Stars And the HR Diagram

Explore stars and the HR Diagram! Master stellar life cycles and classification.

Correctly fill in the blanks. Stars are spherical, luminous masses of gasses, mainly hydrogen. They produce energy by nuclear fusion. Fusion occurs in a star's very hot core where hydrogen protons combine to form helium. This nuclear reaction releases light and heat energy.A star forms within a cloud of gas and dust called a nebula. The mass of dust and gas in the nebula begin to contract because of the force of gravity. This makes the nebula denser and hotter. The nebula will first become a protostar. Then the center of the protostar is dense and hot enough for fusion of hydrogen, a star is "born". The star will spend most of its life as a main sequence star. After millions to billions of years, the star will expand to become a red giant or supergiant. A very massive giant star will eventually supernova (explode) and then become an object so dense that no light can escape called a black hole. A low mass red dwarf star turn into a red giant , and then will collapse to form a white dwarf which is extremely hot and dense. Hotter starts will go through the life cycle more quickly because they use their hydrogen "fuel" faster. Stars are classified based on temperature and luminosity. The HR diagram illustrates the classification system for stars. Ninety percent of stars are main sequence stars. Main sequence stars increase in luminosity as their size and temperature increases. Red dwarfs are small, cool, and dim. The cool red supergiants and giants are bright because of their huge size. The very hot white dwarfs are dim because of their very small size. Determine which statements are true and which are false. True Stars are classified by temperature and luminosity Stars spend the majority of their life as main sequence stars. The Sun is an average, main sequence star. The mass of a star determines its life cycle. The Sun will become a red giant then a white dwarf. False The Sun is a supergiant. Blue stars are coolest and red stars are hottest. The color of a star determines its life cycle. All stars become blackholes Polaris is a white dwarf. The Sun will become a blackhole. Use this HR diagram to answer the questions below. Which color indicates the hottest star surface temperature? blue white yellow red Compared with our Sun, the star Betelgeuse is smaller, hotter and less luminous smaller, cooler and more luminous larger, hotter and less luminous larger, cooler and more luminous Which star is hotter and many times brighter than Earth's Sun? Barnard's Star Betelgeuse Rigel Pollux Which two stars have the most similar luminosity and temperature? Betelgeuse and Barnard's Star Rigel and Betelgeuse Alpha Centauri and the Sun Sirius and Procyon B Compared to the temperature and luminosity of the star Polaris, the star Sirius is hotter and more luminous hotter and less luminous cooler and more luminous cooler and less luminous In nuclear fusion what occurs? Lighter elements are converted to heavier elements Lighter elements are converted to even lighter elements Heavier elements are converted to lighter elements Heavier elements chemically combine with lighter elements Compared to the surface temperature and luminosity of massive stars in the Main Sequence, the smaller stars in the main sequence are hotter and less luminous hotter and more luminous cooler and less luminous cooler and more luminous The temperature of Spica is closest to 2,500 K 3,200 K 4, 000 K 25, 000 k Bellatrix has a surface temperature of 21, 000 K. What is its color? Red Yellow White Blue What is the relationship between Temperature and Luminosity of Main Sequence stars? As temperature increases, luminosity increases. As temperature increases, luminosity decreases. As temperature increases, luminosity stays the same. Label HR Diagram Label the 4 categories on the HR Diagram. White dwarfs Main Sequence Giants Supergiant