Final answer:
An astronomer studying a system hundreds of billions of kilometers across would use the Astronomical Unit (AU) for within the solar system and the light-year for distances beyond. The AU is the average distance between the Earth and the Sun, while the light-year is the distance light travels in one year.
Step-by-step explanation:
When studying a solar system that spans hundreds of billions of kilometers, astronomers must utilize units of measure that can feasibly represent such vast distances. Instead of using kilometers, which become cumbersome over astronomical distances, two primary units are used:
- Astronomical Unit (AU): Defined as the average distance from Earth to the Sun, equating to approximately 149,597,870.7 meters or about 8.3 light-minutes. This unit is particularly useful for measuring distances within our own solar system.
- Light-year: The distance light travels in one year, which is about 9.5 trillion kilometers (or 9.5 × 1012 kilometers). This is a beneficial unit when discussing distances to stars and other celestial bodies outside of the solar system.
For instance, to calculate the distance from the Sun to Saturn in AUs, we would take the distance in kilometers (1.4 billion kilometers) and divide it by the length of one AU (approximately 150 million kilometers), yielding a result in AUs.
When surveying distances that extrend beyond the solar system, astronomers also use the parsec, which is equivalent to 3.26 light-years, and helpful when measuring distances between stars and galaxies. The parsecs and light-years are both integral to the scale model visualization and understanding of interstellar and intergalactic distances.