1. What is the common name for the sonic boom created by lightning? 2. What spectral classes of stars are the 5% only found in spiral arms of spiral galaxies? 3. What is the Hubble classification...

1. What is the common name for the sonic boom created by lightning?

2. What spectral classes of stars are the 5% only found in spiral arms of spiral galaxies?

3. What is the Hubble classification scheme? Which category includes the biggest galaxies? Into which category do the smallest galaxies fall? Which type of galaxy is the most common?