ASTR 1050

The Period-Luminosity Relationship

•Relationship discovered by Henrietta Leavitt in 1912

–stars in Small Magellanic Cloud

–all at roughly same distance

–but didn’t have absolute M, just apparent M

–need absolute M to get distances

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•Calibrated by Harlow Shapley

–If you can find distance (so M-m) for just one nearby Cepheid, you can convert Leavitt’s “m” scale to the “M” you want.

From our text: Horizons, by Seeds