1 Sketch an H-R diagram of the evolutionary path of the Sun.2 Sketch an H-R diagram of the evolutionary path of a 15Msun star.3 Describe how a protostar is believed to form.4 What heats a protostar?5 What is a bipolar flow?6 How can we observe protostars? Why are they surrounded by dust and gas?7 What is a T Tauri star?8 What is a Bok globule?9 What determines when a star becomes a main-sequence star?10 What determines how long a star stays on the main sequence?11 What makes a star move off the main sequence?12 Where do main-sequence stars end up as they evolve?13 Why do high- and low-mass stars evolve differently as they become red giants?14 Why is it easier for a high-mass star than for a low-mass star to burn helium?15 What is meant by a pulsating star?16 Why do stars pulsate?17 What happens to a solar-mass star when it starts to burn helium in its core? What does it turn into?18 What is a planetary nebula?19 What is one explanation for how a low-mass star expels its outer layers to make a planetary nebula?20 What is left when a planetary nebula dissipates?21 What makes a high-mass star's core collapse?22 How do the neutrons form in a massive star's remnant core? What other kind of particle is made along with the neutrons?23 What is a supernova explosion?24 What kind of subatomic particles have been observed when a supernova explodes?