Which year did Ole Roemer discover that light travels approximately 186,000 miles per second in space?

Which year did Ole Roemer discover that light travels approximately 186,000 miles per second in space?

• A. 1675
• B. 1775
• C. 1575
• D. 1875

Answer: (A)

The main idea here is that light has a finite speed, which Roemer demonstrated by using observations of Jupiter’s moon Io. He tracked Io’s eclipses and compared when they should occur with when they actually occurred from different points in Earth’s orbit. When Earth was farther from Jupiter, the eclipses appeared to happen later than predicted; when closer, sooner. The accumulating delays matched the time light would take to travel the changing distance, allowing Roemer to estimate light’s speed at about 186,000 miles per second. This work happened in the 1670s, with the decisive results around 1676, and in many exams the year given for this discovery is the nearby 1675. Among the options, that era is the correct pick.

The main idea here is that light has a finite speed, which Roemer demonstrated by using observations of Jupiter’s moon Io. He tracked Io’s eclipses and compared when they should occur with when they actually occurred from different points in Earth’s orbit. When Earth was farther from Jupiter, the eclipses appeared to happen later than predicted; when closer, sooner. The accumulating delays matched the time light would take to travel the changing distance, allowing Roemer to estimate light’s speed at about 186,000 miles per second. This work happened in the 1670s, with the decisive results around 1676, and in many exams the year given for this discovery is the nearby 1675. Among the options, that era is the correct pick.