skymath 0.3.4

Planning-grade astronomy math for astrophotography tooling: angles, equatorial coordinates, sexagesimal parsing and formatting, angular separation and offsets, precession, MJD/JD/calendar conversions, sidereal time, and observer-local quantities (alt-az, airmass, transit).
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135

#!/usr/bin/env python3
"""Generate src/constellation_data.rs from the Roman (1987) boundary table.

Data source: ADC/CDS catalogue VI/42 (Roman 1987, PASP 99, 695) — fetched from
CDS when reachable, otherwise the byte-identical copy bundled with AstroPy
(astropy/coordinates/data/constellation_data_roman87.dat). The 88 official
names come from AstroPy's constellation_names.dat (IAU list via VizieR).

Run from the repo root (same environment as gen_astropy_vectors.py):

    uv run --with astropy scripts/gen_constellation_table.py

The generated file is committed; rerunning must be byte-stable for a given
catalogue revision. Records keep catalogue order and the original decimal
literals (first matching record wins in the Roman walk; see research R19/R22).
"""

from pathlib import Path
from urllib.request import urlopen

CDS_URL = "https://cdsarc.cds.unistra.fr/ftp/VI/42/data.dat"
OUT = Path("src/constellation_data.rs")


# AstroPy's constellation_names.dat carries three misspellings; skymath ships
# the official IAU forms (the AstroPy vectors compare abbreviations, and the
# full-name check special-cases these — see tests/astropy_vectors.rs).
IAU_SPELLING = {
    "Chamaleon": "Chamaeleon",
    "Ophiucus": "Ophiuchus",
    "Pisces Austrinus": "Piscis Austrinus",
}


def names_table():
    """[(abbr, full_name)] in IAU list order (alphabetical by full name)."""
    import astropy.coordinates as ac

    path = Path(str(ac.__file__)).parent / "data" / "constellation_names.dat"
    rows = []
    for line in path.read_text(encoding="utf-8").splitlines():
        line = line.strip()
        if not line or line.startswith("#"):
            continue
        abbr, full = line.split(maxsplit=1)
        rows.append((abbr, IAU_SPELLING.get(full, full)))
    if len(rows) != 88:
        raise SystemExit(f"expected 88 constellation names, got {len(rows)}")
    return rows


def zone_lines():
    """Raw data lines of VI/42: CDS first, AstroPy bundled copy as fallback."""
    try:
        text = urlopen(CDS_URL, timeout=10).read().decode("ascii")
        source = CDS_URL
    except Exception as exc:  # noqa: BLE001 — any failure means use fallback
        import astropy.coordinates as ac

        path = Path(str(ac.__file__)).parent / "data" / "constellation_data_roman87.dat"
        text = path.read_text(encoding="ascii")
        source = f"astropy bundled copy ({exc.__class__.__name__} from CDS)"
    lines = [
        ln for ln in text.splitlines() if ln.strip() and not ln.lstrip().startswith("#")
    ]
    if len(lines) != 357:
        raise SystemExit(f"expected 357 zone records, got {len(lines)} ({source})")
    print(f"source: {source}")
    return lines


def main():
    names = names_table()
    by_lower = {abbr.lower(): abbr for abbr, _ in names}

    records = []
    for ln in zone_lines():
        ra_lo, ra_hi, dec_lo, code = ln.split()
        # Serpens is split into two catalogue regions (Ser1/Ser2) — one variant.
        key = code.rstrip("0123456789").lower()
        if key not in by_lower:
            raise SystemExit(f"unknown constellation code {code!r}")
        for tok, span in ((ra_lo, (0.0, 24.0)), (ra_hi, (0.0, 24.0)), (dec_lo, (-90.0, 90.0))):
            v = float(tok)
            if not span[0] <= v <= span[1]:
                raise SystemExit(f"value {tok} out of range in record {ln!r}")
        records.append((ra_lo, ra_hi, dec_lo, by_lower[key]))

    last = records[-1]
    if (float(last[0]), float(last[1]), float(last[2]), last[3]) != (0.0, 24.0, -90.0, "Oct"):
        raise SystemExit(f"unexpected final (south-cap) record: {last}")

    body = "\n".join(
        f"    ({float(lo)}, {float(hi)}, {float(dl)}, C::{abbr})," for lo, hi, dl, abbr in records
    )
    OUT.write_text(
        f'''//! Roman (1987) precomputed constellation boundary zones — GENERATED FILE.
//!
//! Generated by `scripts/gen_constellation_table.py`; DO NOT EDIT by hand.
//! Source: ADC/CDS catalogue VI/42 (Roman 1987, PASP 99, 695), the IAU
//! (Delporte 1930) constellation boundaries precomputed as declination-zone
//! records at epoch B1875.0. Record order is the catalogue's: the first
//! matching record wins in the lookup walk (see `crate::constellation`).

use crate::constellation::Constellation as C;

/// `(ra_lo, ra_hi, dec_lo, constellation)` — RA in B1875 hours, Dec in B1875
/// degrees; a record matches when `dec >= dec_lo && ra_lo <= ra < ra_hi`.
pub(crate) const ZONES: [(f64, f64, f64, C); 357] = [
{body}
];
''',
        encoding="utf-8",
    )
    print(f"wrote {OUT} ({len(records)} records)")

    # Companion blocks for src/constellation.rs (pasted once, kept in sync by
    # the AstroPy full-name vectors): variants, ALL, abbreviations, names.
    scratch = Path("target/constellation_enum_blocks.rs")
    scratch.parent.mkdir(exist_ok=True)
    variants = "\n".join(
        f"    /// {full} ({abbr}).\n    {abbr}," for abbr, full in names
    )
    all_arr = "\n".join(f"        Constellation::{abbr}," for abbr, _ in names)
    abbrs = "\n".join(f'    "{abbr}",' for abbr, _ in names)
    fulls = "\n".join(f'    "{full}",' for _, full in names)
    scratch.write_text(
        f"// variants\n{variants}\n// ALL\n{all_arr}\n// ABBR\n{abbrs}\n// NAMES\n{fulls}\n",
        encoding="utf-8",
    )
    print(f"wrote {scratch}")


if __name__ == "__main__":
    main()