Knowledge Point 01: The Reason for Stars Twinkling
The twinkling of stars is not due to changes in their own luminosity, but rather due to variations in atmospheric density and thickness, causing refraction and scattering of starlight as it passes through, thus producing the twinkling effect.
Detailed Explanation:
When we gaze at the night sky, we often notice stars twinkling. This is not because the luminosity of the stars themselves is changing, but rather due to uneven distributions of air density and thickness in the atmosphere.
As starlight passes through this complex atmosphere, it encounters air layers of different densities and thicknesses, causing refraction and scattering of the light. This refraction and scattering create slight variations in the position and brightness of the stars we observe, resulting in the twinkling effect.
Knowledge Point 02: The Reason for the Blue-Green Color of Seawater
Seawater appears blue-green due to its absorption and reflection of light, where green light is absorbed less by seawater and reflected, while deeper seawater absorbs green light and reflects blue light.
Detailed Explanation:
When we look out at the sea, we often see it appearing blue-green. This is caused by the absorption and reflection of light by seawater. Seawater itself is colorless, but it contains various tiny particles and dissolved salts that have specific effects on the absorption and reflection of light.
In the visible spectrum, green light is absorbed relatively little by seawater. Therefore, when the seawater is shallow, green light can be reflected, making the sea appear green. When the seawater is deeper, green light is also absorbed, while blue light is relatively more easily reflected, making deep seawater appear blue.
Knowledge Point 03: The Scale of the Milky Way Galaxy
The Milky Way Galaxy is a vast galaxy, approximately 80,000 light-years wide and 12,000 light-years thick at its center, containing over 100 billion stars and serving as the home of the solar system.
Detailed Explanation:
The Milky Way Galaxy, the galaxy in which we reside, is astonishingly vast in scale. It spans approximately 80,000 light-years in width and is about 12,000 light-years thick at its center. This enormous galaxy contains over 100 billion stars, which collectively form this dazzling galaxy.
The Milky Way is not only the home of our solar system but also a gathering place for countless other planets, moons, nebulae, and interstellar matter. Its grandeur and mystery have always attracted humans to explore and understand it.
Knowledge Point 04: The Reason Why Stars Are Not Visible During the Day
Stars are not visible during the day due to the intense sunlight and atmospheric scattering that brighten the sky, masking the faint light of the stars.
Detailed Explanation:
During the day, it is difficult to see stars because sunlight is very intense, and the gases and dust in the atmosphere scatter sunlight, making the sky very bright.
In contrast, the light of stars is very faint and is easily obscured by sunlight and the bright sky during the day. Only at night, when the sun sets and the sky darkens, can we clearly see the light of the stars.
Knowledge Point 05: The Composition of Celestial Bodies in the Solar System
The solar system is composed of eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), Pluto (now classified as a dwarf planet), and numerous asteroids, comets, and meteors.
Detailed Explanation:
The solar system is the stellar system in which we reside, consisting of eight planets orbiting the sun. These planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Additionally, the solar system includes dwarf planets like Pluto, as well as numerous asteroids, comets, and meteors. These celestial bodies collectively contribute to the richness and diversity of the solar system, providing valuable opportunities for us to explore the universe and understand the evolution of the solar system.
Knowledge Point 06: The Height of the Blue Sky
“Blue sky” is actually Earth’s atmosphere, which has a thickness of about 2,000-3,000 kilometers, but most of the air is concentrated within a height of 15 kilometers above the ground.
Detailed Explanation:
When we look up at the blue sky, we may wonder how high it goes. In fact, “blue sky” is a visual effect created by the scattering of sunlight by Earth’s atmosphere.
The atmosphere surrounds the air of Earth and has a thickness of about 2,000-3,000 kilometers. However, most of the air is concentrated within a height of 15 kilometers above the ground.
As height increases, the air becomes thinner. Therefore, although the atmosphere is thick, the “height” of the blue sky mainly refers to the denser part of the atmosphere.
Knowledge Point 07: The Principle of Thunder
Thunder is a natural phenomenon produced when negative and positive electricity meet and discharge in the atmosphere, accompanied by intense light and sound.
Detailed Explanation:
Thunder is an awe-inspiring natural phenomenon. When clouds in the sky carry different charges (usually negative and positive electricity), they create an electric field between them.
When the electric field strength is sufficient, negative and positive electricity meet and discharge in the atmosphere, forming lightning. This process releases tremendous energy, producing intense light and sound. This is what we commonly refer to as thunder.
Knowledge Point 08: The Reason for the Red Sky in the Morning and Evening
The red sky in the morning and evening is caused by the scattering of sunlight in the atmosphere, where longer wavelength red light is scattered less and thus reaches our eyes more frequently.
Detailed Explanation:
In the morning and evening, we often notice the sky appearing beautifully red. This is because as sunlight passes through the atmosphere, it is scattered by atmospheric molecules. During this process, shorter wavelength blue and violet light are scattered more, while longer wavelength red light is scattered less.
Therefore, when sunlight obliquely enters the atmosphere (as in the morning and evening), red light can pass through the atmosphere more easily and reach our eyes, making the sky appear red.
Knowledge Point 09: The Definition of a Meteor
A meteor is the light trail produced by solid or dust particles in space burning due to friction as they enter Earth’s atmosphere.
Detailed Explanation:
A meteor is a fascinating astronomical phenomenon. When solid or dust particles in space (commonly known as meteoroids) enter Earth’s atmosphere, they rapidly heat up and burn due to friction and collisions with atmospheric molecules.
This process produces a bright light trail, which is what we commonly refer to as a meteor. The appearance of meteors is often accompanied by beautiful light and tails, inspiring people with endless imagination and longing.
Knowledge Point 10: The History of Halley’s Prediction of a Comet’s Return
Halley was the first astronomer to successfully predict the return of a comet by observing and analyzing its motion trajectory and predicting its periodic return.
Detailed Explanation:
Halley was an outstanding astronomer who became famous for successfully predicting the return of a comet. In Halley’s time, many comets had been observed to appear and disappear, but little was known about the nature and motion patterns of these celestial bodies.
By carefully observing and analyzing the motion trajectory of a particular comet, Halley discovered that it seemed to have a periodic return pattern.
Based on this discovery, Halley made a bold prediction: this comet would return at some point in the future. Subsequent events proved his prediction correct, and the comet was named Halley’s Comet in his honor.
Halley’s achievement not only pushed forward the development of astronomy but also provided important insights for our understanding of celestial motion in the universe today.
