astronomy college level

Question

What is the magnitude difference for Betelgeuse at 10 pc?

6.506

388

2.5

197^2

Answer 1

Distance modulus m - M = 5 log r - 5. With the 2007 revision of Hipparcos measurements, the parallax is around 6.55 milli-arcsec for a distance of approx 153 pc. Then the difference between apparent magnitude m and the magnitude at 10 pc, M, is 5.9, close to the artificially precise choice of 6.506.