How are cepheid variables related to the instability strip?

Related questions

• What is a cepheid variable?
• How are cepheid variable stars found?
• How are cepheid variable stars used in astronomy?
• How are cepheid variable stars used in determining distances?
• Why are cepheid variables important?
• How can a cepheid variable indicate distance?
• How can cepheid variables be used to find distance?
• What are cepheid variable stars and why are they important?
• Where are the cepheid variables? Can we see any from earth without a telescope?
• How can astronomers use variable stars to find distance?