Home > Stars & Star Clusters > M13 Globular Cluster in Hercules

M13 Globular Cluster in Hercules

Summer is traditionally the time for amateur astronomers to observe and image the globular clusters that inhabit the outer halo of our galaxy as the dense starfield and dust clouds in the galactic plane of the Milky Way do not obscure our view at this time. I left it quite late this year to take a look at the Northern Hemisphere’s finest globular cluster and chanced on it quite by accident while imaging some open clusters for a series of future blog posts.

M13 is the brightest globular in northern skies with a naked eye magnitude of 5.7 and is visible as a fuzzy star in dark skies free of light pollution. There are around 600,000  gravitationally bound stars around and within its tight core and it orbits the Milky Way every 500 million years on an elliptical path extending up to 80,000 light-years from the galactic centre at its furthest point of travel. Like all globulars it is an extremely old object and has a Universe defying estimated age of 14 billion years (the Universe is 13.75 billion years old). This age may ultimately be revised down but currently, along with some other stubborn globulars like NGC 5286 (15 – 17 billion years old), it refuses to conform to the accepted age range. The scatter of globulars around the halo of our galaxy effectively marks the former extent of the galaxy during its earliest stages of development and well before the recognizable spiral arms developed around the inner core. In common with other globulars the constituent stars are generally very old red giants nearing the end of their life and the metal content is typically low, but there are a number of bright blue stars called Blue Stragglers in the core which are much younger. Blue Stragglers are thought to form from collisions or mergers between the tightly packed stars in the core.

Imaged 8.57 pm 30/9/11 using GRAS G3 (Takahasi TOA 150 refractor/FLI ML8300 one shot color camera) in New Mexico. 20 minute exposure – 2 x 600 sec. RA: 16h 41m 42.0s DEC: 36° 28′ 01″ (J2000). Processed with Maxim DL5/Photoshop CS2.

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Categories: Stars & Star Clusters
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