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STUDY GUIDE FOR CHAP. 4.2 – CHARACTERISTICS OF STARS I. CLASSIFYING STARS - All stars are huge spheres of glowing ___. - They are made up mainly of ________ and produce __________ through nuclear fusion. - The nuclear energy released from the nuclear fusion is ___________ into electromagnetic radiation. - This conversion of energy makes stars shine ____________. - Astronomers classify stars according to their physical characteristics of _______, ___________, _______, ___________, and ____________. A. COLOR AND TEMPERATURE - The stars’ colors reveal the ____________________ of the stars. - Cool stars appear _________ in color with a surface temperature of about 3,200 degrees Celsius. - Warm stars appear _____________ in color with a surface temperature of about 5,500 degrees Celsius. - The hottest stars are ____________ in color and have a surface temperature over 20,000 degrees Celsius. B. SIZE - Very large stars are called _________ or ______________. These stars are 10X – 100X larger than the Sun. - Stars like the Sun are considered ______________ stars. - Stars that are the size of Earth are called _____________ Stars. - The smallest known stars are called ____________ Stars and are only 20 kilometers in diameter. C. CHEMICAL COMPOSITION - The chemical composition of most stars is _____% hydrogen, ______% helium, and ___% other elements. This is very close to our Sun’s chemical composition. - Astronomers use a ______________ to determine the elements found in stars. - A spectrograph is a device that breaks ________ into colors and produces a color-banded image of the resulting colors. - The color-banded image is similar to our ___________ – it is a star’s id. It shows what chemicals are present. - The black band within the color is a wavelength of that color ___________by a star’s atmosphere. 1 II. BRIGHTNESS OF STARS - The brightness of a star depends upon both its _________ and ____________. - If a star is very hot or very big, it will be very __________. - On Earth, the brightness of a star depends upon its _______ from Earth (apparent brightness) and how ______ the star truly is (absolute brightness). A. APPARENT BRIGHTNESS - Stars that are _________ to Earth appear brighter to us and stars ____________ from Earth seem dimmer. B. ABSOLUTE BRIGHTNESS - Def. of absolute brightness: the true _____________ a star would have if all stars were the same standard distance from Earth. III. MEASURING DISTANCES TO STARS A. THE LIGHT-YEAR - Astronomers use a unit called the ___________ to measure distances between the stars. - A light-year is the distance that light travels in _________ year which is about 9.5 million kilometers. - Light travels in space at a speed of about ____________ kilometers per second. - It takes the sun’s light __ minutes to travel from the sun to Earth. B. PARALLAX - Def. of Parallax: An apparent __________ in position of an object when you look at it from different places. C. PARALLAX IN ASTRONOMY - Astromoners are able to measure the parallax of nearby stars to determine their __________. - Astronomers do this by measuring the distance of the nearby star when it is on ____ side of the sun. Then, they wait ______ months to measure it again when it is on the other side of the sun. - The _______________ between the two measurements tells astronomers how far away certain stars. IV. THE HERTZSPRUNG-RUSSELL DIAGRAM - Over 100 years ago, two scientists working independently came upon the same discovery. - Both scientists, __________________ and ____________, made graphs to find out if the surface temperature of a star and its absolute brightness were related. 2 - The two scientists concluded from their graphs that the hot ____________ stars are found on the left side of the diagram while the cooler _______stars are found on the right side of the diagram. - Also, the absolute brightest stars are located on the _____ of the diagram and the dimmest stars are located at the _________ of the diagram. - 3