Imaging star clusters
Posted: Fri Nov 11, 2022 4:08 pm
Following on from Brian's post on the double cluster thought that I'd have a go at some of the Cassiopeia star clusters.
For 'real' visual astronomy (remember that?) I always found star clusters to be some of the most attractive objects-- and that imaging never quite seemed to do them justice. Still not quite sure what does work best or even if any general rules exist but having tried a range of exposures on different clusters am generally of the opinion that 1) the clusters that look the best are often the brightest having big coloured overexposed stars and Newtonian spikes and 2) a low stretch often works best so that the cluster itself is better differentiated from background and 3) there is not a lot of point imaging for longer than 20 min or so (at F4.5) - although a brief tour of Astrobin indicates that there is no consensus on any of this.
Anyway here are three ...the double double in the sword arm of Perseus, the dragonfly (or owl) cluster in Cassiopeia and Caroline 's (Herschell) rose,
Personally I think that the dragonfly is the most photogenic?
One curious question that I have. To my perception, stars in star clusters often look like beads on a string - often curved strings with dark circles and lanes between. It is quite reminiscent of - on a much larger scale -the way galaxies also seem to look like beads on curving strings (in that case presumptively along threads of dark matter). Does anyone know why stars might also appear to lie along threads in star clusters? Is that symmetry a natural consequence of the way radiation from one star igniting might help trigger ignition of a star close by within star-forming molecular clouds and thus end up forming a line of stars aligned with a ridge of higher molecular cloud density ?
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SW PDS200 Newtonian down to F 4.5 (1.05 arcsec/ pixel)using the SW 0.9X reducer/ coma corrector, OSC AS1294 MC, 33s exposure at gain 124 frames all captured using Sharcap 4 and guided using PHD2 on a CEM70 mount. Bortle 6 skies with the moon up and 1 day past full.
NGC 869/ NGC 884 = 51 x 33s exposures
NGC 457 = 91 x 33s exposures
NGC7789 = 55 x 33s exposures
For 'real' visual astronomy (remember that?) I always found star clusters to be some of the most attractive objects-- and that imaging never quite seemed to do them justice. Still not quite sure what does work best or even if any general rules exist but having tried a range of exposures on different clusters am generally of the opinion that 1) the clusters that look the best are often the brightest having big coloured overexposed stars and Newtonian spikes and 2) a low stretch often works best so that the cluster itself is better differentiated from background and 3) there is not a lot of point imaging for longer than 20 min or so (at F4.5) - although a brief tour of Astrobin indicates that there is no consensus on any of this.
Anyway here are three ...the double double in the sword arm of Perseus, the dragonfly (or owl) cluster in Cassiopeia and Caroline 's (Herschell) rose,
Personally I think that the dragonfly is the most photogenic?
One curious question that I have. To my perception, stars in star clusters often look like beads on a string - often curved strings with dark circles and lanes between. It is quite reminiscent of - on a much larger scale -the way galaxies also seem to look like beads on curving strings (in that case presumptively along threads of dark matter). Does anyone know why stars might also appear to lie along threads in star clusters? Is that symmetry a natural consequence of the way radiation from one star igniting might help trigger ignition of a star close by within star-forming molecular clouds and thus end up forming a line of stars aligned with a ridge of higher molecular cloud density ?
------------------------------------------------------------------------------------------
SW PDS200 Newtonian down to F 4.5 (1.05 arcsec/ pixel)using the SW 0.9X reducer/ coma corrector, OSC AS1294 MC, 33s exposure at gain 124 frames all captured using Sharcap 4 and guided using PHD2 on a CEM70 mount. Bortle 6 skies with the moon up and 1 day past full.
NGC 869/ NGC 884 = 51 x 33s exposures
NGC 457 = 91 x 33s exposures
NGC7789 = 55 x 33s exposures