Use local apparent instead of local mean sidereal time for hour angle#225
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rhannequin merged 1 commit intomainfrom Oct 21, 2025
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Use local apparent instead of local mean sidereal time for hour angle#225rhannequin merged 1 commit intomainfrom
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To improve accuracy of horizontal coordinates from equatorial ones, the hour angle should be computed using local apparent sidereal time instead of local mean sidereal time. This only change enables to reach an average difference with Skyfield for horizontal coordinates of planets of ~0.35 arcseconds. This angular distance represents the separation of some tight double stars, barely resolvable y large amateur telescopes under good seeing.
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## 0.9.0 - 2025-10-31 _If you are upgrading: please see [UPGRADING.md]._ ### Features * Add `#approaching_primary?` and `#receding_from_primary?` to solar system bodies ([#211]) * Calculate apoapsis and periapsis events ([#213]) * Improve precision of ΔT ([#219]) * Deep Sky Object: Compute astrometric position ([#217]) * Deep Sky Object: Compute apparent position ([#220]) * Deep Sky Object: Handle velocities properly ([#222]) * Deep Sky Object: Compute topocentric position ([#226]) * Deep Sky Object: difference between the body and the position ([#227]) * Deep Sky Object: Add support for RiseTransitSetCalculator ([#228]) ### Improvements * Drop `Astronoby::Apparent#angular_diameter` ([#221]) * Bump rubyzip from 3.0.2 to 3.2.1 by @dependabot ([#210], [#215], [#223], [#233]) * Bump standard from 1.50.0 to 1.51.1 by @dependabot ([#212], [#214]) * Be proud about the precision achieved ([#218]) * Use local apparent instead of local mean sidereal time for hour angle ([#225]) * Bump rspec from 3.13.1 to 3.13.2 by @dependabot ([#229]) * Bump benchmark from 0.4.1 to 0.5.0 by @dependabot ([#230]) * Add documentation for deep-sky objects ([#232]) * Bump rake from 13.3.0 to 13.3.1 by @dependabot ([#235]) ### Backward-incompatible changes * Drop `Astronoby::Apparent#angular_diameter` ([#221]) * Use local apparent instead of local mean sidereal time for hour angle ([#225]) **Full Changelog**: v0.8.0...v0.9.0 [#210]: #210 [#211]: #211 [#212]: #212 [#213]: #213 [#214]: #214 [#215]: #215 [#217]: #217 [#218]: #218 [#219]: #219 [#220]: #220 [#221]: #221 [#222]: #222 [#223]: #223 [#225]: #225 [#226]: #226 [#227]: #227 [#228]: #228 [#229]: #229 [#230]: #230 [#232]: #232 [#233]: #233 [#235]: #235 [UPGRADING.md]: https://github.com/rhannequin/astronoby/blob/main/UPGRADING.md
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To improve accuracy of horizontal coordinates from equatorial ones, the hour angle should be computed using local apparent sidereal time instead of local mean sidereal time.
This only change enables to reach an average difference with Skyfield for horizontal coordinates of planets of ~0.35 arcseconds. This angular distance represents the separation of some tight double stars, barely resolvable y large amateur telescopes under good seeing.