Q 01/05

Despite the word 'year' in its name, a light-year is a unit of what?

A) Speed

B) Time

C) Length

D) Brightness

Answer · why

C) Length

Length: a light-year is the distance light covers in one year, so anything you see a light-year away appears as it was a year ago.

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

9.46 trillion kilometres is about 5.88 trillion miles; it is simply the speed of light multiplied by the 8,766 hours in a year, so nobody ever had to ...

Q 03/05

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

A) The European Space Agency

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 International Astronomical Union, the same body that demoted Pluto to dwarf planet in 2006, fixes the light-year using the Julian year of exactly ...

Q 04/05

Which space telescope, launched in 2021, was built to catch light that has travelled for over 13 billion years?

A) Hubble

B) James Webb

C) Herschel

D) Chandra

Answer · why

B) James Webb

James Webb sits 1.5 million kilometres from Earth behind a sunshield the size of a tennis court, because its own warmth would otherwise drown the fain...

Q 05/05

What is the standard abbreviation astronomers use for the light-year?

A) ltyr

B) lgy

C) lty

D) ly

Answer · why

D) ly

ly is the accepted symbol, yet professional astronomers mostly work in parsecs and leave the light-year to popular science writing.