Shanghai Edition Junior High School Science, Grade 9, Part 2: Our Cosmic Address

From Microscopic Spirals to Macroscopic Arms

Imagine that the origin of life is inscribed in the tinydouble helix of DNAand our home world is etched onto the vast spiral arms of the Milky Way. The universe is not chaotic—it is a highly structured system. Starting from Earth beneath our feet, it extends upward through the solar system, theMilky Way, the Local Group, all the way tosuperclusters.On cosmic scales, matter distribution remains consistentlyhomogeneous and isotropic,a cornerstone of modern cosmology.

The Precise Anatomy of the Galaxy

Galactic Core: The central hub of the galaxy, with extremely dense stars. Astronomers speculate that a supermassiveblack holeresides at its center, governing the galaxy’s gravitational core.
Galactic Disk and Spiral Arms: The main body of the galaxy, resembling a glowing record. The Sun orbits the galactic center at about 250 km/s—this large-scale revolution parallels microscopicBrownian motion,in revealing the universality of motion in matter.
Cosmic Hierarchy: We are not alone. The Milky Way, along withAndromeda Galaxyand others, form theLocal Group,the fundamental unit for larger-scalegalaxy clusters.的基本单位。

From Herschel’s flat-disk model to today’sfinite but unbounded universe model,human understanding of space and time has never ceased evolving. The emergence of early life 3.5 billion years ago to humanity today measuring the stars throughscience and technologyis itself the most magnificent chapter in human civilization’s evolution within the cosmos.human civilization在宇宙演化史中最华丽的篇章。

QUESTION 1

Use your scientific knowledge to match the following galactic concepts: (A) Galactic Center, (B) Sun’s Position, (C) Neutron Star Mass Limit, (D) Galactic Neighbor, (E) Dense Star Region

A-1 (Galactic Core), B-2 (Orion Arm), C-3 (Oppenheimer Limit), D-4 (Andromeda Galaxy), E-5 (Star Cluster)

A-2, B-1, C-4, D-3, E-5

A-5, B-3, C-1, D-2, E-4

QUESTION 2

What is the approximate speed and period of the Sun’s orbit around the galactic center?

250 km/s, approximately 250 million years

30 km/s, approximately 1 year

1000 km/s, approximately 1 billion years

QUESTION 3

In the cosmic hierarchy, what is the term for a group of about 50 galaxies, including the Milky Way and Andromeda Galaxy?

Solar System

Local Group,

superclusters.

QUESTION 4

According to scientific evolutionary models, when did primitive life on Earth first appear?

4.6 billion years ago

3.5 billion years ago

250 million years ago

QUESTION 5

What type of celestial object do astronomers suspect exists at the center of the Milky Way (the galactic core)?

A typical red dwarf star

Supermassive black hole

A massive comet swarm

Civilization, Technology, and Cosmic Evolution

Exploring how humanity has evolved from Earth to deep space

The history of human civilization is fundamentally a story of expanding measurement tools and cognitive boundaries. From the inheritance of primitive traits to the concept of interstellar travel, every step has been driven by science and technology.

1. [Writing Task] Research historical developments of timekeeping devices and discuss their relationship with human civilization progress. (Word count requirement: 500 words)

Answer:
Timekeeping devices have evolved from sundials and hourglasses to pendulum clocks and atomic clocks. Each leap in precision has directly driven civilizational progress. During the Age of Exploration, accurate timekeeping was crucial for determining longitude, enabling global discovery. In modern physics, atomic clocks verify time dilation and length contraction predicted by relativity. Each advance in timing accuracy marks an increase in humanity’s control over natural laws—demonstrating the core role of science and technology in driving productivity.

2. [Case Analysis] Choose one of China’s Four Great Inventions (e.g., compass or papermaking) and discuss its impact on human civilization progress. (Word count requirement: 200 words)

Answer:
Take papermaking as an example: it provided an affordable and efficient medium for preserving and spreading scientific knowledge, breaking the monopoly on information. Without papermaking’s democratization of information, the emergence of modern science and global civilizational connectivity would be unimaginable. By accelerating the 'inheritance' and evolution of knowledge, it laid the foundation for modern civilization.

3. [Scientific Inquiry] Describe the birth and evolution of stars, and explain whether the universe is static or dynamically evolving?

Answer:
Stars are born from collapsing nebulae, evolve through the main sequence stage, and then may become red giants, white dwarfs, or leave behind neutron stars or black holes after supernova explosions (subject to the Oppenheimer limit). The universe is not static—it has been continuously expanding and evolving since the Big Bang. This dynamism proves that the universe is a complex, ever-evolving system.