusters Spread over distances of 10 8 ly Superclusters form into filaments leaving vast voids of empty space between them Galaxy Clusters