# Solar-system structure and scale

> The Sun is a star at the centre of the planetary system. Planets, moons, small bodies, gas and dust form a gravitationally interacting system.

Course: [Space and astronomy foundations](https://studybrix.com/en/courses/space-and-sky-foundations/index.md)
Level: school
Prerequisites: Fractions, ordering and basic gravity.

## Notes

### Architecture

The Sun is a star at the centre of the planetary system. Planets, moons, small bodies, gas and dust form a gravitationally interacting system.

### Categories

A planet, a moon and a star are different kinds of object. A moon orbits a larger nonstellar body; stars sustain fusion during their main-sequence phase.

### Distance units

An astronomical unit is a defined length close to the mean Earth-Sun distance. Light-years also measure distance, not time.

### Scale models

One scale rarely shows both body sizes and orbital distances conveniently. State what is scaled and what has been exaggerated.

## Practice questions

### 1. What kind of astronomical object is the Sun?

A. A moon
B. A comet
C. A star
D. A rocky planet

Answer: A star

Explanation: The Sun is the star of the solar system.

### 2. What does a light-year measure?

A. Brightness
B. A telescope's exposure time
C. A star's age by definition
D. Distance

Answer: Distance

Explanation: It is the distance light travels in a year under the defined convention.

### 3. In a model where 1 AU is 2 cm, how far is an object at 5 AU from the origin?

Answer: 10 cm

Explanation: Apply the stated scale: 5×2.

### 4. Two model orbit radii are 3 AU and 9 AU. Find the larger-to-smaller radius ratio.

Answer: 3

Explanation: 9/3=3.

### 5. Which statement is correct about a moon?

A. It must orbit Earth
B. It must make its own visible light
C. It can orbit a planet
D. It must be larger than its planet

Answer: It can orbit a planet

Explanation: Moon is a natural-satellite category, not a synonym for Earth's satellite alone.

### 6. Why can a solar-system poster be misleading if sizes and distances use different scales without labels?

Sample answer / marking guidance: Viewers may infer false size-to-separation relationships. Explicit scale labels and exaggeration notices prevent that confusion.

Explanation: Credit the two scales and the misleading inference.

### 7. Which force primarily binds planetary orbits on solar-system scales?

A. Chemical bonding to the Sun
B. Ordinary friction with space
C. Sound pressure alone
D. Gravity

Answer: Gravity

Explanation: Gravity governs the large-scale orbital interaction.

### 8. Explain why counting only planets does not describe all solar-system matter.

Sample answer / marking guidance: There are also moons, dwarf planets, asteroids, comets, dust and gas, in addition to the Sun. The categories account for different populations.

Explanation: Credit several nonplanet components without requiring changeable inventory counts.

## Further reading

- https://science.nasa.gov/solar-system/

Original AI-assisted educational draft; not independently teacher-reviewed. References support further study, not copied exercises, affiliation or curriculum accreditation.