Astronomy

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.

The starry sky differs with the seasons, primarily because the Earth revolves around the sun, which moves slowly across the night sky. At night, only the stars facing away from the sun are visible. The rising time of stars is slightly earlier each day ...

Different civilizations initially had their own ways of dividing the sky. The modern 88 constellations were determined by the International Astronomical Union to unify astronomical research, define the boundaries of the entire sky, and standardize ...

After astronomers classified stars by magnitude, they counted more than 6,000 stars visible to the naked eye throughout the sky, but only about half of them are actually visible from the ground. Severe light pollution in cities will significantly ...

The twinkling of stars is caused by uneven heating and cooling of Earth's atmosphere and the turbulence of air currents, which refract starlight and cause changes in brightness. Planets, as surface light sources, do not twinkle, and observatories are ...

Astronomers study various celestial bodies and cosmic issues outside the Earth's atmosphere and are not responsible for weather forecasting; meteorology is an independent discipline. Only observational astronomers pay attention to the weather due to ...

Ancient people believed that the sky was spherical, but this was actually an illusion caused by the lack of human distance perception. Astronomy borrowed this concept of a celestial sphere and combined it with various coordinate systems, celestial ...