Even the nearest stars are so distant that a single diffraction limited telescope capable of imaging Earth-size planets orbiting them would be hopelessly large (see Problem 45). Astronomers get around this limitation using interferometry to combine data from several telescopes, producing an instrument that acts like a single telescope with aperture equal to the distance between the individual telescopes (Fig. ?32.30). The technological challenge is to combine the signals with their relative phase intact; for this reason, interferometry has been used successfully for decades in radio astronomy but only recently with optical telescopes.

Data From Problem 45

NASA asks you to assess the feasibility of a single-mirror spacebased optical telescope that could resolve an Earth-size planet 5 light-years away. What do you conclude?

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If a point source is located on a line at 45? to the line joining the two telescopes (source 2 in Fig. 32.30), electromagnetic waves reaching the two will bea. in phase.b. out of phase by 45?.c. out of phase by 90?.d. you can?t tell without further information

Transcribed Image Text:

* To source 1 To source 2 90°(45° FIGURE 32.30 A two-dish interfer- ometer used for radio astronomy (Passage Problems 71-74). Dashed lines show directions to sources in Problems 73 and 74. --