In the vast expanse of the universe, there are countless islands with different poses and expressions, inhabited by stars and various celestial bodies. These islands are known as galaxies in astronomy.

Our home planet, Earth, is situated in a colossal galaxy - the Milky Way. There are hundreds of millions of space giants, similar to the Milky Way, in the universe outside of it. They are collectively known as extragalactic galaxies.

The center of the Milky Way is about 25,000 light-years away from the sun. However, we cannot see the center of the Milky Way as our view is blocked by dense clouds of nebulae, gas, and dust between the sun and the center of the Milky Way.

There are billions of galaxies in the universe, and astronomers categorize most of them into three types: spiral galaxies, elliptical galaxies, and irregular galaxies. Each galaxy has the unique characteristics that make it distinct.

While there are many galaxies in the universe, only a few can be seen with the eye, including the Andromeda Galaxy, which is about 2 million light-years away from Earth.

The Andromeda Galaxy looks similar to the Milky Way and is about 60% larger in volume. When seen with the eye, it appears as a small spot resembling a star.

Typically, during the day, we can only see the sun and the moon, but not the stars. Does this mean that the stars disappear during the day? Not really.

During the day, the strong sunlight shines on the earth's atmosphere and enters our eyes after being scattered by atmospheric molecules. We can only see the blue sky. The light emitted by stars is too weak to be discerned by the human eye as it is insignificant compared to the sun's light. Therefore, we cannot see the stars during the day.

When we look up at the sky, we see celestial bodies such as planets, satellites, meteors, and comets.

Planets are celestial bodies that orbit the sun, including Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Over time, we can observe their trajectories and surface features through telescopes.

Satellites are celestial bodies that orbit planets, including the moon, Io, and Titan. We can observe some bright satellites, such as the moon, through a telescope or with the eye.

Meteors are small meteorites that burn up in the Earth's atmosphere, commonly known as "meteor showers." A meteor streaking across the sky is a beautiful astronomical phenomenon. Annual meteor shower seasons usually occur at specific times, such as the Perseids in August and the Geminids in December.

Comets are small bodies of ice and dust floating in the solar system, often called "dirty snowballs." Comets increase in brightness as they approach the sun, forming a bright tail.

In addition to these celestial bodies, we can also observe nebulae and star clusters in the Milky Way.

Nebulae are clouds of gas and dust, some of which are very bright, such as the Large Magellanic Cloud and the Cat's Eye Nebula. A star cluster is a dense group of stars, usually divided into two types: globular clusters and open star clusters.

The starry sky is full of mysterious celestial bodies and beautiful scenes. We can gain a deep understanding of them through observation and learning, and feel the magic and magnificence of the universe. Studying astronomy allows us to expand our horizons and appreciate the vastness of the cosmos.

We can learn about the stars and their evolution, the composition of galaxies, and the exploration of other planets. Astronomy is an exciting and constantly evolving field of science, and it enables us to explore the mysteries of the universe.