Pearson Prentice Hall Physical Science Concepts in Action

Pearson Prentice Hall Physical Science: Concepts in Action Chapter 26 Exploring the Universe Chapter 26. 2 THE STARS

Measuring Distance • Def: a star is a large, glowing ball of gas in space which generates energy through nuclear fusion in its core • Def: a light-year is the unit of distance that light travels in a vacuum in one year

PARALLAX • Def: parallax is the apparent change in position of an object with respect to a distant background – – – Scientists use parallax to measure distances Hold your thumb at arm’s length in front of you and cover one eye Keep your thumb in the same spot & cover the other eye The apparent movement of your thumb is the parallax effect Astronomers measure the parallax of nearby stars to determine their distance from Earth https: //3. bp. blogspot. com/-5 adnzr 3 u. Mo. Q/Ur 4 ZEmb 5 x. DI/AAAAVC 0/Xbx. XMf. FHQd. I/s 1600/parallaxthumb. jpg http: //www. schoolsobservatory. org. uk/sites/default/files/astro/paraerth. jpg

Chemical and Physical Properties • Astronomers classify stars by: – – color, size, and brightness luminosity chemical composition and mass temperature • A star’s color indicates the temperature of its surface – The hottest stars are blue (30, 000 K) & – cool stars are red (3, 000 K) – Yellow stars (like our sun) are intermediate temperature (5, 000 -6, 000 K)

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SPECTROSCOPY • Scientists get more precise information about a star by using color spectra & atomic absorption spectra (to indicate the presence of certain elements) https: //media 1. britannica. com/eb-media/02/96902 -004 -856 CCB 82. jpg

ABSORPTION LINES • Def: absorption lines are a set of dark lines that show where light has been absorbed in the atomic absorption spectra – Each star has its own atomic absorption spectrum which indicates which elements are present in the photosphere • Most stars have a chemical makeup that is similar to the sun • It is mostly hydrogen and helium making up nearly 99% of the star’s mass

APPARENT BRIGHTNESS • Def: apparent brightness is the brightness of a star as it appears from Earth • Brightness is affected by distance from Earth http: //www. star. ucl. ac. uk/~msw/teaching/PHAS 2 521/ism_dust_files/bright_dist. gif

ABSOLUTE BRIGHTNESS (luminosity) • Def: absolute brightness is how bright a light REALLY is • Absolute brightness does not depend on distance & it is calculated using distance in the calculation

How to Produce Energy • It wasn’t until the 1960 s that scientists discovered that the sun produces its energy in its core central region • The process is nuclear fusion – Recall that nuclear fusion has not happened on Earth yet because of the high temperatures required – The temperatures required for nuclear fusion exist on the sun http: //www. cfht. hawaii. edu/Instruments/Spectroscopy/Es padons/www. ast. obsmip. fr/users/donati/press/images/sun. jpg http: //resources. gale. com/gettingto greenr/files/2014/03/fusion_diagra m. jpg

MASS AND BRIGHTNESS • Astronomers: – can use information about temperature and brightness to estimate diameter (width) and calculate volume of a star – calculate mass indirectly by observing the gravitational interaction of stars that occur in pairs • There appears to be a relationship between absolute brightness and mass