# Talk:Uncertainty parameter

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Astronomy C‑class Low‑importance

## Adding a section on Formula - calculation

Maybe we should add a section on Formula - calculation

The U uncertainty parameter(referred to as the “Orbit Condition Code” by JPL) is logarithmic scale where 0 indicates a well-determined orbit and 9 is a poorly-determined orbit. RUNOFF is the in-orbit longitude runoff in seconds of arc per decade.

RUNOFF = ( dT  • e + 10/P  • dP )  • ko/P 3600  • 3

𝑑𝜏 = uncertainty in the perihelion time (in days)

𝑒 = eccentricity

P = orbital period (in years)

dP = uncertainty in the orbital period (in days)

ko = 180/π  • 0.01720209895 , the Gaussian constant in degrees

3600 converts to seconds of arc

3 is use as empirical factor to make the formal errors more closely model reality

U = INT(ln(RUNOFF)/CO)+1, (0U9)

CO = ln(648000)/9

comment there is some possible dimensional inconsistency here as days per year are being added to dimension days (d Tau). e, the eccentricity of orbit is by definition dimensionless. Possibly there is a dimension built into the 10 but that is far from clear. It is worth noting that e is not defined in the base page, only on this "talk page"TimFid (talk) 06:32, 17 June 2017 (UTC)

Bayoustarwatch (talk) 04:56, 28 February 2016 (UTC)

Please explain what each of these terms mean, in language understandable to non-astronomers. (I only took one astronomy course in university; I have no idea what you're talking about here.) I've put the "too technical" tag on the section in the main page because of the lack of explanation on this page. --Rob Kelk 16:27, 1 May 2016 (UTC)

## Orbits Vs. "Future orbital position" Vs. "future motion "

There is "some" debate over if it should be "The U value should not be used as a predictor for the uncertainty in the future orbits of near-Earth asteroids." or "The U value should not be used as a predictor for the uncertainty in the future motion of near-Earth asteroids" I think could be stated "The U value should not be used as a predictor for the uncertainty in the future orbital position of a near-Earth asteroids." some feedback would be niceBayoustarwatch (talk) 22:33, 6 March 2016 (UTC)

"Motion" is certainly better, and what the source has. But I still think "orbit" is more precise and a perfectly good way to paraphrase the source. --JorisvS (talk) 22:50, 6 March 2016 (UTC)

## Uncertainty if the parameter were over 9

I don't understand why you say that the uncertainty would be 40° if the parameter were over 9. The formula is:

${\displaystyle U=\min \left(9,\max \left(0,\left\lfloor 9\cdot {\frac {\ln r}{\ln 648{,}000}}\right\rfloor +1\right)\right)}$

So, if we didn't have the "min", the value would jump from 9 to 10 when ln r hits 648 000. That corresponds to 180°. Eric Kvaalen (talk) 14:03, 20 September 2016 (UTC)

Perhaps I had phrased it wrong: I wasn't necessarily referring to the integer value of 10, but simply any value over 9, or 9.1, 9.01, or 9.001. If I am doing my calculations correctly, this value would be 40 degrees per decade? exoplanetaryscience (talk) 03:50, 22 September 2016 (UTC)

But fractional numbers are not used at all. The symbol ${\displaystyle \lfloor \,\rfloor }$ in the formula means the "floor function". It rounds down to an integer. So the next value after 9 is 10, and 10 corresponds to 180°. Eric Kvaalen (talk) 15:39, 8 October 2016 (UTC)