How do you get an accurate magnitude estimate visually?

Hi Tony,I'm glad you are observing Eps Aur. I love Maine. I spent a week on Hog Island at an Audubon Educators Camp 2 summers ago.First of all, from your dark skies you shouldn't even need binoculars to observe Eps Aur or its comparison stars. However, if you are using binoculars, I find it very useful to defocus the star images a bit when you make your magnitude estimate. I do this all the time with variable star observing. It gets rid of star color, which can play games on your eyes, especially red stars. I don't think any of the stars we are talking about are red, but they are bright, especially in binoculars. Just throw them all out of focus a bit, but not to much, when you make your observation, but not when finding the field of view.Sounds to me like you are right in the ball park as far as your observations go. Sometimes as a new observer, one can doubt if his/her observations are very accurate. But your's sound right on. So, have at it, you are doing a fine job.Chris StephanRobert Clyde ObservatorySebring, Florida USA

I've been struggling too. We have a large range between the 3.2 and 3.8 comparison stars which makes it extra challenging. Ideally, we prefer to have comparison stars spaced about 0.2 mags apart. But mother nature rarely gives us star patterns that allow it. :) It's easier with fainter stars since there are so many of them. Also, remember you can submit estimates at an accuracy of greater than 0.1. For example, in my last observation I struggled between calling it a 3.4 or 3.5. So I submitted it as a 3.45. That does not mean I think I have 0.05 precision eyeballs. It just means that 3.45 is the middle of the scatter I felt like I had at the time.

Thanks Chris for the idea on the binoculars...I will try that. Sometimes I can look at those stars for a few minutes and one second it seems brighter than the next second. I think after a while your eyes and mind start playing tricks on you, so I usually just try to look quickly and take my first impression.

I did the same thing for last night's observation. I ended up putting in 3.55. I thought that EA was just a bit closer to 38 than 32.

I just got done looking at the three and find epsilon closer to 38 than 32 at 3.6, Thanks for your question and the replies. 11/20/2009, 12:30-40am, PDT.

I've been pondering this for a while. As a member of the British Astronomical Association, I am used to their methodology, which is slightly different to this. Let me explain. Using the 'fractional' method, we couldn't actually get this result without effectively dividing the magnitude range between 3.2 and 3.8 into 12 steps and then deciding that 32(5)V(7)38 was our estimate. This realistically would not happen. In any case, the resulting value of 3.45 would be rounded to 3.5, i.e. the nearest 0.1 of a mag. More likely we would record either 32(1)V(2)38, giving V = mag 3.4, or 32(1)V(1)38, giving V = mag 3.5. Either of these would be recorded with an associated accuracy 'class'; "A rough indication of the reliability of the magnitude estimate. A good estimate is indicated by 1, an average one by 2, and a poor one by 3." [ http://www.britastro.org/vss/ ]Class 1 is usually taken to be +/- 0.1 mag, class 2 to be +/- 0.2 mag, and class 3 as just about better than no observation at all!So, either of our possible estimates (3.4 or 3.5) would be +/- 0.1 mag, which would include the estimate of mag 3.45 within the range, although it would not be the central value.Some of the visual data does, on the face of it, seem to be recorded to a precision of +/- 0.01 mag. Is this realistic?Is there any way of recording the estimated accuracy of our observations? David Conner.

Hi David,I would have a hard time getting visual accuracy down to hundreths of a magnitude. I just do not think the human eye is capable. This method you share seems a bit complicated to me, but I admit I have never used it. Chris StephanRobert Clude ObservatorySebring, Florida USA

Hi Chris,It sounds complicated, but it isn't in practice. Here are my observations of eps Aur from my own log, in BAAVSS format as submitted to the BAAVSS.I think the only real difference between the methods (apart from including the actual estimate) is the inclusion of the class (='cl') which is an estimate of the accuracy of the observation. Star; epsilon Aurigae Times in U.T. 2450000.000 plus Date h m UT Dec JD Dec Estimate Mag Cl Seq. 2-Aug-2009 00 20 2.014 5045.514 B(1)V(1)C 3.1 1 316.01 21-Aug-2009 00 36 21.025 5064.525 V(=)B 2.9 1 316.01 24-Aug-2009 01 20 24.056 5067.556 B(1)V(2)C 3.0 2 316.01 25-Aug-2009 00 45 25.031 5068.531 B(1)V(2)C 3.0 1 316.01 1-Sep-2009 23 50 1.993 5076.493 B(1)V(2)C 3.0 1 316.01 12-Sep-2009 23 50 12.993 5087.493 V(=)C 3.2 1 316.01 27-Sep-2009 02 04 27.086 5101.586 C(1)V(3)D 3.4 1 316.01 7-Oct-2009 23 50 7.993 5112.493 32(1)V(1)38 3.5 1 AAVSO 16-Oct-2009 22 00 16.917 5121.417 32(1)V(1)38 3.5 1 AAVSO 1-Nov-2009 22 40 1.944 5137.444 32(2)V(1)38 3.6 1 AAVSO 17-Nov-2009 00 20 17.014 5152.514 32(2)V(1)38 3.6 1 AAVSO David.

That looked OK in the 'preview' window, but the formatting got lost when posted. Never mind, I think the idea is there.David.

I've read somewhere that in the old days, one method to visually assign magnitudes involved a telescope (or binoculars) where you could easily diminish the aperture (or maybe use filters with diminishing transmission). The idea was to use the aperture that made the star vanish (brightness below the observer's individual detection threshold). For differential visual photometry, you could reduce the aperture until either the variable or the comparison star "vanishes". It sounds like a clever idea to me and I wonder whether this technique still has some merit today.CSHBE

This is a new one to me. I haven't heard of it before, but that does not mean it might not work. If you try this, share your results with us.Chris StephanRobert Clyde ObservatorySebring, Florida USA

The basic idea goes back to the times of Herschel and Norman Pogson, the father of the "modern" logarithmic magnitude scale. http://adsabs.harvard.edu/full/1968ASPL...10..145JI don't think I'll try this, I'm more into DSLR photometry. Still I think it might have some use.CSHBE

To be more specific, what comes to mind when reading about these old-days methods is this: Picture it: You have a filter wheel (perhaps made from laminated cardboard, mass produced) with a set of (say) 12 "grey" filters, where transmission varies from one filter to the next by a factor corresponding to (say) 0.1 mag (about 9 % IIRC). This is for "fine adjustment". You can also put a filter from a set of 1.0 mag spaced filters in a fixed position. You look at a comparison star (eyeball/binocular/telescope..whatever) and turn the filter wheel until you just can't see the star anymore. You do the same for the variable. Start at a random position of the wheel to avoid bias. If the difference in mag of the two stars is not so huge, you will not have to change the "fixed filter" (the act of changing it may alter your dark adaptation). An alternative design would involve two sandwitched filter wheels in an obvious configuration. The difference in the combined filter strengths would hint at the mag difference V-C. Add to this the catalog mag of comp star C and get V. Maybe the Mark 1 eyeball team wants to look at this or other, more elaborate "visual, but assisted" methods ?? Just an idea Heinz

Hi Tony: I have a couple of suggestions for you-especially if you are new to this type of thing. Doubting yourself initially is normal but don't let it lead you into trying to anticipate what the star should be doing. As long as you are diligent with your technique you will be fine and your observations and confidence will improve with experience. If you do have doubts look over at the quick look section on the AAVSO website to see what others have been seeing at http://www.aavso.org/data/ql/ But don't let that keep you from submitting your observations. I have often had observations I thought were discrepant but as time goes on and other observers fill in the gaps they turned out not to be. There is nothing unusual in seeing scatter in the observations. Another thing you can do is to look away, reset your eyes and do a new observation from scratch. Try a couple of other stars as well with different types of variability. I initially cut my teeth (or eyes) on Algol, Del Cep, and R Leo. One of the advantages of doing this is that it helped verify technique. Try a red star too to get familiar with the Purkinje effect. R Lep is currently at the bright end of the cycle and R Leo is currently on the dim end. Personally I have trouble with red stars at the bright end. One technique is to use the European method of de-focussing the star image Good luck and good hunting. Dave M.

Iam also concerned about giving inaccurate results. While waiting for a properly clear sky, I have tried out the HOAFun program which has a test for gauging your accuracy at Variable Star estimates...Igot a 36% my first time, which kinda scares me. I really think it just takes practice, but it's hard to know if you're off, and by how much. Just keep trying. I'm new to most of this, but I find it rather exciting to be involved in collecting this data. Still, it will probably be a while before I'm confident enough to submit real results. I just found a Log Book plugin for Stellarium. I'm not sure if it will let me record estimated brightness (Idon't know why it wouldn't), but I'm going to download it and try recording my observations to check against others. Maybe this will build my confidence, as well as put things in perspective.... (EDIT: Log Book plugin mention)

Submit those observations, you're probably closer than you think on most observations. If you've kept records of your observations, compare them to those submitted to the AAVSO using the recent observations 'quick look' module on the AAVSO site, http://www.aavso.org/data/ql/. Make sure you set the right date and right star, you'll be able to seefellow 10 star members estimates as well as standard AAVSO estimates (you'll see 10 star under the chart section, that means it's one of us). See how close you are to the estimates input, if you're off then no worries but you are probably closer than you think. Don't check the quick look before doing observations however, it will impart a bias in your estimates. Also, if you've not already done so, ready Mike Simonsen's Rules for Variable Star Observing. http://www.citizensky.org/forum/avoiding-bias-simonsens-rules-variable-star-observingIt's quite interesting and an excellent way to learn how to observe.

I'm a newbie to this myself, if Ican pick it up anyone can!:) Hope that helps!!