Another demonstration of proper motion

Not long ago, I blogged about a guy who took an image of a starfield and compared it to Palomar images from fifty years ago to show stars altering their positions in the night sky due to proper motion (their actual parallel motion relative to the Sun). Now the Hubble Space Telescope, which takes its image in higher resolution, allowing smaller movements to be tracked over a shorter period of time, has also released some images showing proper motion occurring in a cluster of stars. NGC 3603, also known as the Young Cluster, is 20,000 light years from us. The images were taken more than a decade apart, with one found in archives in July 1997 and the other taken for the purpose in September 2007, both using the Wide Field Planetary Camera 2 and the same filter set. The images are here. They weren’t actually taken to show off proper motion, but to use it to map the velocity structure of the gravitationally bound cluster. What they found was that the velocities haven’t yet settled down into orbital velocities determined by mass yet and instead still show deviations caused by the conditions prevalent at the creation of the cluster.

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