Astronomy

This article focuses on "Why is the bigger the astronomical telescope better", explaining that the larger the aperture of an optical telescope, the more faint and weak light it collects, and its ability is 2 million times that of the human eye; at the same time, according to the laws of optics, the larger the aperture, the ability to distinguish celestial details. The stronger it answers the two major advantages of large-aperture telescopes.

This article focuses on catadioptric telescopes. In the early 20th century, Schmidt designed catadioptric telescopes with special curvature correction lenses. The field of view was large but the lens was difficult to grind; Soviet optician Maksutov switched to a meniscus lens, which was cheaper., widely used in small telescopes. The catadioptric telescope has a large field of view suitable for sky surveys, and there are also many variants used for science popularization.

This paper explains the reasons why most contemporary large telescopes use reflective telescopes: telescopes are divided into two types: refraction and reflection. Refraction has inherent chromatic aberration. When making large apertures, light passes through glass, the requirements are high and the absorption is large. The largest refractive mirror is only 1.02 meters; Reflecting telescopes can be made with large apertures, becoming the mainstream choice for detecting faint and weak celestial bodies.

This article revolves around the controversy over the production of the first astronomical telescope: in 1608, Dutch optician Liebersch accidentally discovered that a lens combination could bring distant objects closer, and made the world's first telescope and reported it to the Dutch government, where he received an order from the Navy; neighbor Jensen claimed that it was invented early but was not announced; in 1609, Galileo improved the telescope for astronomical observations based on this.

This article introduces a variety of celestial bodies that can be observed by amateur astronomical telescopes, such as lunar craters, rings of Saturn, Milky Way constellations, Venus's profit and loss, Jupiter's stripe great red spot, Mars's polar cap, and nebulae and galaxies. It also explains the key points of lens selection, which needs to be combined with observation targets. Select focal length, weigh aperture and portability, and give priority to telescopes with high optical quality, within budget and appropriate aperture, so that the observation efficiency of dim objects can be improved through SLR.

This article introduces that before the invention of telescopes, astronomers relied on classical instruments such as the gustrum, armillary sphere (including the Yuanyou armillary sphere of the Northern Song Dynasty), and Tycho Wall Quadrant. These instruments can measure time and determine celestial coordinates. Among them, the Water Transport Instrument Observatory pioneered the active roof of an observatory and helped Kepler derive the laws of planetary motion.

This article explains that the latitude at which the observer is located determines the rising and falling laws of stars: stars near the north celestial pole at 40° north latitude in the northern hemisphere (such as Beijing) never fall, and stars near the south celestial pole never rise; no visible stars in the north pole fall, stars in the southern hemisphere do not rise, and there is no such phenomenon at the equator. The star trajectory map can visually present this law.

This article discusses the "length of a day" and introduces the difference between "solar day" and "sidereal day" defined by astronomers: the solar day is about 24 hours, and the sidereal day is about 23 hours and 56 minutes. The former includes the comprehensive effect of the Earth's revolution and rotation, and the latter only includes rotation. It was also mentioned that atomic clocks found that there were small seasonal changes in the earth's rotation that were invisible to humans.

This paper explains the cause of the change in the length of day and night: the earth's rotation has an angle of about 23.5° between the equatorial plane and the orbiting ecliptic plane. During the revolution, the direct point of the sun moves, resulting in differences in the length of day and night in the four seasons in the northern and southern hemispheres; the equatorial day and night are equal throughout the year, and the poles have half a year of polar day and polar night, with obvious changes in mid-high latitudes (such as Hainan Island, Mohe and other places)

This article explains Du Fu's poem "We never see each other in life, but we move like participating in the Shang Dynasty":"Shen" corresponds to the starry sky on winter nights (Orion), and "Shang" corresponds to Antares (fire), which is starry sky on summer nights. The two rise and fall and never meet each other. Du Fu uses this to express his emotion that relatives and friends were separated and the sky was separated during the Anshi Rebellion.

This paper discusses the rationality of "lying down and looking at the morning glory and vega" in Du Mu's "Autumn Xi", compares the same poem and different texts "sitting and watching", and combines the astronomical background of the summer triangle above the head in the Central Plains region at the turn of summer and autumn. It explains that when the summer heat has not subsided, people take the cool outdoors and watch it lying down is more suitable for the situation. It also introduces the astronomical knowledge of the cowherd and the summer triangle.

This paper expounds that star catalogs are indexes for astronomers to record the positions of celestial bodies, combs the development of important star catalogs in early and modern times at home and abroad, and explains that star catalogs are an important foundation for astronomical research. Nowadays, star catalogs are rich in types and diverse in content. They can be easily queried through the CDS database to assist in the exploration of the universe.