Contents
About osculating elements
How to add your own objects
Data Formats
Examples
New comets and asteroids, courtesy Mark Allision
About osculating elements
Comets and asteroids follow orbits that are much more complex than planets. To remain compact and fast, 2sky computes these orbits as if they were simple ellipses or hyperbolas, using osculating orbital elements that describe the motion of the orbit at a specific moment, or epoch, in time. The computed positions are very accurate near the epoch, but diverge wildly at times far from the epoch. Comets will stop displaying when they're out of epoch, though asteroids won't. 2sky comes with two small databases of the more visible comets and asteroids, which are updated with new objects and the latest epochs with every new release.
How to add objects to 2sky
If you are an expert, or just feeling experimental, you may add your own favorite comets and asteroids of any epoch to 2sky by following these steps:
- Get the osculating elements online from the MPC's comet and asteroid pages, or JPL's ephemeris generator (check the "Include body information page" checkbox at the bottom).
- Create a new memo in your Palm Desktop application.
- Copy and paste the data into it in the formats below. (Examples)
- Close Palm Desktop and hotsync.
- Open 2sky, open its Options menu, and choose Import Comets or Import Asteroids.
- If you get an error message, check your work. If you got this far, you're definitely smart enough to figure it out.
Data Formats
Everything is case-insensitive and you may put any number of spaces or carriage returns between numbers. There should be no commas. All orbital elements (including epochs and times) must have decimal points. The name of each object belongs immediately after its orbital elements. 2sky reads only the first memo that begins with either "2sky asteroids" or "2sky comets", followed by the objects, each on a new line in one of these two formats:
Epoch M a e Peri Node Inclination H G [Asteroid name]
Epoch T q e Peri Node Inclination g k [Comet name]
Where:
- T = time of perihelion passage in Julian Days
- M = mean anomaly at the epoch in degrees
- q = perihelion distance in Astronomical Units
- a = semimajor axis in Astronomical Units
- e = eccentricity
- Peri = argument of perihelion in degrees
- Node = longitude of the ascending node in degrees
- g, H = absolute magnitude
- k, G = slope parameter
Examples
Here's the text from the two memo files that were used to create the 2skyCometDB and 2skyAsteroidDB:
2sky Asteroids
2453000.5 317.77388 2.7659574 0.0795184 74.06844 80.47940 10.58343 3.34 0.12 (1) Ceres
2453000.5 15.64391 2.3614312 0.0886425 150.22064 103.93760 7.13329 3.2 0.32 (4) Vesta
2453000.5 65.96111 2.4252894 0.2012031 238.94454 138.84621 14.76742 5.71 0.24 (6) Hebe
2453000.5 240.05292 2.3472321 0.1715905 356.52379 94.81449 1.58365 7.0 0.15 (27) Euterpe
2452600.5 218.05718 2.27733478 0.2299714 310.42308 173.16621 34.84637 4.13 0.11 (2) Pallas
2453200.5 334.07658 2.511599 0.6336092 274.80442 128.19927 0.46975 15.30 0.10 (4179) Toutatis
2sky Comets
2453160.5 2453141.464 0.961957 1.000664 1.2038 210.2786 99.6426 5.0 7.5 C/2001 Q4 (NEAT)
2453120.5 2453118.56 0.614599 1.000561 157.7359 94.8589 160.5833 5.5 7.5 C/2002 T7 (LINEAR)
2453395.349 2453395.349 1.20379 0.9999999 19.571 93.589 38.595 5.5 10.0 C/2004 Q2 (Machholz)
2453280.5 2453292.215 1.023621 1.000360 198.4401 18.6752 134.2527 4.0 8.0 C/2003 K4 (LINEAR)
2453480.5 2453464.1259 0.849656 1.000617 181.6760 93.9042 86.7620 6.5 8.0 C/2003 T4 (LINEAR)