Astronomy Practice Exam

What is the numerical value of one light year in kilometers?

1. About 300 million kilometers

2. About 300 billion kilometers

3. About 10 trillion kilometers

4. About 1 million kilometers

The correct answer is: About 10 trillion kilometers

One light year is the distance that light travels in a vacuum in one year. To understand this distance numerically in kilometers, we start by recognizing the speed of light, which is approximately 299,792 kilometers per second. To calculate the distance of one light year, you first convert one year into seconds. There are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day. Thus, one year has about: 60 seconds/minute × 60 minutes/hour × 24 hours/day × 365 days/year ≈ 31,536,000 seconds. Next, by multiplying this number by the speed of light: 31,536,000 seconds/year × 299,792 kilometers/second ≈ 9.46 trillion kilometers. This illustrates that one light year is approximately 9.46 trillion kilometers, making it reasonable to state that this value can be rounded to about 10 trillion kilometers. This understanding is critical, especially in contexts where astronomical distances are compared. Distances in space are vast, and using light years as a measure helps convey those astronomical scales effectively.