Q6. Which one of the following is a reason why astronomical distances are measured in light-years?
a) Distances among stellar bodies do not change. b) The gravity of stellar bodies does not change. c) Light always travels in a straight line. d) The speed of light is always the same.
Answer: (d)
Space distance is measured in terms of light years Light-years are used to measure astronomical distances because light travels at a constant speed throughout the cosmos and is extremely precise. Light moves at a speed of 670,616,629 mph (1,079,252,849 km/h) in a vacuum. You multiply this speed by the number of hours in a year to calculate the distance of a light-year (8,766). The answer is that 5,878,625,370,000 miles make up one light-year (9.5 trillion km).
This can appear to be a very far distance at first, but the vastness of the universe dwarfs it. Astronomers can establish how far back in time they are looking by measuring in light-years. Everything we see in the night sky has time to travel through our eyes because light takes time to do so.
