Today in 1787 the German astronomer Josef Farnhofer was born. It is considered the road level of modern astronomy. His field in particular was spectroscopy.
After serving as an apprentice for a lens and sight manufacturer, Fernhofer specialized in the manufacture of optical instruments. While he was designing the colorless focusing lens for the telescope, he watched the sunlight come out through such glass and it turns out that in addition to the colors of the rainbow he also saw many black lines. Fernhofer knew that some of these lines could be used as a standard for wavelengths. For this reason he began to measure their position relative to each other. He marked the most prominent lines with letters that we use to this very day.
His skills in optics, mathematics, and physics led Fernhofer to design and build instruments for measuring the refraction of light that could measure the wavelengths of specific colors and the dark lines in the Sun's spectrum. However, the telescope he built was unable to meet this task. Nevertheless, the transparent lenses are what are used today - mainly in binoculars.
Tonight is also an excellent opportunity to look for the lunar crater named after Fernhofer. Courted again to the Fornerius Crater which now looks shallow. Can you see the ring at its southern end? This is Fernhauper Crater. A challenge in today's moonlight conditions.
Now watch the twins again - Castor and Pollux. They are separated by no more than 3 arcseconds. Castor A, which has a light intensity of 2.0, has a twin - Castor B, which has a light intensity of 2.8. This pair is indeed a true double star and the orbital period of its members is about 500 years. The Castor system includes four other fainter members, each of which is a scaroscopic double star. Without Fernhofer's discovery we would never have known this.
Although spectroscopes and telescopes are powerful instruments capable of revealing a lot, sometimes it is necessary to get closer to learn more details. Today in 1986, the first of a week-long series of approaches by the Russian Vega-1 spacecraft and the European Giotto spacecraft to the orbits of Halley's Comet began.
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