Unformatted text preview: in the 18th century using the transits of Venus, rare events where Venus crosses the Sun. Viewed from different parts of the Earth Venus crosses the Sun at different latitudes of the Sun. By sending observers such as Captain Cook on his first Pacific voyage astronomers were able to measure the Astronomical Unit. 3. Now we can use our knowledge of the Astronomical Unit to measure the parallax to nearby stars. If we measure positions of stars on the sky at two opposite points of the year (let's say, summer and winter) we do so from two positions in space that are 2 x AU away from each other. A nearby star will appear to shift positions relative to more distant stars in the background. If we measure the shift in position as an angle in arcseconds (all stars have a parallax of less than 1 arcsecond as seen from Earth) then the distance in parsec is 1/angle. Thus a star with a parallax angle of 0.1 arcseconds is 10 parsecs away from us....
View Full Document
- Spring '08