During the last SSP-Talk Joyce A. Guzik asked about the uncertainty in our observations. Last year I already noticed there were several nights that at least two observers measured alf Cyg within 0.3 day. I decided to download our data from the AID. From this data I identified 25 nights in which two observers and 2 nights in which three observers (night 7 and 9) measured alf Cyg. I’ve plotted these measurements with their uncertainty in the graph below.
On most nights our observations agreed on the 1 sigma level, but there are exceptions. Most exceptions agree on the 2 sigma level, so I will ignore these cases and go a bit deeper into those cases that deviate substantially.
Night 6: Both observers report 0.001 uncertainty, but with a difference of 0.022 magnitudes. These observations was 0.18 days apart. Is this long enough to show a significant fading of alf Cyg?
Night 16: A difference of 0.009 magnitudes with observations 0.26 days apart. Is this long enough to show a significant fading of alf Cyg?
Night 20: A difference of 0.024 magnitudes with observations only 0.044 days (about 1hour) apart. Both observers reported issues (contrails and thin smoke in high atmosphere), so the problem probably lies here.
Night 26: A difference of 0.017 with observations 0.036 days (about 1 hour) apart. One of the observers reported light pollution, so this might be the cause of the ‘discrepant’ data point.
So only 4 of the 27 nights have issues, with 2 that can be attributed to the atmospheric conditions. It is really important to report these conditions, so later researchers can exclude observations when something seems off.
It is good to see most multiple observations by multiple observers agree within 0.01 magnitude, often much better than this. This shows the power of well reduced PEP data.
I have to get one more thing of my chest: Please consider to determine K_V every clear night, instead of using an estimated K_V. I’ve noticed that the measured K_V doesn’t always agree with the estimated value. This may cause a huge difference in the calculated magnitude. In one case I had a difference of 0.011 magnitudes between the calculation using the measured K_V and the one using estimated K_V (with the same data). Last year my average measured K_V was 0.28, with values ranging between 0.14 and 0.41 (yeah, the day-to-day atmospheric conditions vary a lot in the Netherlands). With the Hardie method K_V is very easy to determine. It takes less that 15 minutes and it makes your reduction so much more valuable.
