View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0002809 | SkyChart | 1-Software | public | 25-03-11 08:07 | 25-03-15 14:20 |
| Reporter | Mattia Verga | Assigned To | |||
| Priority | normal | Severity | feature | Reproducibility | N/A |
| Status | new | Resolution | open | ||
| Summary | 0002809: Solar longitude in planets info | ||||
| Description | Is it possible to add the solar longitude Ls in the info tab about planets? https://en.wikipedia.org/wiki/Solar_longitude This is especially useful in Mars observations: https://www-mars.lmd.jussieu.fr/mars/time/solar_longitude.html Or maybe is already there somewhere and I can't find it?... | ||||
| Tags | No tags attached. | ||||
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No, this is not computed. The solar latitude is given in field "Sun inclination", I need to look if I can find a way to compute the longitude. The page you indicate https://www-mars.lmd.jussieu.fr/mars/time/martian_time.html include a link to a calculator. I look at the script, this is very low precision but maybe enough for the use? There is probably no use for the other planets that not have "seasons". |
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Yeah, I think low precision is enough. However, the term "solar longitude" is a bit tricky, as I discovered myself. As I understand, the field "sun inclination" is about the sub-solar latitude of the Sun on the target. There is also a sub-solar longitude of the Sun on the target, which is different than the Ls "solar longitude". NASA Horizon System manual (https://ssd.jpl.nasa.gov/horizons/manual.html) descriptions are under: 15. Solar sub-longitude & sub-latitude 44. Apparent target-centered longitude of the Sun (apparent L_s) As of now, I've been unable to locate the formula used by Horizon to calculate those. |
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Yes the definition can be confusing. In this case this is the longitude of the Sun measured from the martian spring equinox position. This is not directly related to the sub-solar latitude, but at the martian equinox the sub-solar latitude is zero. The sub-solar longitude is related to the planet rotation, instead of this the program display the central meridian longitude (sub-earth longitude) that is more meaningful for observer. All the method I find count the number of rotation from a reference epoch where solar longitude was zero, then compute the difference of longitude since the last spring. |
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I find a good method, not too complicated to implement and relatively precise. This is in this paper: https://www.lpl.arizona.edu/~shane/publications/piqueux_etal_icarus_2015.pdf I take the simplified method without all the planetary perturbations for a display to 0.1°. For today 18h UT this give 56.2 where Horizon give 56.1983646 The code change: https://github.com/pchev/skychart/commit/6e974411bb410d58451f268e4ed16c84d050db43 This will be in the daily version tomorrow: https://vega.ap-i.net/pub/skychart/daily_build/ |
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Thanks, will try soon! |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 25-03-11 08:07 | Mattia Verga | New Issue | |
| 25-03-11 21:27 | Patrick Chevalley | Note Added: 0009325 | |
| 25-03-12 10:36 | Mattia Verga | Note Added: 0009326 | |
| 25-03-12 12:51 | Patrick Chevalley | Note Added: 0009327 | |
| 25-03-13 22:09 | Patrick Chevalley | Note Added: 0009328 | |
| 25-03-15 14:20 | Mattia Verga | Note Added: 0009343 |
