TiffsAndAstro:
I'm I correct in thinking the (1.8) is the RMS error ? If so, what is the 0.3 ?
Nick Grundy:
@TiffsAndAstro if you get stuck on something, I actually upload screenshots to Chatgpt and find some surprisingly accurate answers. It tends to fail with highly specific or contextual questions though.
posting your initial question, this was the response. The forum will likely get you the best possible answer, but if you can't wait...
****chatgpt's reply****
In the scenario you described using N.I.N.A. (Nighttime Imaging 'N' Astronomy) with PHD2 for autoguiding, the notation "0.3 (1.8)" likely represents two specific measurements related to the performance of your guiding system:
- 0.3: This is usually the current error in arc seconds. It indicates the immediate, real-time deviation or error from the desired tracking position of your telescope. This value can fluctuate quickly depending on many factors like atmospheric conditions, mechanical stability, etc.
- (1.8): This number indeed represents the RMS (Root Mean Square) error, also in arc seconds. The RMS error is a statistical measure that quantifies the average deviation of the guide star's position from where it is supposed to be over a period of time. It's a more stable measurement compared to the current error and gives you an idea of the overall guiding accuracy and stability during your imaging session.
Thus, in your example, "0.3" indicates the current error is quite low at the moment you checked it, suggesting good immediate tracking performance, while "1.8" as the RMS error suggests that over time, the average error has been a bit higher, which might prompt adjustments in your setup or conditions for improved long-term accuracy."
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John Hayes:
I don't know Nina but I know math. Most guiding software reports errors in both PV and rms. The smaller number is typically the rms and the larger number is typically the peak to valley (PV) of the guide error. For randomly distributed values, the rms typically ranges from 1/4 to 1/6 of the PV. Just be sure that you know the units. It is common to be able to express the errors in units of either pixels or arc-seconds. Arc-seconds are the most useful when comparing the performance of your system with other systems and when you report numbers here, arc-seconds are generally the most useful units to use.
John
Arun H:TiffsAndAstro:
I'm I correct in thinking the (1.8) is the RMS error ? If so, what is the 0.3 ?
The 0.3 is probably the error in guide camera pixels, and the 1.8 would be the error in arc seconds, assuming you have entered your guide scope focal length and guide camera pixel size correctly. The 1.8 is the more important number, as John has stated, since this allows you to directly determine how this error would impact your subs. As an example, if your image scale is 1.4"/pixel for your main scope and camera, the 1.8" error tells you that your errors, on average, are not restricted to within a single pixel, which will result in distorted stars and loss of edge resolution of whatever it is you are trying ti image.
Brian Puhl:
With all due respect, please don't use ChatGPT for Astro. It's so incredibly clueless 95% of the time.
Brian Puhl:
In NINA, the first number is the guide error in PIXELS. The second number is ARCSECONDS. The clue is the " which means seconds.
The drop down menu is specifically for the graph display. Generally speaking this should always be in arc seconds, but if you use an OAG and have the same image scale for your guider AND imaging camera, then it can be useful.