The data of orb.js is different from the data of other web calculators.

[alexandergrishin]

Hi!
I tested orb.js web tool and it provided data that different from such web calculators.
Maybe it will be helpful for you.

Inputs
Date
local: 2020-03-13 20:18:07
UTC: 2020-03-13 18:18:07

Selected planet
Mercury

Latitude
35.6833453
Longitude
139.7333

Here are links on calculators from screen:

• Clearskytonight
• Cosinekitty
• Casio

[lizard-isana]

Hi!
Thank you for your feedback. It's quite helpful!

It results from the difference between the "astronomical position" and "apparent position". Orb.js returns the "astronomical position" of planets which means that it does not include the light-time correction and effects of nutation.

JPL HORIZONS shows both positions at 2020-03-13 18:18:07 UTC from the center of the Earth:
Astronomical position: 22h 01m 59.50s, -11d 21m 11.4s
Apparent position: 22h 03m 01.97s, -11d 15m 31.2s

However, as you know, it is uncommon. I'm considering the script returns "apparent position" by default.

[sebagr]

How would one go to convert from astronomical position to apparent position? Is it possible to do with the current script?

I'm particularly interest in comet and asteroid orbits. I can see in the code there are several references to nutation (for the Sun, the Moon, in Orb.Time, Orb.Obliquity and Orb.NutationAndObliquity), but I'm not sure if these affect comet orbits (Orb.Kepler) in any way. Thanks!