Units of Distance in Space

The solar system, nearby stars, and distant galaxies require completely different measuring sticks. Discover the astronomical unit, the light-year, and the parsec — the three main units astronomers use to navigate the universe.

40 XP

Reward

10

Questions

5–10 min

Time

Q1 Question 1 of 10

What is one Astronomical Unit (AU)?

The distance light travels in one year The average distance between Earth and the Sun — about 149.6 million km The diameter of the Sun The distance from Earth to the Moon

Q2 Question 2 of 10

Neptune orbits the Sun at an average distance of about 30 AU. What does this mean?

Neptune takes 30 days to orbit the Sun Neptune is 30 light-years from the Sun Neptune is about 30 times farther from the Sun than Earth is Neptune's diameter is 30 times larger than Earth's

Q3 Question 3 of 10

Which unit is best for measuring the distance to nearby stars like Proxima Centauri (4.2 light-years away)?

Kilometres — the metric system is always most accurate Astronomical Units (AU) — the standard unit for all space distances Light-years or parsecs — both are appropriate for interstellar distances Miles — because NASA uses the imperial system

Q4 Question 4 of 10

One light-year is approximately how many kilometres?

About 9.46 million km About 9.46 billion km About 9.46 trillion km (9,460,000,000,000 km) About 9.46 quadrillion km

Q5 Question 5 of 10

A parsec equals approximately how many light-years?

About 1 light-year About 3.26 light-years About 10 light-years About 100 light-years

Q6 Question 6 of 10

The Milky Way galaxy is about 30 kiloparsecs in diameter. How many parsecs is one kiloparsec?

100 parsecs 1,000 parsecs 1,000,000 parsecs 10 parsecs

Q7 Question 7 of 10

Which unit would a professional astronomer most likely use to describe the distance to the Andromeda Galaxy, which is about 2.5 million light-years away?

About 2.5 million AU About 0.77 megaparsecs (Mpc) About 7.7 gigaparsecs (Gpc) About 77 kiloparsecs (kpc)

Q8 Question 8 of 10

How many Astronomical Units (AU) equal one light-year?

About 365 AU — one AU per day in a year About 6,324 AU About 63,241 AU About 632,410 AU

Q9 Question 9 of 10

Why do astronomers use different units of distance for different scales rather than just using kilometres for everything?

Each country uses different units and astronomers have not agreed on one standard The numbers become impractically large — a unit like the light-year makes distances easier to express and understand Kilometres are not accurate enough for astronomical measurements Different units apply different physical forces — parsecs measure gravity and light-years measure light

Q10 Question 10 of 10

The Oort Cloud — the distant reservoir of comets surrounding our solar system — may extend up to about 100,000 AU from the Sun. How does this compare to one light-year?

It is only 0.01 light-years — tiny compared to the distance to stars It is exactly 1 light-year — which is why a light-year was defined the way it was It is about 1.6 light-years — nearly halfway to the nearest star It is about 100 light-years — far beyond the nearest star

Report a Problem