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In the early 20th century, there was a debate about the existence of canals on Mars. Some astronomers argued that the canals were too narrow to be resolved by telescopes, while others believed that the eye's ability to resolve dark linear objects against a bright background was greater than the Dawes limit, which calculates the resolving power of a telescope. Experiments were conducted to determine the minimum aperture required to discern certain features, such as the Cassini Division in Saturn's rings. It was found that linear features, such as divisions in Saturn's rings and lunar rilles, could be seen with smaller apertures than predicted by the Dawes limit. Other dark linear features, such as radial striations in sunspots and festoons in Jupiter's atmosphere, also defied conventional wisdom about resolution limits. [Extracted from the article]

The article titled "A Privileged Generation: Planetary astronomers in the latter half of the 20th century lived in what Carl Sagan deemed 'a very special time'" discusses the unique experiences of planetary astronomers during the latter half of the 20th century. The author highlights the perspective of Carl Sagan, who believed that this period was particularly significant for the field. The article does not provide any further information or details about this topic. [Extracted from the article]

Due to Venus's massive, distended atmosphere, calculations suggest Venusian meteors should start to burn up at altitudes of 250 to 300 km - far above the planet's thick blanket of clouds, which extends to an altitude of 65 km. The apparent angular size of Venus varies from about 30" when its crescent is 40% sunlit to about 40" when it is 20% sunlit, so a magnification of 200× makes the planet appear about four times larger than the Moon as seen with the naked eye. PHOTO (COLOR): Venus's vast nightside presents a virtually untapped resource for observers watching for impactors burning up in the planet's dense atmosphere. [Extracted from the article]

OBSERVING In 1890, the philosopher and educator William James wrote: "Round about the accredited and orderly facts of every science there ever floats a sort of dust-cloud of exceptional observations, of occurrences minute and irregular and seldom met with, which it always proves more easy to ignore than to attend to." The history of visual planetary observing provides no better example of James's maxim than a series of controversial observations of Saturn's C ring that were unfolding about the time he penned those words. PHOTO (COLOR): During a 1992 observing run at the Pic du Midi Observatory Stephen O'Meara glimpsed delicate blotches in the C ring that were not as narrow as the ephemeral spokes in the adjacent B ring. [Extracted from the article]

On an expedition to nearby Kasprowy Wierch mountain in the late winter through early spring of 1961, Kordylewski took 11- to 13-minute photographic exposures of the L5 region using a wide-field Leica camera equipped with a 50-mm f/1.5 lens. PHOTO (COLOR): Reported to appear similar to but considerably fainter than the gegenschein seen at left, Kordylewski's clouds of dust reside 60° ahead of and behind the Moon in its orbital path. [Extracted from the article]

Reports that amateur astronomers can raise the performance of low-cost refracting telescopes a notch or two by simply adding a modern eyepiece filter. Use of achromats to block the secondary spectrum's defocused red, blue and violet light; Wratten filters with dissolved organic pigments tailored to transmit certain wavelengths and absorb others; Sophisticated filters for suppressing the secondary spectrum of achromats.

Focuses on the discovery that the four largest moons of Jupiter were low-density like Saturn's rings according to Harvard astronomer William Henry Pickering. Family background of the astronomer; Use of a Boyden Telescope at Arequipa; Description of the Galilean satellites with appearance of tiny eggs.

The article offers information on several eyepiece types that astronomers can choose from. The eyepieces that have high light transmission provide planetary details and freedom from ghost images, internal reflections, and scattered light. Information about monocentric introduced by Hugo Adolf Steinheil in 1883, the orthoscopic designed by German mathematician and physicist Ernst Abbe, and the plossi that is brainchild of Viennese optician Georg Simon Plossi, is provided.

The article focuses on the Messenger probe to Mercury launched by the U.S. National Aeronautics and Space Administration (NASA). The Messenger is known as the last spacecraft to offer the first close-up views of the surface of Mercury. Græco-Roman mythology inspired the markings names used in a chart of the planet drawn by Greek astronomer Eugène Antoniadi during the 1920s. The Mercury observations made by Walter Haas, founder of the Association of Lunar and Planetary Observers, are also mentioned.