Observations of collapse
• Young cluster “NGC 2264”
– Few million years old
• High mass stars have reached
main sequence
• Lower mass stars are still
approaching main sequence
– T Tauri stars
• Naming of classes of stars:  Usually
named after first star in class:  T
Tauri
– Stars with letters (RR Lyrae) are
typically “variable” stars
• Earlier stages hidden by dust