The Stars Chapter 14 Great Idea: The Sun and other stars use nuclear fusion reactions to convert mass into energy. Eventually, when a star’s nuclear fuel is depleted, the star must burn out.

The Nature of Stars Astronomy –Oldest science Star –Fusion reactor in space –Ball of gas All stars have a beginning and an ending

Measuring the Stars with Telescopes and Satellites Electromagnetic radiation Measurement of photons –Wavelength –Intensity –Direction –Variation

The Structure of the Sun Structure –Stellar core (hottest part, dense gas in a plasmic state) –Convection zone (rising gas from the core that cools) –Photosphere (the region from which externally received light originates) –Chromosphere (red color, thin layer, hotter and more dense than the photosphere) –Corona (external plasma atmosphere that extends hundreds of thousands or millions of miles into space) Solar wind –Stream of charged particles ejected from the upper atmosphere

The Sun's Chromosphere and Corona

Earth’s Magnetic Field

Northern Lights

The Sun’s Energy Source: Fusion Sun’s energy source Hydrogen (1 proton) converted to helium (2 protons) Life expectancy is 11 billion years, and the sun is currently 4.5 billion years

The Astronomical Distance Scale Time –Light-years (about 8,000 miles per second, or 6 trillion miles in 1 year) –The closest star to our sun is Proxima Centauri at 4.3 light years away (25.8 trillion miles) Measurement –Triangulation –Cepheid variable

The Hertzsprung-Russel Diagram Star groupings –Main-sequence stars –Red giants –White dwarfs

The Birth of Stars Nebular hypothesis –Pierre Laplace (gaseous clouds called nebulae rotate, cool, and gradually collapse and flatten due to gravity to form stars and planets)

The Eagle Nebula

Formation of a Planetary System

The Main Sequence and the Death of Stars Stars much less massive than the Sun –Brown dwarf –Glows 100 billion years No change in size, temperature, energy output

The Main Sequence and the Death of Stars – cont. Stars about the mass of the sun –Hydrogen burning at faster rate Move off main sequence –Helium burning –Red giant –Begin collapse –White dwarf

The Life Cycle of the Sun

Just how big are the stars?

The Main Sequence and the Death of Stars – cont. Very large stars –Successive collapses and burnings –Iron core –Catastrophic collapse Supernova

Star Explosion

Black Holes Black hole –Result of collapse large star –Nothing escapes from surface –Cannot see them See impact on other stars Detect x-rays, gamma rays

Cosmology Chapter 15 Great Idea: The universe began billions of years ago in the big bang and it has been expanding ever since.

Galaxies

Edwin Hubble and the Discovery of Galaxies Hubble –Largest telescope –Used Cepheid variable stars to measure distance to nebula Galaxies –Hubble discovered universe is billions of galaxies Cosmology

Kinds of Galaxies Spiral Elliptical Irregular and dwarf Active galaxies –Quasars

A Map of the Milky Way

A Typical Spiral Galaxy

A Typical Elliptical Galaxy

How BIG is the Universe??

The Redshift and Hubble’s Law

Redshift Hubble’s Law –The more distant a galaxy, the faster it recedes –V = H x d

Photographs of Galaxies and Their Spectra

What is the redshift??

Illustration of Hubble Expansion

The Big Bang

Big Bang –The universe began at a specific time in the past, and it has been expanding ever since

The Large-Scale Structure of the Universe The Local Group –Milky Way, Andromeda Galaxy, and others Groups, clusters, superclusters Voids

The Sequence of “Freezings”

10 –43 Second: The Freezing of All Forces Two fundamental forces –Gravity –Strong-electroweak force Limit of our knowledge of universe

Dark Energy

What is Dark Energy?