NGC 3021 NICMOS/ACS detail 4

This image is part of a montage of images of the spiral galaxy NGC 3021 taken by the NASA/ESA Hubble Space Telescope. Hubble made precise measurements of Cepheid variable stars in the galaxy, highlighted in this image. These stars pulsate at a rate that is matched closely to their intrinsic brightness. This makes them ideal for measuring intergalactic distances. The Cepheids are used to calibrate an even brighter milepost marker that can be used over greater distances, a Type Ia supernova. The supernova was observed in the galaxy in 1995. The image was taken with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).