2007

How far away is the K star?

Round: Theory
Points: 2
Level: Bronze
Taught in: Section 4.1

Adapted from IOAA 2007 (Chiang Mai), theory problem 1.10. We have restated it in our own words and kept the original data. The solution was last checked on 20 October 2026.

A main-sequence star of type K has a luminosity of $0.4 L_{⊙}$ , and its flux at Earth is $6.23 \times 10^{- 14}$ W m⁻². How far away is it, in parsecs? Ignore the atmosphere, and take $L_{⊙} = 3.828 \times 10^{26}$ W and 1 pc $= 3.086 \times 10^{16}$ m.

I solved it without the solution

AnswerThe star is about 453 pc away.

This problem also appears among the olympiad problems of Section 4.1, Flux and luminosity, which teaches the ideas it uses. Equation and figure numbers refer to the course.