filar micrometer การใช้

• Great refractors were often used for observing double stars and equipped with a Filar micrometer.
• Filar micrometers are little used in modern astronomy, having been replaced by digital photographic techniques where digital pixels provide a precise reference for image distance.
• Being very difficult to measure, only about 60 stellar parallaxes had been obtained by the end of the 19th century, mostly by use of the filar micrometer.
• A typical filar micrometer consists of a micrometer and a reticle that has two fine parallel wires or threads that can be moved by the observer using a micrometer screw mechanism.
• The first successful measurements of stellar parallax ( to determine the distance to a star ) were made by Friedrich Bessel in 1838 for the star atmospheric turbulence in measurements compared to a filar micrometer.
• A "'filar micrometer "'is a specialized eyepiece used in astronomical telescopes for astrometry measurements, in microscopes for specimen measurements, and in alignment and surveying telescopes for measuring angles and distances on nearby objects.