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Astronomy with an online telescope

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Picture of Paul Mckay

Paul Mckay Post 1

29 Dec 2020, 13:38

Flip Function

Hello Alan and Jo

Although I have completed the Astronomy with Online Telescope course, I have requested more variable star (EB1) images for plotting on the 'communal' chart.  I am interested in how the Flip function computes the data points and translates them into a single brightness v time plot. I have done some research but it does look very mathematical so would be interested in a layman's explanation.

It seems to gather data points of similar brightness across a narrow range of brightness and asign the 'average' to a single time value. When this is repeated across the full brightness range a cyclic pattern emerges. More points from many periodic cycles gives improved accuracy because random errors become a small proportion of the data set. 

It certainly yields impressive results as long as data points cover the whole of the cycle, particularly at maxima and minima, where the brightness/time function is sinusoidal/non-linear.

Absolutely fascinationg stuff.


Picture of Alan Cayless

Alan Cayless Post 2 (unread) in reply to 1

4 Jan 2021, 17:08 Edited by the author on 4 Jan 2021, 17:09

Hi Paul;

Thanks for adding your data points to the group results - it is great to see the curves building up !

Your description of the folding is correct.  In the normal view of the light curve the data points are plotted against the date and time of observation, but this makes the curve very spread out, covering many oscillations of the variable star.  The "Fold data" function combines these into a single period, overlaying the data points to make an average curve for a single orbit of the stars.  It's a bit like plotting phases of the Moon in terms of days after new Moon, or average daily temperatures from different years in terms of days after January first.  This resulting in several cycles plotted on top of each other, but in phase, to give a more accurate picture of the shape of the light curve.

Of course, to do this we need to know the period of the variable star in the first place, so a number of observations are needed before we can start folding.



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