The Universe Electromagnetic Radiation Light that travels directly

The Universe

Electromagnetic Radiation • Light that travels directly through space in the form of waves – electromagnetic radiation.

Tools of Modern Astronomy • Astronomers today use tools that help them to study the universe. – Telescopes – collect and focus different types of electromagnetic radiation, including visible light. • Types: – Visible light telescope – Radio telescope

Tools of Modern Astronomy – Satellites – telescopes that orbit the Earth, outside Earth’s atmosphere, and can detect x-rays, UV rays and gamma rays that would otherwise be blocked. • Hubble Space Telescope The Hubble Space Telescope: 5: 04 min

Orion Nebula

Crab Nebula

Galaxy M 74

Young Star Forming

Centaurus A

The Universe • The Sun, Planets and Moons make up our Solar System. – Our solar system is one of many that make up our Galaxy, The Milky Way. • The Milky Way is one of many galaxies that make up the Universe. • Because the universe is so expansive we measure the distance from one object to the next in light years.

Light Years • The distance that light travels, through space, in one year = light year. – 300, 000 km/sec or 9. 5 million km • Our closest star, Proxima Centauri, is 4. 2 light years away. – It takes the light from Proxima Centauri 4. 2 years to reach Earth

Classifying Stars • A star is a huge sphere of glowing gas. – Consist of mostly hydrogen (H) and Helium (He) – Make energy by nuclear fusion • The sun is an average-brightness star • Astronomers classify stars according to their physical characteristics: – Size – Temperature – Brightness

Star Size Star Temperature • Stars range in size: • A star’s color reveals its temperature. – Neutron star – smallest, about 20 km in diameter – White Dwarf Star • ½ the size of Earth – Medium-sized Star • Our Sun – Giant Star – Supergiant Star • Betelgeuse – If it took the place of our sun it would extend past Jupiter. – Cool stars • Reddish (3000°C) to Redorange (4, 500°C) – Warmer stars • Orange (5, 000°C) to white (10, 000°C) – Hot stars • Blue-white (20, 000°C) to Blue (50, 000°C)

Temperature: Color: Red (Cool) Yellow (Warm) White (Hot)

Star Brightness • The brightness of a star depends on its size and temperature. – How bright a star looks from Earth - Apparent Magnitude. • The closer the star the brighter it is – How bright the stars would be if they were all at a standard distance from Earth – absolute magnitude.

Hertzsprung-Russell Diagram • The two most important characteristics of stars are the temperature and the absolute magnitude. – Plotted against each other you get the H-R Diagram • 90% of all stars are main-sequence stars • Giants and supergiants are bright but low temperature • White dwarfs are hot but not very bright

Increasing Brightness H-R Diagram (°C)

Death Lifecycle of a Star Birth

Lifecycle of a Star • Just like humans, stars have lifecycles. – They’re born, grow, become middle aged and then die. • Birth = Nebula – Lots of gas over a large volume » Gravity pulls some of the gas and dust into a Protostar • Proto in Greek = “earliest” – When nuclear fusion begins a star is born! – How long a star lives depends on its mass » Smaller stars live longer (200 billion years) • Burn through their fuel slower » Medium stars (10 billion years) » Large stars (10 million years).

Death of a Star • Middle Aged = when a star begins to run out of fuel, the center shrinks and the outer parts expand becoming a red giant or supergiant. • Death - Once the fuel runs out completely it becomes a white dwarf, neutron star or black hole. 1. White Dwarfs – small to medium mass stars, 10+ billion years old. • About ½ the size of Earth with as much mass as the sun. • When a white dwarf stops glowing, from left over energy, it becomes a black dwarf.

Death of a Star 2. Neutron Star – a dying giant or supergiant that suddenly explodes, supernova. • Material left over from an exploding supernova becomes a neutron star. – Smaller and denser than white dwarfs. 3. Black Holes – the most massive star. • Contain more than 40 times the mass of the sun. – After exploding to become a supernova the gravitational pull is so large that it pulls the gases inward to the point nothing can escape, not even light.

Galaxies • Our solar system belongs to the Milky Way galaxy. • There are billions of galaxies in the universe. – 3 main categories: 1. Spiral galaxies – The Milky Way 2. Elliptical galaxies 3. Irregular galaxies

Galaxy Categories Irregular Galaxy Spiral Galaxy (Milky Way) Elliptical Galaxy

Big Bang Theory • Roughly 10 -15 billion years ago the universe formed as an enormous explosion. – Its been expanding ever since and is a billion times larger than it was at the beginning.