Merged
Conversation
Delta T (ΔT) is a measure of the difference between the fixed-length day of International Atomic Time (TAI, always 86400 seconds) and Universal Time based on Earth's rotation (which can slightly vary and create this difference). The measurement started in the early 1900, its value needs to be taken into account when converting civil time to terrestrial time, which is used in most astronomical algorithms. Astronoby uses a fixed list of values of ΔT for specific TT dates. In calculations, the most appropriate value of ΔT is fetched. To increase precision, intermediate values have been added, and values themselves have been improved in precision by 3 digits. This explains why some many tests have been updated in this change, to reflect the new expectations of Astronoby. Almost all updated tests show improvement of accuracy compared to sources of truth. The only few cases where accuracy seems to have slightly reduces are due to external precision issues.
Merged
rhannequin
added a commit
that referenced
this pull request
Oct 31, 2025
## 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
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Delta T (ΔT) is a measure of the difference between the fixed-length day of International Atomic Time (TAI, always 86400 seconds) and Universal Time based on Earth's rotation (which can slightly vary and create this difference).
The measurement started in the early 1900, its value needs to be taken into account when converting civil time to terrestrial time, which is used in most astronomical algorithms.
Astronoby uses a fixed list of values of ΔT for specific TT dates. In calculations, the most appropriate value of ΔT is fetched.
To increase precision, intermediate values have been added, and values themselves have been improved in precision by 3 digits.
This explains why some many tests have been updated in this change, to reflect the new expectations of Astronoby. Almost all updated tests show improvement of accuracy compared to sources of truth. The only few cases where accuracy seems to have slightly reduces are due to external precision issues.