Distances: Crash Course Astronomy #25

What observation led ancient Greeks to conclude that the Earth was spherical?

• The changing appearance of constellations throughout the year

• The way ships appeared to sink hull-first below the horizon

• The curved shadow of the Earth on the Moon during a lunar eclipse

• The consistent direction of gravity pulling objects downwards

How did the ancient Greek philosopher Eratosthenes accurately estimate the Earth's circumference?

• By observing the phases of the Moon

• By measuring the time it took for ships to sail around the world

• By using geometry and measurements of shadows in two different cities

• By calculating the distance to the Sun using parallax

What does the Astronomical Unit (AU) represent in astronomy?

• The distance from Earth to the Moon

• The average distance from Earth to the Sun

• The distance from the Sun to the nearest star

• The diameter of the Milky Way galaxy

Which method allowed astronomers to precisely determine the Astronomical Unit in the 1960s?

• Observing the transit of Mercury across the Sun

• Using powerful optical telescopes to measure stellar parallax

• Bouncing radar pulses off the planet Venus

• Analyzing the gravitational pull between Earth and the Moon

What is the phenomenon where your brain combines slightly different images from each eye to perceive depth and distance?

• Monocular vision

• Astigmatism

• Parallax

• Refraction

What serves as the "baseline" for measuring the parallax of distant stars?

• The distance between two telescopes on Earth

• The diameter of Earth's orbit around the Sun

• The distance between Earth and the Moon

• The diameter of the Sun

Which of the following units is defined as the distance light travels in one year?

• Astronomical Unit (AU)

• Parsec

• Light-year

• Kilometer

For stars too distant for parallax measurements, what property can astronomers use to determine their distance, assuming they know the star's intrinsic brightness?

• Their apparent color

• Their apparent brightness

• Their rotational speed

• Their chemical composition