View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0001548 | SkyChart | 3-Documentation | public | 16-08-14 16:03 | 17-01-15 17:50 |
| Reporter | jsrt | Assigned To | |||
| Priority | normal | Severity | feature | Reproducibility | N/A |
| Status | resolved | Resolution | fixed | ||
| Target Version | 4.0 | Fixed in Version | 3.11 SVN | ||
| Summary | 0001548: What is the distinction between Mean J2000 and Astrometric J2000 in the Coordinates settings ? | ||||
| Description | IIUC, if one of these two options is selected in the Configuration settings, then objects (and grids) will be displayed with their J2000 coordinates (independently of the actual date). But what is the difference btw these two options ? Also what is the meaning of the second option ("Mean of the date") ? Sorry if this is not specific to SkyChart but I could not find an answer in astrometry textbooks. | ||||
| Tags | No tags attached. | ||||
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You are probably not the only one to have problem with this setting, so I added some information in the documentation for the next release. See https://www.ap-i.net/skychart/en/documentation/chart_coordinates#type_of_coordinates For a direct answer, the difference between Mean J2000 and Astrometric J2000 is the first one use the proper motion for 2000.0, but the second the proper motion for the epoch of the chart. This is used for astrometry measurement when people want J2000 coordinates but also want to correct the reference star position for the date of the observation. "Mean of the date" use the mean equinox of the date, without nutation and aberration correction. Many printed almanac use this system. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 16-08-14 16:03 | jsrt | New Issue | |
| 16-08-14 19:18 | Patrick Chevalley | Project | CCdciel => SkyChart |
| 16-08-14 19:18 | Patrick Chevalley | Category | (No Category) => General |
| 16-08-14 19:30 | Patrick Chevalley | Note Added: 0003374 | |
| 16-08-14 19:30 | Patrick Chevalley | Status | new => resolved |
| 16-08-14 19:30 | Patrick Chevalley | Resolution | open => fixed |
| 16-08-14 19:30 | Patrick Chevalley | Category | General => 3-Documentation |
| 16-08-14 19:30 | Patrick Chevalley | Product Version | 0.3.0 => |
| 16-08-14 19:30 | Patrick Chevalley | Fixed in Version | => 4.0 |
| 16-08-14 19:30 | Patrick Chevalley | Target Version | => 4.0 |
| 17-01-15 17:50 | Patrick Chevalley | Fixed in Version | 4.0 => 3.11 SVN |
