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maya Astronomy Chapter 8

maya Astronomy Chapter 8 - Astronomy Chapter 8...

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Astronomy Chapter 8: Characterizing Stars stellar parallax - apparent motions of nearby stars compared to background, distant stars because of the Earth’s motion around the Sun; used to measure distances to nearby stars - First stellar parallax measurement was made in 1838 by Bessel. - Bessel chose 61 Cygni because it had the highest ‘proper motion’ of any known star. - Earth-based telescopes are limited to parallax measurements of 0.01 arsec - Hipparcos space telescope measured stellar parallaxes from 1989-1993 for 120,000 stars. Angular Measurements - The sky is divided into 360 degrees. - Each degree has 60 arcmin. - Each arcmin has 60 arcsec. - In our galaxy, a parsec is a measure of distance, not of time. apparent magnitude – how bright a star appears to us here on Earth; depends on how much light the star emits and how far away it is - Apparent brightness decreases inversely with the square of the distance between the source and the observer. - For two identical stars: if one is twice as far away, it is ¼ as bright. absolute magnitude – how bright a star would appear from a distance of 10 parsec - tells us whether a star is intrinsically bright or intrinsically faint - brightest star = -10 - faintest star = +20 luminosity – total energy emitted every second -
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