Here's why:
* Magnitude Scale: The magnitude scale is a way to measure the brightness of stars. Brighter stars have smaller (even negative) magnitudes, while dimmer stars have larger (positive) magnitudes.
* The HR Diagram: The HR Diagram (Hertzsprung-Russell Diagram) plots stars based on their luminosity (intrinsic brightness) and temperature. Stars in the upper right corner of the diagram are the brightest and hottest.
Therefore, a star in the upper right corner of the HR diagram, which is inherently very bright, will have a negative magnitude.
