# How bright could Gliese 710 appear in 1.35 million years?

I read this article on Gliese 710 that stated it would come within about 1.1 ly (+/- 0.577 ly) of earth in 1.35 million years. Wikipedia states it would have an apparent magnitude of 0.5, and the original paper abstract states it would have a -2.7 apparent magnitude.

From reading the list of brightest stars, apparent magnitude of 0.5 would make it about the 10th brightest star, and -2.7 would make it the brightest (besides the sun).

I'm curious about the discrepancy between these sources.

How bright would Gliese 710 appear if it were at the near end (0.523 ly) and far end (1.677 ly) of the expected closest approach to us?

• Calculate it yourself: you can treat it as a point source, so irradiance goes as the square of the distance; magnitudes are a log scale. Jan 6, 2017 at 14:30

## 1 Answer

WolframAlpha says (to the query "apparent magnitude of star with absolute magnitude = 8.23 and distance = 1.1 ly") that the apparent magnitude of Gliese 170 would be about 0.87 on average. I took the value of the absolute magnitude (8.23) from Wikipedia. You can plug in different values for the distance in the formula and see what comes out. The formula used by WolframAlpha is

$$D_l = 10^{{m-M \over 5} +1} pc$$

where $D_l$ = luminosity distance, $m$ = apparent magnitude, $M$ = absolute magnitude, $pc$ = parsec.