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Estimating red variables

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MDAV's picture
Estimating red variables

I’ll start the first observing technique topic on this forum- “American” v “European” method of visually estimating red variables. I am not setup for photometry so I am currently doing purelyvisual.


The “American Method” involves taking quick glimpses of the stars- which is the natural technique for most people in the states.


Te “European Method” involves defocusing the images to eliminate the color contrast.


For most of my estimates I use the “American” method- especially when observing fainter stars (my faintest observation being a 14.8 mag comparison star for R CrB on chart 1157gxy). 


But with an intensely red star such as R Leo I find my eye doing exactly what I don’t want to do-being drawn to the star by the intense hue and staying there. The amount of scatter in my estimates  go up -especially near max. 


Consequently I  use the European method on these stars.  I find that I have less scatter using this technique when there is a strong color contrast.


My questionwould be:


What techniques do others use?



Estimating Red Variables

I must admit I have not thought in terms of American and European methods before . I also use both methods and I tend to use the American method of quick glimpses  for most stars and the European method of defocusing the stars for the brighter red variables - similar to your technique MDAV .

Let us hear from other observers

MDAV's picture
Estimating red variables

AAP:I heard these techniques referred to as "American" and "European" some years ago but I don't remember the context. I'm curious as to the amount of scatter other observers have using these methods. For my own I usually take the mean of several estimates. I have noticed that my scatter is less on brighter stars using the de-focusing method but the opposite on dimmer stars. Dave M.

SXN's picture
Visual methods

I use both methods. I only find color to be an issue when the star is bright enough to grab my attention color-wise, so I tend to use the defocused method on stars brighter than 10th magnitude.

I also observe most stars brighter than 9th magnitude in my finder scope, because they are far too bright for my 12" SCT. Once I have made the estimate I confess to having a good stare at some of the redder ones, just because their color is so remarkable.

Estimating Red Variables

I use the “European Method” most of the time.  I'm just starting to do more visual observing after only doing ccd photometry for the last few years. I've started experimenting with a variable polarizing filter. Its a neutral grey and takes some of the color out of the very red stars and can dim them to a level that's easier to estimate.
It's still a work in progress.

hhu's picture
I always use the european

I always use the european method.

Maybe it's because i'm from europe;)

Clear skies, Hubert

Method for red stars

I used the european method most of the time, when I did visual estimates rather than using CCDs. One thing to be considered when defocusing stars is that red and yellow stars generally appear dimmer than white ones. I therefore studied a method of "calibrating the eye" by comparing several stars of known magintudes and then used a correction coefficient to calibrate my visual observing. I measured this effect to be as high as 0.6 mag (yellow and red star disks appear dimmer by 0.6 mag of white star disks even if they have the same brightness).

SMIK's picture
What about averted vision?

I'm new to all this, but I'm happy to be corrected if I goofed.

I went to R LEP last night and was blown away by how deeply red it is. It was truly mesmerizing - I just wanted to keep staring at it. It was easy to see that it was dimmer than the 7.4 comp on the chart but R LEP was clearly all about R LEP.

So I tried averted vision and that made taking quick glances easier and it seemed to me that its redness wasn't interfering. Was I wrong? Will this approach work only in a certain magnitude range?

MDAV's picture
R Lep

Hello Mike:

Welcome aboard.  Anytime a star is bright enough to show color extra caution is advised. Ideally-which is rarely the case- the comp stars should be comparable in color to the variable. The sequence team people are constantly trying to improve this-so keep your charts updated. In addition the longer you look at a red star the brighter it becomes. So looking away and taking just glances is an appropriate technique. Make sure however that you use the same technique on both the variable and the comp stars.

Depending on what equipment ypou use it may be advisable to go to smaller aperture to lessen the effects. For example-I will routinely use the finder on stars like R Leo. I also look away , rest my eyes, and make another estimate. And do that several times. But don't outsmart yourself or anticipate what you will see- its a temptation. Just take what you see. As you get practice you will get better. The other technique is to rack the star out-for both the comp and variable to eliminate as much of the color as possible.

Occasionally-you will make an estimate that is way off what most people have recorded. You will be tempted to not submit the observation. Unless you can clearly identify what your error was- wrong star etc.- that temptation should be resisted and the observation submitted anyway. Sometimes I have though my estimates were off . But as other observer data was submitted and the gaps filled in I found my observation was not off after all.

Incidentally R Lep is named Hind's Crimson Variable. It has undergone enough dredge-up events to bring up lots of carbon-which of course is the reason for the intense red tinge- that and the fact that these stars are very large and cool anyway.

Have fun and take pride- there are only a bit over a thousand people worldwide that submitted visual observations in 2010 so you are in a small and select group.


Dave M (MDAV)

SXN's picture
That was excellent...period

I was scanning the forums to see if I needed to pop in and speak up, and i have to tell ya Dave, you made anything I would have said entirely redundant. You covered it all.

Kudos, Man.

Mike Simonsen (SXN)

KRS's picture
What about averted vision

Averted vision is the best technique for red stars.  The rods of the eye are not color sensitive. 

1. Use the smallest aperture possible for the observation.  Being close to the limit of your scope makes your eyes more sensitive to differences in brightness.

2. Defocussing is useful at the limit, but not for really bright stars,

lmk's picture
Visual methods

A lot of good posts here. Just to summarize my methods - I use defocus a lot. Its much easier to tell small differences in brightness with large blobs than a miniscule point. Especially with my Newtonian, I can see how prominent the central obstruction appears between the two stars being compared. Also, the amount of defocus can be adjusted to bring practically any star within the optimal brghtness range.

Sometimes I even estimate 7 or 8th magnitude stars with my 20" under very low power and extreme defocus this way! Works quite well if you dont have binos handy.

For stars within a magnitude of my limit, usually I just use them in focus to get the best contrast and viewing. If you are a few tenths above your limit, its even easier to tell differences in brightness. Thats at the tail end of your retinal response curve, where small differences in brightness are very apparent.

BTW, where does the "European" method name come from? I thought the defocus techniques came from the comet observing methods, like Sidgwick and Morris?

Mike LMK

BRJ's picture
Source of the European Method


BTW, where does the "European" method name come from? I thought the defocus techniques came from the comet observing methods, like Sidgwick and Morris?

Mike LMK


The method being termed the "European method" is, to my knowledge, derived from the practices of early German comet and VS observers like Graff and Beyer way back in the teens and twenties of the last century. 

The so-called  "Morris method" is simply a minor variation of the technique utilized in the European (or Beyer's) method, having been purposed by C.S.Morris in the 1980's.

J.Bortle   (BRJ)

PYG's picture
Well if Sidgwick did

Well if Sidgwick did introduce the 'European' method it should be called the 'English' method, because we aint European over here!  A common mistake made by a lot of people.

For the very few red stars I do observe, I use defocus and quick glimpse - but reduced aperture is the best way.  One of the reasons I always use a decent sized finder on the big scope, and have an aperture stop for the smaller 22cm.

Gary (PYG)

pox's picture
That's debatable Gary! They

That's debatable Gary! They stock Dutch-language newspapers in my local village shop, and East Norfolk is full of 'vans' and 'van der's'.

Seriously, I'd never heard about these terms. Surely one needs to be consistent. I never defocus on estimates. If a star is so bright that you feel you should defocus, then simply don't record it. Of course, that's not the same as saying "don't look at it". S Cep goes down as my all-time deep red attraction. PQ nearby is a close runner though.

BBI's picture
I used to use the

I used to use the “European Method”, until I estimated a very red star with a binocular to be very faint. Afterwards I noticed it was visible with the naked eye, and much brighter...

Now I take quick glimpses, litt out of focus. I also noticed that I estimated red stars slightly brigher using a bigger instrument. Maybe because the colour is more prominent using a big instrument? So I try to use a small binocular (8x40) for the bright stars (until mag.8).

TYS's picture
Why I use the European Method.

I use the European method and defocuse the variable to be observed. I've found there is a big difference in the visual brightness of red variables as they look much brighter when focused. I feel there is large ammounts of scatter with bright red variables because a lot of observers don't defocuse their views so they give a much magnitude brighter estimate then the variable really is.

Pete B
Visual Out of Focus versa V Band

As a relatively new observer I would like to ask, does the ‘defocusing method’ give an estimate that is much fainter than the variable really is ? 

When I look at light curves of Mira's and SRs’ with both visual estimates and V Band measurements plotted, I have noticed that in general most of the visual estimates are in a range of up to about 0.5 Mag below the V Band ones. 

I have tried both methods and as mentioned noticed that defocusing causes the estimate to be a lot lower. However have found the “quick glance” method for me produces estimates that are compatible with reported V Band measurements.

BRJ's picture
Methodolgy vs. Results

Pete, it kinda depends on just what you want to accept as the "actual" brightness" of the variable. Like it, or not, CCD or PEP "V' magnitudes are simply not an exact match to what the human eye sees - never have been, never will be, in spite of what some might attempt to claim. Quality visual magnitudes are just as correct as those made with a CCD, but they are in somewhat differing systems. This is why there is an on-going attempt at HQ to find a means of making the two systems more compatible, ultimately allowing the two lightcurves to be blended together.

Making matters worse, the difference between "V" and eyeball is different for different variables, particularly the red ones and the spectral oddballs, the electric devices responding to certain spectral aspects of the variable's light, the human eye apparently less so. Thus, it is not unusual to see visual estimates paralleling the CCD V lightcurve by some tenths, even up to a magnitude, and usually offset to the fainter side of V.

Addressing the question of comparing using in-focus vs. extra-focal images of the stars, 50 years of VSO has indicated to me repeatedly that the extra-focal brightness determination is more likely to result in the more accurate determination, especially with red variables. In addition and never to be neglected is the problem of employing too much aperture for the brightness of a given star. This, as well, can serve to distort the estimate, producing an excessively bright figure (and even more so if the estimate is made by the in-focus method). Always try to use an aperture appropriate to the brightness of the variable.

J.Bortle   (BRJ)


MDAV's picture
Visual Ouf of Focus V band


  Since you are performing interpolation measurements the de-focusing method does not necessarily give you a "Fainter" estimate per se. You are using the established sequence to assign the numbers. It may appear to be that way however for a couple of reasons.

For our LPVs we have a natural -"Red Means Caution" 

   Probably the best known pitfall in overestimating the visual magnitude of red stars is inherent to the physiology of the eye. Called the Purkinje effect- it causes a red star to appear brighter the longer you look at it. This could well be one factor in thinking de-focusing gives you dimmer estimates. 

   Another potential source is the difficulty in interpolating magnitudes with a large apparent color difference between the variable and the comparison. I can't say I estimate the stars as brighter but my scatter and difficulty goes way up. It gets real easy to fool yourself. This is the primary reason for using the defocusing method or smaller aperture-eliminating as much of the color difference as possible.

   When you use the de-focusing method you are no longer dealing with a point source but an extended image- so the apparent surface brighness will decrease. This does have the effect of making stars appear dimmer. They are- but the relative brighness doesn't. As you have no doubt seen using this method there is a limit to how far you can go with de-focusing. As John pointed out you also need to use the appropriate aperture.



puj's picture
Estimating red LPV

I use the european method and  specially when I have doubts about what interval  of comparison stars to use. The real problem is when you fail placing correctly the star between the two comparison stars selected. To overcome this problem is very useful the european method. By doing this the possible mistake estimating the variable is going to be small, but if you go out from the right interval, you can be nearly one magnitude out of the real value 

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