Cosmic Yardsticks

A cosmological measuring tapeThis is the spiral galaxy NGC 3021 which lies about 100 million light-years away in the constellation of Leo Minor (The Little Lion).

This galaxy contains several Cepheid variable stars which can be used work out the distance to the galaxy. These stars pulsate at a rate that is closely related to their intrinsic brightness. Measurements of their rate of pulsation and their observed brightness provide information used to calculate the distance to them and, thus, the galaxy itself.

NGC 3021’s Cepheids were also used to calibrate another even brighter distance marker that can be used over greater distances: a Type Ia supernovae. One of these bright explosions was observed in NGC 3021 in 1995.

Image Credit: ESA

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