The Universe PHYSICAL SCIENCE Our Place in the Universe Scale of the Universe

Exploring the Universe  Star – a large glowing ball of gas in space  Generates energy through nuclear fusion in its core  The Sun is the closest star to use, and is of fairly average size  Formed by gravity  Why do stars have to be massive in order to be a “star”?  Distances to the Stars  Space distances are so huge normal units aren’t very useful  Light-year (LY) - The distance that light travels through a vacuum in one year  Astronomical Unit (AU) – 1 AU = Distance from Sun to Earth = 93 million miles  How do we measure the distance to the stars?

How to measure distance to a star  Parallax – Triangulation Parallax – Triangulation  Only works on stars within 400 ly  Look at a star when Earth is in two diff positions and see how its position relative to the stars behind it change  Scientists have developed other ways to estimate distances to further stars

Properties of Stars  Astronomers classify stars by their color, size, and brightness  Color  Indicates stars temperature  Red – Coolest Blue- Hottest

Star Color  Color and Temperature  A star’s color indicates the temperature of its surface.  The hottest stars, with surface temperatures above 30,000 K, appear blue.  The surfaces (photospheres) of relatively cool red stars are still a toasty 3000 K or so.  Stars with surface temperatures between 5000 and 6000 K appear yellow, like the sun.

Spectral Classes of Stars

Star Brightness  Apparent Brightness  How bright it looks from Earth  Absolute Brightness  How bright it actually is  It’s like measuring the brightness of all the stars when they are all equally far from you  Size and temperature  Light becomes fainter with distance

Size & Mass  Once astronomers know a stars temperature and absolute brightness, they can estimate its diameter and then calculate volume  Scale of the Stars Scale of the Stars  Scale of the Universe Scale of the Universe

Hertzprung- Russel Diagram  Used to estimate sizes of stars and their distances, and to infer how stars change over time  90% of all stars found on main sequence  Relates brightness, Temp, Size, & Color

Composition of Stars  Absorption Lines  Scientists determine the chemical makeup of stars by looking at Absorption lines  Spectrograph – instrument that spreads light from a hot glowing object into a spectrum  Different elements absorb different wavelengths of light. Thus removing them from the spectrum. The blank spaces (absorption lines) in the spectrum below represent different elements in that star  Each star has its own unique spectrum.  Most Stars have a chemical makeup that is similar to the Sun, with H and He together making up 96 to 99.9% of the stars mass

Why are Stars Round?  Gravity tries to get everything as close to the center as possible…. The only way to achieve this is if it is in a spherical shape  Star’s are held in balance by Two Forces  Gravity - Pulls star inwards  Thermal Pressure from Nuclear Fusion– Pushes star outward  The relative strength of these determine the stars size.  These two forces are balanced before a star dies  Nuclear Fusion – Two atoms are pushed together so hard they ‘fuse’ into one and create a different element

Life Cycle of stars

Death of a Star  Low & Medium Mass Stars  Planetary Nebula  White Dwarf  High Mass Stars  Supernova  Neutron Star  Black Hole

When a star dies….  White Dwarf (C.P. Powerpoint)  Neutron Stars  Black Holes

Groups of Stars  Galaxy  Huge group of individual stars, star systems, star clusters, and gas bound together by gravity  Our Galaxy – Milky Way  Each consists of Billions of stars…. Sometimes Trillions  Four types – Spiral, Barred-Spiral, Elliptical, Irregular

Location of solar system Central bulge Nucleus Overhead View of Our Galaxy Disk of spiral arms containing mainly young stars Central bulge containing mainly older stars Nucleus Halo containing oldest stars Side View of Our Galaxy

Big Bang Theory  Explanation  The universe came into existence in a single moment, an event called the Big Bang  The event happened 13.7 Billion years ago  All matter and energy were concentrated into a single infinitely small point  Timeline of the universe Timeline of the universe  Video Video Big bang occurred 13.7 billion years ago. First stars and galaxies formed 200 million years after big bang. Solar system formed 4.6 billion years ago. Earth today

Evidence for Big Bang  Edwin Hubble -Red Shift of Galaxies  Light from most galaxies undergoes a redshift. Light is experiencing Doppler effect and shifting to longer wavelengths (red light). This means it is moving away from us. This is noticed in most galaxies.  Shows universe is expanding  By looking at the rate its expanding we can calculate how long its been expanding, thus inferring the age of the universe  More distant galaxies are moving away from Earth faster than closer galaxies  Cosmic Microwave Background Radiation  Video – Evidence for Big Bang CMB Video – Evidence for Big Bang  Video – Red Shift of Galaxies Video – Red Shift of Galaxies  Rubber band activity Pg. 855 Doppler Effect with Light Waves Stationary Moving towards Moving away

Continued Expansion  All galaxies are expanding away from all other galaxies  Further way the galaxy the greater the expansion  Will Universe continue expanding forever??  Recent evidence shows that the rate of expansion is actually increasing

Cosmic Microwave Background Radiation  Faint distant glow detected in every direction  Energy produced during the big bang still travelling through the universe

Matter in the Universe  Dark matter  Matter that does not give off light  Cannot see it but we know its there because of its gravitational effects