Cepheids are highly luminous, variable stars in which the period of variability is directly related to luminosity. explain why cepheids are good indicators for determining stellar distances that lie beyond the limits of accurate parallax measurements.

Aplane travels 1000 miles in 5 hours .what is the planes average speed?

Africtionless piston-cylinder contains 50 l of saturated liquid r-134a. the piston has a mass and an area resulting in an applied pressure of 500 kpa on the refrigerant. the refrigerant is now heated until its temperature rises to 70∘c. calculate the work (in kj) done during this process.

Which lists the fundamental forces in order, from strongest to weakest? strong nuclear, weak nuclear, electromagnetic, gravitational strong nuclear, electromagnetic, weak nuclear, gravitational gravitational, weak nuclear, electromagnetic, strong nuclear electromagnetic, gravitational, strong nuclear, weak nuclear