Astronomy

This article focuses on the question of why we can't see the back side of the moon from Earth, explaining that the moon's rotation and revolution periods are the same due to tidal locking with the Earth, so it always faces the Earth with the same side. It also introduces the principle of tidal locking, the situation of tidal locking in many celestial bodies in the solar system, and the knowledge that the Earth's rotation will gradually slow down and may also be subject to tidal locking in the future.

This article focuses on the question of "Is the moon at the Mid-Autumn Festival the fullest?" It explains the definitions of "new moon" and "full moon" in the lunar calendar and the law of the full moon's timing, demonstrating that the duration of new and full moons is not fixed due to the elliptical orbit of the moon around the Earth. Based on the statistical data of new and full moons from 2005 to 2020, it points out that the full moon of the Mid-Autumn Festival often occurs on August 16 or even 17. It also mentions that the size of the full moon varies depending on the distance between the Earth and the moon, and corrects the cognitive limitations related to the sayings "The moon is especially bright at the Mid-Autumn Festival" and "The bright moon rises above the sea, and people everywhere share this moment".

This article answers the question of why there are only day and night on the moon, but no seasons. It explains that the alternation of day and night on celestial bodies results from the difference in their periods of rotation and revolution. The moon, which revolves around the Earth and the Sun with a period of one year and a period of one month for its rotation, experiences an alternation of day and night with half a month of daylight and half a month of night, accompanied by extreme temperature differences. At the same time, it shows that for celestial bodies to have seasons, they must simultaneously meet two conditions: orbiting the Sun and having a certain inclination between the plane of their rotation axis and that of their revolution orbit. Since the rotation axis of the moon is nearly perpendicular to the plane of the Earth's revolution orbit, it does not have seasons.

This article focuses on the question of "Is a year on Earth always 365 days?" and introduces the origin of the current calendar's 365-day year, the uneven and long-term slowing trend of the Earth's rotation speed, its influencing factors and geological evidence. It also explains the definitions of International Atomic Time and Coordinated Universal Time, as well as the rules for setting leap seconds.

This article conducts a popular science explanation on the topic of "Why the North Star is not equivalent to the North Celestial Pole", introducing the basic concepts of the celestial sphere, the North Celestial Pole, and the North Star. It explains that since the Earth is not a perfect sphere and is subject to the gravitational pull of the Sun and the Moon, resulting in the precession of the Earth's axis, the North Celestial Pole moves around the North Pole on the celestial sphere with a cycle of about 26,000 years, and the corresponding stars of the North Star will also change accordingly. At the same time, it explains the knowledge related to the precession of the Earth's axis that causes the precession of the equinoxes.

This article addresses the question of "why the temperature of the solar corona is actually higher than that of the Sun's surface". It introduces the anomalous phenomenon that the temperature of the solar corona is much higher than that of the Sun's surface, the structure of the transition zone between the chromospheric layer and the solar corona, and the two widely accepted theories of coronal heating: acoustic wave heating and magnetic reconnection. It also points out that there is still no perfect quantitative explanation for this problem, and more observational data and in-depth research are needed to solve it.

This article focuses on the core question of "Have the missing solar neutrinos been found?" and reviews the discovery process of the missing solar neutrino phenomenon and the research and exploration efforts of the academic community. Ultimately, the missing solar neutrino problem was resolved through the theory of neutrino oscillation and related experiments. Two leading scientists in this field were awarded the Nobel Prize in Physics for their contributions to this research.

This article focuses on the question of "Is the sun darker when there are more sunspots?" It introduces the actual scale of sunspots, points out the observation conclusion that the more sunspots there are, the brighter the sun will be, and explains that this phenomenon is due to the fact that the brightness of the flare accompanying the appearance of sunspots is enough to compensate for the weakening brightness of the sunspots and even more than that.

This article focuses on why the number of sunspots varies from year to year. It introduces that the activity of sunspots has a periodicity of about 11 years on average, and their number and distribution on the solar surface show regular changes with the activity cycle. The length of the solar activity cycle is not constant and there are overlapping longer cycles. However, the reason for the 11-year cycle of solar activity remains a mystery, and the related mechanisms still need further research.

This article explains the formation reason of sunspots, which look like "freckles" on the surface of the sun, and introduces the structural characteristics of the three layers of the sun's atmosphere from inside to outside, namely the photosphere, chromosphere, and corona, as well as the corresponding solar activity phenomena in each layer.

This article focuses on the topic of "Why do we say that the sun also has a life cycle of growth, maturity, and death?" It introduces the complete life cycle of the sun as a medium-mass star, which includes the birth from a gas cloud through contraction, the stable phase of the main sequence star, the expansion stage of the red giant star, and finally the ejection of the outer layers to form a planetary nebula, with the core evolving into a white dwarf. It also explains that the final fates of stars of different masses vary.

This article focuses on the question of why the sun shines, and introduces various explanations proposed by people from ancient times to the present, including the theory of coal ball combustion, the theory of meteorite impact, and the theory of gravitational contraction. Finally, with the development of atomic physics, it is clear that the energy source of the sun's light comes from the thermonuclear fusion reaction of hydrogen atoms in its interior. The mass lost in the reaction is converted into huge energy, providing the sun with a continuous source of light energy.