1. Why is it useful to plot the apparent magnitudes of stars in a single cluster on an H-R diagram? 2. What might happen to the massive outer planets when the Sun becomes a giant? 3. How many 1.5-M...

1. Why is it useful to plot the apparent magnitudes of stars in a single cluster on an H-R diagram?

2. What might happen to the massive outer planets when the Sun becomes a giant?

3. How many 1.5-M main-sequence stars would it take to equal the luminosity of one 15-M star?