Exercise
• Betelgeuse is classified M2 Ib, and its apparent magnitude is about 0.4. Estimate the distance of this star.
• Its distance estimated from the magnitudedistance formula is about 190 pc.
• Measurements made by the Hipparcos satellite are more accurate and reveal the distance to be 131 pc, with an uncertainty of 21 percent, so the result derived from spectroscopic parallax is only approximate.