Stars, Galaxies, and the Universe Section 1

Tools of Modern Astronomy Constellations: Patterns of stars in the sky.

Electromagnetic Radiation Visible light: Light you see with your eyes. Electromagnetic radiation: Energy that can travel directly through space in the form of waves.

Electromagnetic Spectrum Wavelength: The distance between the crest of one wave and the crest of the next wave. Spectrum: light that spreads out to make a range of different colors with different wavelengths. Electromagnetic spectrum: includes radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

Telescopes Telescopes: Collect and focus different types of electromagnetic radiation including visible light. Convex lens: A piece of transparent glass, curved so that the middle is thicker than the edges. Refracting telescopes: use convex lens to gather a large amount of light and focus it into a small area. Reflecting telescopes: Uses a mirror instead of a lens. Radio Telescopes: Detect radio waves from objects in space. Observatory: A building that contains one or more telescopes.

Spectrographs Spectrograph: Breaks the light from an object into colors and photographs the resulting spectrum. Astronomers use spectrographs to get information about stars, including their chemical compositions and temperatures.

Chemical Composition and Temperature of Stars Chemical elements in a star’s atmosphere absorb light from the star. Each element absorbs light at different wavelengths. Thus by comparing them to other known spectrums of different elements astronomers can infer which elements are found in a star. Chemical composition of stars are about 73% hydrogen,25% helium, and 2% other elements. By comparing a star’s spectrum with the known spectrums of elements at different temperatures, astronomers can infer how hot the star is.

Review For what purpose are telescopes designed? Telescopes collect and focus electromagnet radiation. What can astronomers tell from looking at a star’s spectrum? Astronomers can determine the chemical composition and the temperature of the star.

Section 2 Characteristics of Stars

Terms Characteristics of Stars Galaxy: Contains hundreds of billions of stars. (Milky Way) Universe: All of space and everything in it. Light-year: Distance that light travels in one year. It is a unit of distance not time. Parallax: The apparent change in position of an object when you look at it from different places.

Classifying Stars The main characteristics used to classify stars are: Size, Temperature and Brightness. Star sizes largest to smallest are: Super Giant, Giant, Medium, White Dwarf, and Neutron stars.

Color and Temperature of Stars A stars color reveals its temperature. The coolest stars are red and hottest stars are blue, blue-white. The brightness of a star depends upon its size and temperature. How bright a star looks from Earth depends on both how far the star is from Earth and how bright the star actually is.

Brightness Apparent magnitude: Is the star’s brightness as seen from Earth. (use electronic devices to measure it. Absolute magnitude: A brightness a star would have if it were a standard distance from Earth.

Hertzsprung-Russell Diagram A graph used by astronomers that shows the relationship between surface temperature and brightness of stars. Most stars (90%) fall under the Main Sequence in which surface temperatures increases as brightness increases.

Review What is a parallax? How is it useful in astronomy? Parallax is the apparent change in an object’s position when viewed from two different places. Astronomers can use parallax to calculate distances to nearby stars. List three characteristics used to classify stars. Size, temperature (or color) and brightness Which is hotter-- a red star or a blue star? Why? Blue stars are hotter than red stars because gas glows red at lower temperatures and blue at higher temperatures.

Section 3 Lives of Stars

A Star Is Born Nebula: All stars start out as nebulas. A large amount of gas and dust spread out in an immense volume. Proto: Greek for “earliest” Protostar: Earliest stage of a star. A star is born when the contrasting gas and dust become so hot that nuclear fusion starts. How long a star lives depends on how much mass it has. (More mass=shorter lives)

Death of Stars When a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole. When it runs out of fuel the center of the star shrinks and the outer part of the star expands.

Terms of Stars White dwarf: The remaining hot core of a star after its outer layers have expanded and drifted out into space. Neutron Star: A tiny star that remains after a supernova explosion. Supernova: The explosion of a dying giant or supergiant star. Black hole: The remains of an extremely massive star pulled into a small volume by the force of gravity.

Review What is the earliest stage in the life of a star? The star begins as part of a nebula. A cloud of dust and gas. Some of the dust and gas condenses to form a protostar. Nuclear fusion begins and the protostar becomes a star. Why do small-mass stars have longer lifetimes than large-mass stars? Small-mass stars burn their fuel more slowly than large-mass stars.

Review continued What is the difference between stars that become white dwarfs and stars that become neutron stars? Giant stars collapse into neutron stars. Smaller stars form white dwarfs. What evidence do astronomers use to detect black holes? Scientist detect black holes by observing radiation from hot gas near the black hole, and by studying the effect of the black hole’s gravity on a nearby star.

Section 4 Star Systems and Galaxies

Star Systems and Planets Our solar system has only one star, the sun. More than half of all stars are members of groups of two or more stars, called star systems. Binary Stars: Star systems with two stars are called double stars or binary stars. Eclipsing Binary: A System in which one star blocks the light from another.

Review What was the Big Bang? A giant explosion in which all the matter in the universe began moving apart. Describe how the solar system formed. The solar system formed out of a collapsing, spinning disk of gas and dust. The center of the disk formed the sun. Matter toward the edge formed the planets, asteroids, and a cloud of ice and other substances. What observations show that the universe is expanding? The galaxies are all moving away from each other. The farther away a galaxy is away from the Milky Way, the faster it moves away, because there is more space.

Galaxies 3 Main Galaxies: Spiral Galaxies, Elliptical Galaxies Irregular Galaxies Spiral: A galaxy that has the shape of twin spirals. Elliptical: Look like flatten balls. Irregular: Do not have a regular shape.

Review What is a star system? A star system is a group of two or more stars. Describe the 3 main types of galaxies. Spiral galaxies are shaped like twin spirals, with arms that spiral out like pinwheels. Elliptical galaxies look like flattened balls. Irregular galaxies do not have regular shapes. Where is the sun in our galaxy? The sun is about 25,000 light-years away from the center of the galaxy, about 2/3 of the way out in one of the spiral arms.

Section 5 History of the Universe The galaxies in the universe are like the raisins in rising bread. The raisins move away from each other as the bread rises. The universe is getting bigger all the time.

Big Bang Theory The initial explosion that resulted in the formation and expansion of the universe. The universe was small, hot, and dense. It exploded about 10 to 15 billion years ago to make our universe.

Formation of the Solar System After the big bang, matter in the universe separated into galaxies. Gas and dust spread throughout space in our galaxy. About 5 billion years ago, a giant cloud of gas and dust, or nebula, collapsed to form the solar system. Nebula shrank to form a disk = the sun was born. The spheres closest to the sun lost most of their gases and became the inner planets. The spheres farthest from the sun became the gas giants or the outer planets.