Q 01/05

A light-year is a unit of what?

A) Speed

B) Time

C) Length

D) Brightness

Answer · why

C) Length

Despite the word year, it measures how far light travels in one Julian year of 365.25 days.

Q 02/05

Approximately how many kilometres is one light-year?

A) 9.46 trillion

B) 94.6 trillion

C) 946 trillion

D) 9.46 quadrillion

Answer · why

A) 9.46 trillion

That is about 5.88 trillion miles.

Q 03/05

Which body's definition of the light-year is based on the Julian year of 365.25 days?

A) NASA

B) The International Bureau of Weights and Measures

C) The International Astronomical Union

D) The Royal Society

Answer · why

C) The International Astronomical Union

The Julian year is used rather than the 365.2425-day Gregorian year or the tropical year.

Q 04/05

Neighbouring galaxies are typically separated by distances of what order?

A) Billions of light-years

B) Trillions of light-years

C) Thousands of light-years

D) Millions of light-years

Answer · why

D) Millions of light-years

Galaxies themselves span a few thousand to a few hundred thousand light-years.

Q 05/05

What is the IAU abbreviation for light-year?

A) ltyr

B) lgy

C) lyr

D) ly

Answer · why

D) ly

French, Spanish and Italian use al, and German uses Lj for Lichtjahr.

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