Delta Velorum - non-observed

American Association of Variable Star Observers (AAVSO)
Thu, 02/18/2021 - 17:22

I am a begginer variable star observer from the Southern Hemisphere (but with experience in astronomy) and, when I was looking for VS to observe, I saw that Del Vel has almost no observations. Thus, there is no graph for when the eclipses occur.

VSX data: mag range of 1.95 - 2.43 V, period  of 45.15 days and 1.3% (0.587 days) eclipse duration

It doesn't have data about how the magnitude varies in the visual spectrum, althought I know it is a bright star (already saw it at naked eye).

Does it vary in the visual spectum, or there simply is no data enough to determine this? Could I collect this information visually, or is this waste of time?

American Association of Variable Star Observers (AAVSO)
Del Vel-Poor Visual Choice

Frankly, this is a poor choice for visual observing... the change in magnitude is quite small and there are not really suitable comparison stars available within any available field of view chart size for visual observers.

Have you looked at the following, as there are a number of suitable targets for new visual observers in the Southern Hemisphere with lots of hints about observing.

     11-Star Training Tutorial for the Southern Hemisphere:

Welcome to the AAVSO and have fun with your new journey in Astronomy.

Tim Crawford, Sequence Team

American Association of Variable Star Observers (AAVSO)
11-Star Tutorial - Measuring Brightness

Thanks for recommending this tutorial! I've read the tutorial and the visual observation manual, but I ended up with a question about estimating the brightness of the stars that I couldn't find the answer in the internet.

The AAVSO manual suggests picking the comp stars and simply guess the variable's brightness. I have seen that some people use methods, as the Pogson Step method and the Fractional mathod, in order to obtain more precise results.

Although, the magnitude scale is a logarithimic scale, not a linear scale! So how can one assume that each magnitude fraction/tenth of magnitude will have the same intervall of brightness variation?

I mean, when a star is 2nd magitude, the half of its brightnes is NOT a star of 4th magnitude! So, I cannot digest how dividing the magnitude difference equally would end up with equal brightness intervals.

If I was unclear with my question, please tell me and I will try to rewrite it in other way.




American Association of Variable Star Observers (AAVSO)
Measuring Brightness


The AAVSO manual suggests picking the comp stars and simply guess the variable's brightness.

Well, not exactly, your comment is a bit of a simplification of the actual process... yes you have to make a guess but the guess is a judgement based upon what  differences your eye notices when comparing close in magnitude comps with the target.  Please re-read paragraph 4 on page 13 of the visual manual and then re-study the page 14 Interpolation Exercises.

Frankly, once you actually take a chart outside for one of the 11 tutorial targets you will find the process to be less complex than it might appear without benefit of actually making an observation.

FYI, it has been my observation and experience that beginning visual observers observations can vary ~ .5 magnitude from more experienced observers and that some experienced observers are able to make a visual observation within ~.1 magnitude, especially if the fov provides suitable comparison stars.

Again, my best advise is to take a chart outside and start the learning curve... it is not really that difficult and is really rewarding once you actually make some observations.

Also, I have asked a more experienced visual observer (my forte was CCD observing) to also remark on your last.

By the way, you might also consider the AAVSO Mentor program (for members) and take advantage as you could then have one on one mentoring by an experienced visual observer:

Per Ardua Ad Astra


American Association of Variable Star Observers (AAVSO)
Linear approximation works well for small magnitude differences

Hi Vitor,

You are correct that the magnitude scale is non-linear. However, linear approximation works just fine for small magnitude differences. When magnitude differences are less than half a magnitude or so, the results will be very accurate. Always use at least two comparison stars. One should be a little brighter, the other a little fainter. Then use linear interpolation to estimate the variable star's brightness.

For example, if you observe a variable star to be half-way in brightness between a magnitude 1.7 star and a magnitude 2.3 star, then magnitude 2.0 would be a perfectly good estimate.

With practice, you should be able to estimate a star's brightness within +/- 0.1 magnitude. That's an intensity difference of approximately +/-10%. Everyone sees things a little differently. The beauty of having many observers is that the data average can produce a result that has an error much smaller than 0.1 magnitude.

Hope this helps to explain a little more. Good success beginning your observations of variable stars! Best, Andy