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Star pattern for TML test with light pollution

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#26 WRAK

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Posted 22 April 2013 - 03:59 PM

Share your view that AAVSO is regarding magnitudes what WDS is for double stars - but this does in both cases not mean free from errors. For my purpose I used the Tycho star pattern for M67 (to keep the number of stars reasonable low) but the magnitudes from AAVSO and had the troubles mentioned above. But difficulties like this make it only more interesting to proceed further.
Wilfried

#27 WRAK

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Posted 28 April 2013 - 06:51 AM

A few days ago another opportunity for a look at M67. More or less full moon from behind, NEML 2.5, SQM 17, Pickering 5-6, spurious disk crisp, bit dancing. Meanwhile I know the star pattern of M67 more or less by heart and some training effect is to notice - it seems easier to see the fainter stars now. Both dubious +11.3mag stars in the lower part of M67 are this time ignored. I got the following results:
140mm > 11.8 but less than 12.1 (11.9 and 12mag stars are mising in M67 and the 12.1 stars were not resolvable) - I assume 11.9
130mm 11.8
120mm 11.7
110mm 11.6
100mm 11.5
90mm 11,3
80mm 11.2
70mm 11.1
60mm 11
50mm 10.8
40mm 10.4
The smaller apertures below 60mm are somewhat difficult, as the star pattern changes due to the "loss" of the fainter stars so I will next time make a star chart with only the stars below +11mag.
This result seems very plausible and means that I have so far overestimated the magnitude loss due to light pollution by about 0.5mag for 140mm aperture. Interestingly also that the magnitude loss is clearly going down with aperture as was to be expected.
Wilfried

#28 WRAK

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Posted 13 May 2013 - 04:09 PM

M67 is meanwhile rather low now for me and other observers in the northern hemisphere (last report was a +12.4mag TML for 152mm aperture and NEML of +4mag from Roberto) - may be I can have a last look at it with my 235mm SCT around dusk if the meanwhile again rotten weather allows.
Next good targets will be NGC6823 in Vul and NGC6910/NGC7031 in Cyg in September (Cotts: Thank you for suggesting these). I will prepare star maps with hopefully existing AAVSO magnitude values for these open clusters.
Wilfried

#29 WRAK

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Posted 15 May 2013 - 02:11 AM

Tried yesterday a bit late in the evening with the 235mm SCT. Despite a for my location rather good NEML of +3.45mag I got only a slightly better image than last time with the 140mm refractor. Bad seeing and altitude below 25° seems to have an erasing effect on fainter stars.
Wilfried






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