Parallax
Transcript: * Depth perception * The brain utilizes parallax to perceive depth through a process known as stereopsis * In this case, the baseline consists of the distance between the eyes which is typically 6 cm * Allows us to see up to tens of feet *Babies have a well developed sense of depth by 18 months *Pidgions have to bob their heads in order to perceive depth Race to the stars ᶿᶿ * Today's excepted value is 0.287 arcseconds Parallax Given the time it would take for each measurement, finding the perfect candidate was vital Friedrick Wilhelm Struve 1793 – 1864 The Race was on Thomas Henderson 1798-1844 By the 18th century, astronomers had a better understanding of the motion of stars and began to look for candidates based on how fast they appeared * Today's accepted value 25.05 light years Before the 18th century astronomers believed the stars shared the same properties so they based the distance to the stars on brightness * Measured the parallax of 61 Cygni Parallax now and why it is important * He found the parallax to be 0.2613 arcsconds-roughtly 26 light years Stellar * Measured the parallax of Vega Friedrick Wilhelm Bessell 1784 – 1846 d = 1/p * Bessel was the first to publish his findings *Who actually won the race to the stars is a toss up because Henderson chose not to publish his findings sooner because he did not have confidence in his measurements * Parallax solidifies the heliocentric theory Parallax [par-uh-laks] noun the apparent displacement of an observed object due to a change in the position of the observer. Origin: 1585–95; < Greek parállaxis change, equivalent to parallak- (stem of parallássein to cause to alternate, equivalent to para- para-1 + allássein to vary, akin to állos other; see else, allo-) + -sis -sis *Today parallax is also measured by satellites and by photography and digital imaging techniques BEFORE WE REACH FOR THE STARS!!! * Fixed objects closer to the observer have greater parallax than objects farther away Hirshfeld, Alan. Parallax : the race to measure the cosmos. New York: Henry Holt, 2002. Print. Components of a parallex That is, assuming stars travel about the same speed and in the same direction, stars that are closer to earth would appear to have a larger proper motion than their counterparts farther away * Measured the parallax of the star system Alpha Centauri * He found the systems parallax to be a little more than one arcsecond, putting it at a distance of 200,000 astronomical units Photometric Technique * Two lines of sight (2 locations) that create a BASELINE 2 Work Cited 1 parsec=206,265 AU 1 parsec=3.0857X1016 m 1 parsec=3.2616 light years d *Henderson, Bessel, and Struve worked independently from one another using different instruments 1 Au Parallax and Distance Measurement http://lcogt.net/spacebook/parallax-and-distance-measurement Because stars and the earth are so far apart, identifying parallax was no easy task Stellar Parallax ---------------- * Understanding the distance to the stars along with other properties allows us to deduce the masses, temperatures, life cycles and nature of stars * Baseline = 2 astronomical units (186 million miles) * Parallax is used to find the distance between the sun and the stars *Distance d and Parallax p take the form d = 1/p where d is measured in parcsecs and p in arcseconds * Today's excepted value is 0.72 arcseconds Guillot, B.J. Distance: A History of Parallax and Brief Introduction to Standard Candles. Houston, TX * With hundreds of positions and thousands of measurements, he found the parallax angle to be 0.348 arcseconds from earth
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