March 28, 2019
A birthday is what happens when cosmic time briefly puts down the scale of eons and pays attention to a single human year.
The Gaia Stars of M15
Birthday · March 28, 2019
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APOD published March 28, 2019. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
Messier 15 is a 13 billion year old relic of the early formative years of our galaxy, one of about 170 globular star clusters that still roam the halo of the Milky Way. About 200 light-years in diameter, it lies about 35,000 light years away toward the constellation Pegasus. But this realistic looking view of the ancient globular star cluster is not a photograph. Instead it's an animated gif image constructed from remarkably precise individual measurements of star positions, brightness, and color. The astronomically rich data set used was made by the sky-scanning Gaia satellite which also determined parallax distances for 1.3 billion Milky Way stars. In the animated gif, twinkling stars are M15's identified RR Lyrae stars. Plentiful in M15, RR Lyrae stars are evolved pulsating variable stars whose brightness and pulsation period, typically less than a day, are related.