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Berkeley 17 – The Oldest Open Cluster in the Milky Way

October 23, 2011 Leave a comment

The Berkeley Open Cluster catalogue contains 104 clusters observed by astronomers at the University of California, Berkeley using the Palomar Observatory Sky Survey (POSS) plates. The catalogue was published in 1958 by Jiri Alter et al.  The Berkeley clusters are a fascinating and challenging group to explore and contain some of the oldest and most distant open clusters in our galaxy. Over the next few months i’m going to introduce you to a few of these clusters with the help of some images taken using the GRAS remote telescopes in New Mexico.

Berkeley 17 (Be17) is found in the constellation Auriga and currently holds the title for the oldest open cluster in our galaxy. There is some dispute over the maximum age estimate depending on which astronomical paper you read,  but the average figure is somewhere around 10.06 – 10.08 billion years old (a 2006 paper gives a date range of 8.5- 9 billion years, but does not rule out a greater age) . Be17 does have a rival for oldest open cluster, NGC 6791 in Lyra, but until a definitive date range is provided for the latter Be17 reigns supreme.

Like most of the Berkeley clusters Be17 is very faint with magnitudes of its estimated 400 member stars in the range 17.8 – 20.0. It appears as a slightly more dense clump in the centre of the photo below and is largely populated by old red stars of relatively high metallicity with no evidence of any blue stragglers which are more common in older globular clusters. Be17 is thought to inhabit the thin disk of our galaxy and therefore helps to date the formation of the thin disk as well as supplying an upper date limit for the formation of the thick disk and halo.

Imaged using GRAS 03  TAK TOA 150/FLI ML8300 one shot colour camera. 24th September 2011 09:11:37 UTC   RA: 05h 20m 32.0s DEC: 30° 34′ 30″ (J2000)  20 minutes exposure @ 2 x 600 seconds.

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Categories: Stars & Star Clusters

The Sun – 15th October 2011 – Lots of surface activity

October 15, 2011 Leave a comment

Lovely clear blue skies today, but with loads of atmospheric jitter so close up images of the activity were not possible. These Ha and CaK images were taken between 10.30 and 12.30 UT. There are seven active regions gliding over the surface of the sun with lots of nice spot, filament and pore detail. Active regions in the images include 1312, 1313, 1318 on the right and 1314, 1316, 1317, 1319 on the left.

 

Categories: Solar

M13 Globular Cluster in Hercules

October 7, 2011 Leave a comment

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.

Categories: Stars & Star Clusters

The Sun 30-9-11 AR1302 & Filaments

October 1, 2011 Leave a comment

There are currently five active regions forming a band of activity across the sun today including AR1301, 1302, 1305, 1306 and 1307. AR 1302 has given us some pretty impressive flares, but seems to be approaching the western limb in a rather subdued state. Although quiet AR1302 still harbors the magnetic strength to produce some X-Class flares and is still very dynamic visually with some impressive active region filaments arcing high above the main sunspots at its core.  Images taken 12.10-12.55 UTC+1 with PST Ha, PST CaK, DMK41.

Ha Disk

CaK Disk

Close up of AR1302 and its arching filaments. AR 1305 to left

CaK of AR 1302 (right) and AR 1305 (left)

Categories: Solar