Introduction to Astrophysics

Defining the difference between astrophysics and astronomy; studying the vast range of scales in astrophysics; getting the big picture in a breathtaking series of exponential jumps from the Earth to countless clusters of galaxies.

Zooming in on the microcosmos; why elementary particles are just as central to astrophysics as stars and galaxies; reviewing the four fundamental forces of nature; performing a calculation that explains why atoms have to be the size they are.

How astrophysicists map the universe; focusing on the tricky problem of calculating distances; how a collection of overlapping techniques provide a "cosmic distance ladder" that works from nearby planets to stars and far distant galaxies.

The connection between Isaac Newton's laws of motion and the earlier laws of planetary motion discovered empirically by Johannes Kepler; Kepler's third law is the ideal method for measuring the mass of practically any phenomenon in astrophysics.

Discovering the law of gravity just as Newton might have; analyzing Kepler's laws with the aid of calculus; a graphical method for understanding orbits; the conservation laws of angular momentum and energy in light of Emmy Noether's theory.

Learning why the rings around Saturn and the much fainter rings around Jupiter, Uranus and Neptune are roughly at the same relative distances from the planet; knowing why large moons are only found in wide orbits; an analysis of tidal forces.

Using analytical skills to probe the strange properties of black holes; calculating the Schwarzschild radius, which is the boundary beyond which no light can escape; determining the size of the giant black hole at the center of our galaxy.

Investigating electromagnetic waves, which consist of photons from gamma-ray to radio wavelengths; a dense collection of photons is comparable to a gas obeying the ideal gas law; this law, together with other laws, explains the cosmos.

Surveying representative planets in the solar system with an astrophysicist's eyes; knowing why Mercury does not have an atmosphere and why Venus is so much hotter than Earth; analyzing such riddles with the Stefan-Boltzmann law and other principles.

Gleaning information from a few optical photons originating from astronomical sources; telescope's benefits include increased light-gathering power, greater sensitivity of telescopic cameras and sensors and enhanced spectral resolution.

Non-visible wavelengths compose by far the largest part of the electromagnetic spectrum; astronomers assume there is nothing to see in these bands; the invention of the radio and X-ray telescopes; the challenges of focusing radio and X-ray light.

Starting with the spectrum of sunlight; noticing that thin, dark lines are present at certain wavelengths; these lines reveal the temperature of the sun's outer atmosphere; more diffuse phenomena produce bright emission lines against a dark spectrum.

The range of stellar luminosities, temperatures, masses and radii using spectra and other data; constructing the celebrated Hertzsprung-Russell diagram, with its main sequence of stars in the prime of life; two out of three stars have companions.

Professor Winn's specialty includes extrasolar planets, also known as exoplanets; the extreme difficulty of observing an Earth-like planet orbiting a Sun-like star in a stellar neighborhood; reviewing the characteristics of many exoplanets.

Examining the sun and the mass it consumes through nuclear fusion during its 4.5-billion-year history; one pictures the sun like a giant furnace of nuclear bombs going off non-stop; calculations show it is more like a collection of toasters.

Learning how stars work by delving into the stellar structure, using the sun as a model; relying on physical principles and order-of-magnitude calculations; determining the time it takes for the energy generated in the interior to reach the surface.

The fate of solar mass stars after they exhaust their nuclear fuel; venturing into the quantum theory to understand what keeps these exotic stars from collapsing into black holes; the Chandrasekhar limit determines a white dwarf's maximum mass.

Tracing stellar evolution from two points of view; diving into a protostar and witnessing events unfold as the star begins to contract and fuse hydrogen; seeing how stellar evolution looks to observers studying stars with telescopes.

A star that weighs several solar masses to chart its demise after fusing all nuclear fuel; such stars end in a gigantic explosion called a supernova and produce a super-compact neutron star; the rapid spin of neutron stars and the energy they send.

The physics of gravitational waves, a phenomenon predicted by Einstein; it takes colliding black holes to generate gravitational waves that can be picked up by an experiment called LIGO on Earth; LIGO scientists win the 2017 Nobel Prize in Physics.

The Milky Way and locating Earth's position; surveying other galaxies; using the virial theorem to analyze a typical galaxy; galaxies themselves often collide with each other; the nearby Andromeda Galaxy is destined to collide with the Milky Way.

Examining active galaxies that have supermassive black holes gobbling up nearby stars; clusters of galaxies and the clues they give for dark matter; the distribution of dark matter; the Big Bang; evidence that most galaxies are speeding away.

The Big Bang theory is one pillar of modern cosmology; another is the cosmic microwave background radiation; the third pillar is the cosmic abundances of the lightest elements, which tell the story of the earliest moment of nucleosynthesis.

The trail of the greatest unsolved problem in astrophysics; the past, present and future of the universe; dark energy causes the expansion of the universe to accelerate; this mysterious force is traced to the lambda term in the Friedmann equation.