What is the fundamental building block of the universe according to the passage?

• Galaxies

• Stars

• Solar systems

• Planets

How many galaxies are estimated to be in the observable universe?

• Over 100 billion

• About 100 million

• Approximately 1 trillion

• Less than 1 billion

What is a light-year?

• The distance light travels in one year

• The time it takes for light to travel from the Sun to Earth

• The distance from Earth to the nearest star

• The time it takes for light to travel across the Milky Way

What unit is used to measure distances within our solar system?

• Astronomical unit (AU)

• Light-year

• Kilometer

• Parsec

How far is Proxima Centauri from Earth?

• About 4.24 light-years

• Approximately 1 AU

• Roughly 9.46 trillion kilometers

• Nearly 5.2 AU