Astronomy Chapters 23–24: Light, the Sun, Stars, and Galaxies

What is cosmology?

The study of the universe, including its properties, structure, and evolution.

Who proposed that fuzzy patches in the sky were distant galaxies?

Immanuel Kant in the 1700s.

What did Edwin Hubble study to solve the mystery of Kant's fuzzy patches?

Cepheid variables, which are pulsating variably bright stars.

What is the relationship between the period of variability and luminosity in Cepheid variables?

Larger, brighter Cepheids have longer pulsation periods.

What is the Big Bang theory?

The model that describes the birth and current state of the universe, originating from a cataclysmic explosion 13.7 billion years ago.

What is the radius of the visible universe estimated to be?

Approximately 46.6 billion light years.

What is stellar parallax?

The apparent shift in a star's position due to the orbital motion of Earth, measured as an angle.

What is a light-year?

The distance that light travels in one year, approximately 9.5 trillion kilometers (5.8 trillion miles).

What is absolute magnitude?

The intrinsic brightness of a star at a standard distance of 32.6 light-years (10 parsecs).

What factors control a star's brightness?

Size, temperature, and distance.

What is the temperature range for hot stars?

Above 30,000 K, emitting short-wavelength light and appearing blue.

What are binary stars?

Two stars orbiting one another, held together by mutual gravitation.

What does the Hertzsprung-Russell Diagram show?

The relationship between stellar brightness (absolute magnitude) and temperature.

What are the two types of variable stars?

Pulsating variables, which fluctuate regularly in brightness, and eruptive variables, which experience sudden brightening.

What is a nebula?

A cloud of dust and gases in space.

What are the two major types of nebulae?

Bright nebulae, which glow if close to a hot star, and dark nebulae, which appear dark and contain cool gas.

What is a protostar?

A stage in stellar evolution where gravitational contraction continues and the core reaches 10 million K, allowing hydrogen nuclei to fuse into helium.

What happens during the red giant stage of a star?

Hydrogen burning migrates outward, the star's outer envelope expands, and the surface cools and becomes red.

What are the final stages of stellar evolution for low-mass stars?

They become white dwarfs after not being hot enough to reach the red giant stage.

What occurs during a supernova?

A massive star terminates in a brilliant explosion, potentially producing a neutron star or a black hole.

What did Edwin Hubble study to understand the universe?

Cepheid variables, which are pulsating variably bright stars.

What is the Hertzsprung-Russell Diagram?

A graph showing the relationship between stellar brightness (absolute magnitude) and temperature.

What is the process called when hydrogen nuclei fuse to become helium nuclei?

Hydrogen burning.

What happens during the red giant stage of a star's evolution?

The star's outer envelope expands, surface cools, and it becomes red as the core collapses.

What is a supernova?

A brilliant explosion that occurs when a massive star runs out of nuclear fuel and collapses under its own gravity.

What distinguishes Type I and Type II supernovae?

Type I occurs when a star accumulates matter from a neighbor, while Type II occurs when a star collapses under its own gravity.

What is a white dwarf?

A small, dense stellar remnant that can be more massive than the Sun, with a spoonful weighing several tons.

What happens to a white dwarf as it cools?

It eventually becomes a black dwarf.

What is a neutron star?

A stellar remnant formed from a more massive star after a supernova, with a density similar to an atomic nucleus.

What is a pulsar?

A type of neutron star that emits pulsating radio waves, first discovered in the early 1970s.

What defines a black hole?

An object with more density than a neutron star, with intense gravity that prevents light from escaping.

What is the Milky Way galaxy?

A large barred-spiral galaxy about 100,000 light-years wide, containing three spiral arms of stars.

How far is the Sun from the center of the Milky Way galaxy?

About 30,000 light-years.

What are the four basic types of galaxies?

Spiral, barred spiral, elliptical, and irregular galaxies.

What characterizes a spiral galaxy?

Arms extending from the nucleus, containing both young and old stars.

What is Hubble's Law?

The recessional speed of galaxies is proportional to their distance from us.

What does a redshift indicate?

That a galaxy is moving away from us, stretching the wavelength of light and making it appear redder.

What are the three possible fates of the universe according to current theories?

1) The universe lasts forever, 2) Outward expansion stops and gravitational contraction follows, 3) Outward expansion accelerates, ripping space and time apart.

What is a galactic cluster?

A group of galaxies that can contain thousands of galaxies.

What is the Local Group?

Our own group of galaxies, which contains at least 28 galaxies.

What is a supercluster?

A huge swarm of galaxies, potentially the largest entity in the universe.

What is degenerate matter?

Matter in which electrons are displaced inward, found in white dwarfs.

What is the significance of the Crab Nebula?

It is the remnant of a supernova from A.D. 1054 and contains a pulsar.

What is the density of a neutron star compared to a white dwarf?

A neutron star is much denser than a white dwarf, with a pea-sized sample weighing about 100 million tons.

What is the role of gravity in the formation of a neutron star?

Gravity from a massive star collapses atoms, leading to the formation of neutrons.

What is electromagnetic radiation?

A form of energy that includes gamma rays, X-rays, ultraviolet light, visible light, infrared light, and radio waves.

What is the speed of light in a vacuum?

300,000 kilometers (186,000 miles) per second.

What are the two models used to describe light?

The wave model and the particle model.

What is spectroscopy?

The study of the properties of light that depend on wavelength and its interaction with matter.

What is a spectrum?

The light pattern produced by passing light through a prism, spreading out various wavelengths.

What is a continuous spectrum?

A spectrum produced by an incandescent solid, liquid, or gas under high pressure, showing an uninterrupted band of color.

What is a dark-line (absorption) spectrum?

A spectrum produced when white light passes through a cool, low-pressure gas, appearing as a continuous spectrum with dark lines.

What is a bright-line (emission) spectrum?

A spectrum produced by a hot gas under low pressure, appearing as a series of bright lines of specific wavelengths.

What is the Doppler effect?

The apparent change in wavelength of radiation caused by the relative motions of the source and observer.

What are the two basic types of optical telescopes?

Refracting telescopes and reflecting telescopes.

How does a refracting telescope work?

It uses a lens to bend (refract) light to produce an image.

What is chromatic aberration?

An optical defect in refracting telescopes that causes color distortion.

What is the advantage of reflecting telescopes over refracting telescopes?

Reflecting telescopes do not suffer from color distortion.

What is the light-gathering power of a telescope?

The ability of a telescope to intercept light, determining the brightness of the image.

What is the resolving power of a telescope?

The ability to separate close objects, allowing for sharper images and finer detail.

What is the magnifying power of a telescope?

The ability to make an image larger, calculated by dividing the focal length of the objective by the focal length of the eyepiece.

What is the solar interior composed of?

The core, radiation zone, and convective zone.

What is the photosphere?

The Sun's 'surface', a layer of incandescent gas less than 500 kilometers thick.

What are sunspots?

Dark areas on the solar surface with a cooler temperature, following an 11-year cycle.

What are prominences in solar features?

Huge arching cloudlike structures extending into the corona, consisting of concentrations of chromospheric gases.

What are solar flares?

Explosive events that release enormous quantities of energy and can cause auroras on Earth.

What is the nuclear fusion process in the Sun?

The proton-proton reaction where four hydrogen nuclei are converted into a helium nucleus, producing energy.

How much hydrogen does the Sun consume each second?

600 million tons.

How long can the Sun continue to produce energy?

For another five billion years.

What is the temperature of the Sun's core?

Approximately 15 million K.

What is the temperature of the Sun's photosphere?

Approximately 6000 K (10,000˚F).

What is the corona?

The outermost portion of the solar atmosphere, very tenuous, with temperatures exceeding 1 million K.