# Deep-sky catalogue (`data/deep_sky.csv`) — sources and licence

`data/deep_sky.csv` lists 204 nebulae, star clusters and galaxies for the holo
map. It is generated by `tools/build_deep_sky.py` (run it to reproduce the file
exactly) and is an **adapted database of OpenNGC**, so it is distributed under
the same licence:

**Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)**
— https://creativecommons.org/licenses/by-sa/4.0/

## Positions, types, sizes, magnitudes, names

* **OpenNGC** by Mattia Verga — https://github.com/mattiaverga/OpenNGC
  (release `v20231203`, files `database_files/NGC.csv` and `addendum.csv`),
  CC BY-SA 4.0. Used for RA/Dec (J2000), object type, major/minor axis
  (arcmin), position angle, V (or B) magnitude, constellation, Messier
  cross-reference and common names.
* Changes made: selection of objects (all Messier objects except M40, M73 and
  the M102 duplicate, plus a curated set of NGC/IC/Melotte/Caldwell objects),
  type mapping to game categories, display names, added distances.
* **Galaxy sizes** (major axis D25 and minor axis D25 / R25) come from
  **HyperLEDA** as published by Paturel G. et al. 2003, A&A 412, 45 (VizieR
  VII/237), one cone query per galaxy, taking the largest D25 in the cone.
  OpenNGC's axes were off by up to a factor of two for some galaxies (M108
  3.98′ against D25 7.76′). The three dwarf spheroidals (Sculptor, Fornax,
  Leo I) keep OpenNGC's axes: they have no 25 mag/arcsec² isophote.
  Acknowledgement: "We acknowledge the usage of the HyperLEDA database
  (http://leda.univ-lyon1.fr)" (Makarov D. et al. 2014, A&A 570, A13).
* Objects not in OpenNGC (Galactic Centre, Alpha Persei Cluster, NGC 2451A and
  nine nearby molecular clouds) have positions/extents typed in by hand from
  the references below; cloud extents are approximate outlines, not survey
  boundaries.
* The 22 unnamed open clusters in tier 2 (Platais, UPK, Alessi, ASCC, UBC …)
  take position and size (2 × r50) from Cantat-Gaudin et al. 2020.

## Distances

Distances are per row in `dist_ly` (light-years, 1 pc = 3.26156 ly) with the
source key in `dist_src`:

| key | reference | used for |
|-----|-----------|----------|
| CG2020 | Cantat-Gaudin T. et al. 2020, A&A 640, A1 — Gaia DR2 open clusters (VizieR J/A+A/640/A1). d = 1000/(ϖ + 0.029 mas) pc; the catalogue's DistPc when ϖ < 0.2 mas | open clusters; Eagle (NGC 6611), Carina (Trumpler 16), Rosette (NGC 2244), Heart (IC 1805), Soul (IC 1848), M24 (its embedded cluster NGC 6603) |
| BV2021 | Baumgardt H. & Vasiliev E. 2021, MNRAS 505, 5957 (distances as tabulated in H. Baumgardt's Galactic globular cluster database) | globular clusters |
| CW2021 | Chornay N. & Walton N. A. 2021, A&A 656, A110 — Gaia EDR3 PN central stars (VizieR J/A+A/656/A110), column rcomb | planetary nebulae |
| Menten2007 | Menten K. M. et al. 2007, A&A 474, 515 (414 pc) | M42, M43 |
| Kounkel2017 | Kounkel M. et al. 2017, ApJ 834, 142 (VLBA: NGC 2068 388 pc, NGC 2024 ~420 pc) | M78, Flame, Horsehead |
| Kuhn2019 | Kuhn M. A. et al. 2019, ApJ 870, 32 (VizieR J/ApJ/870/32, Gaia DR2 members) | Lagoon (M8, 1336 pc), Trifid (M20, 1264 pc) |
| Kuhn2020 | Kuhn M. A. et al. 2020, ApJ 899, 128 | North America Nebula |
| Xu2011 | Xu Y. et al. 2011, ApJ 733, 25 | Omega Nebula (M17) |
| Fesen2021 | Fesen R. A. et al. 2021, MNRAS 507, 244 (Cygnus Loop, 725 ± 15 pc, Gaia EDR3; supersedes Fesen et al. 2018's 735 pc) | Veil Nebula |
| Lada2009 | Lada C. J. et al. 2009, ApJ 703, 52 | California Nebula |
| Trimble1973 | Trimble V. 1973, PASP 85, 579 (~2 kpc) | Crab Nebula |
| GRAVITY2019 | GRAVITY Collaboration 2019, A&A 625, L10 (R0 = 8.178 kpc) | Galactic Centre |
| Pietrzynski2019 | Pietrzyński G. et al. 2019, Nature 567, 200 | LMC, Tarantula |
| Graczyk2020 | Graczyk D. et al. 2020, ApJ 904, 13 | SMC |
| McConnachie2012 | McConnachie A. W. 2012, AJ 144, 4 | Local Group galaxies |
| Mei2007 | Mei S. et al. 2007, ApJ 655, 144 (Virgo Cluster mean, 16.5 Mpc) | Virgo Cluster Messier galaxies |
| Freedman1994 | Freedman W. L. et al. 1994, ApJ 427, 628 | M81 |
| Freedman2001 | Freedman W. L. et al. 2001, ApJ 553, 47 | M95, M96, NGC 7331 |
| Dalcanton2009 | Dalcanton J. J. et al. 2009, ApJS 183, 67 | M82, NGC 55, NGC 300, NGC 2403 |
| Shappee2011 | Shappee B. J. & Stanek K. Z. 2011, ApJ 733, 124 | M101 |
| McQuinn2016a | McQuinn K. B. W. et al. 2016, ApJ 826, 21 (TRGB, 8.58 Mpc) | M51 |
| McQuinn2016b | McQuinn K. B. W. et al. 2016, AJ 152, 144 (TRGB, 9.55 Mpc) | M104 |
| McQuinn2017 | McQuinn K. B. W. et al. 2017, AJ 154, 51 (TRGB: M63 8.87, M74 9.77 Mpc) | M63, M74 |
| Humphreys2013 | Humphreys E. M. L. et al. 2013, ApJ 775, 13 | M106 |
| Tonry2001 | Tonry J. L. et al. 2001, ApJ 546, 681 (SBF, NGC 3379 (m−M) = 30.12) | M105 |
| Harris2010 | Harris G. L. H. et al. 2010, PASA 27, 457 | Centaurus A |
| RadburnSmith2011 | Radburn-Smith D. J. et al. 2011, ApJS 195, 18 | NGC 253, NGC 4565, NGC 4631 |
| Tully2013 | Tully R. B. et al. 2013, AJ 146, 86 (Cosmicflows-2, VizieR J/AJ/146/86) | M83 |
| Tully2023 | Tully R. B. et al. 2023, ApJ 944, 94 (Cosmicflows-4, VizieR J/ApJ/944/94; galaxy DM, or the group mean where the galaxy's own value is Tully–Fisher only) | M64, M65, M66, M94, M108, M109 |
| Tully1988 | Tully R. B. 1988, *Nearby Galaxies Catalog* (VizieR VII/145; H0 = 75 flow-model distance) | M77 |
| Galli2019/2020/2021 | Galli P. A. B. et al. 2019 A&A 630, A137 (Taurus); 2020 A&A 643, A148 (Lupus, ~160 pc) and A&A 634, A98 (Corona Australis, 149.4 pc); 2021 A&A 646, A46 (Cha I, 186.7–191.4 pc) | Taurus, Lupus, Corona Australis, Chamaeleon I clouds |
| OrtizLeon2017a | Ortiz-León G. N. et al. 2017, ApJ 834, 141 (VLBA, L1688 137.3 pc) | ρ Ophiuchi cloud |
| OrtizLeon2017b | Ortiz-León G. N. et al. 2017, ApJ 834, 143 (VLBA, Serpens/W40 436.0 pc) | Serpens cloud |
| OrtizLeon2018 | Ortiz-León G. N. et al. 2018, ApJ 865, 73 (IC 348 321 pc, NGC 1333 293 pc) | Perseus cloud |
| Zucker2020 | Zucker C. et al. 2020, A&A 633, A51 (Gaia DR2 + dust; Coalsack 189 pc, as listed in SIMBAD) | Coalsack |
| Alves2007 | Alves F. O. & Franco G. A. P. 2007, A&A 470, 597 | Pipe Nebula |

Literature distances are rounded to the precision a star map needs; molecular
clouds are extended (tens of parsecs deep) and carry one representative
distance. Distances (facts) are not themselves copyrightable; the citations
are given so every number can be checked.

## Verification of the literature distances (2026-09)

The `LIT` table in `tools/build_deep_sky.py` had been typed from memory. Every
entry (66 objects plus the Virgo mean used for 16 cluster members) was checked
against a source reachable from the build machine: the paper's abstract or full
text on arXiv, its VizieR table, SIMBAD's distance measurements (`mesDistance`),
and the Cosmicflows-2/-4 compilations (VizieR J/AJ/146/86, J/ApJ/944/94) as a
cross-check for every galaxy. 41 were confirmed as typed. The rows below changed
(19 values, 6 citation-only fixes; distances in the source's unit):

| object | was | now | source checked |
|--------|-----|-----|----------------|
| M20 Trifid | 1.2 kpc, approx | 1.264 kpc, Kuhn2019 | VizieR J/ApJ/870/32 table1 (M20: 1264 pc) |
| M24 Sgr Star Cloud | 3.0 kpc, approx | 2.83 kpc, CG2020 (NGC 6603) | VizieR J/A+A/640/A1 (NGC 6603 ϖ = 0.324 mas) |
| Coalsack | 185 pc, approx | 189 pc, Zucker2020 | SIMBAD mesDistance (2020A&A...633A..51Z) |
| M78 | 400 pc | 388 pc | Kounkel2017 abstract (NGC 2068: 388 ± 10 pc) |
| NGC 2024 Flame | 400 pc | 420 pc | Kounkel2017 abstract ("roughly ~420 pc") |
| Veil (NGC 6960/6992) | 735 pc, Fesen2018 | 725 pc, Fesen2021 | arXiv:2109.05368 (EDR3 update by the same authors) |
| Lupus clouds | 158 pc | 160 pc | Galli2020 abstract ("about 160 pc") |
| ρ Oph cloud | OrtizLeon2018a | OrtizLeon2017a (137 pc unchanged) | 137.3 pc is ApJ 834, 141; ApJ 869, L33 gives 138–144 pc |
| Serpens / Perseus | OrtizLeon2017 / 2018b | OrtizLeon2017b / 2018 (values unchanged) | keys made unambiguous |
| NGC 55 | 2.0 Mpc | 2.1 Mpc | Dalcanton2009 TRGB table (2.08–2.12 Mpc) |
| M63 | 9.04 Mpc | 8.87 Mpc | McQuinn2017 table (9.04 was the Cosmicflows-2 value) |
| M74 | 9.8 Mpc, Tully2013 | 9.77 Mpc, McQuinn2017 | M74 is not in Cosmicflows-2; McQuinn2017 TRGB |
| M51 / M104 | McQuinn2016 (AJ 152, 144) | McQuinn2016a (ApJ 826, 21) / 2016b | two separate papers; values unchanged |
| M94 | 4.66 Mpc, Tully2013 | 4.34 Mpc, Tully2023 | CF2 has 4.59 (4.66 is M83's); CF4 TRGB-based 4.34 |
| M64 | 5.3 Mpc, Tully2013 | 4.36 Mpc, Tully2023 | CF4 (TRGB 28.17 mag) |
| M65 | 10.6 Mpc, Tully2013 | 11.4 Mpc, Tully2023 | CF2 12.19 (TF); CF4 Leo Triplet group 11.4 |
| M66 | 10.6 Mpc, Tully2013 | 10.3 Mpc, Tully2023 | CF2 9.04; CF4 10.31 (TRGB + Cepheid) |
| M108 | 8.8 Mpc, Tully2013 | 9.2 Mpc, Tully2023 | CF2 10.0, CF4 9.18 (both TF) |
| M109 | 18.4 Mpc, Tully2013 | 20.9 Mpc, Tully2023 | CF2 26.8 / CF4 25.2 are single TF values; CF4 group mean 20.9 |
| M77 | 14.4 Mpc, Tully2013 | 14.4 Mpc, Tully1988 | not in CF2/CF4; 14.4 is the NBG value (VizieR VII/145) |
| M96 | 10.7 Mpc | 10.52 Mpc | Freedman2001 Table 3 (NGC 3368, Z-corrected) |
| M105 | 10.3 Mpc | 10.57 Mpc | Tonry2001 table (NGC 3379, (m−M) = 30.12) |

Confirmed as typed (source in brackets): M1 (SIMBAD, Trimble 1973), M8 and
M17 (Kuhn2019 table / Xu2011 abstract 1.98 kpc), M42/M43 (Menten2007 abstract
414 pc), B 33, NGC 7000 (Kuhn2020 full text 795 pc), NGC 1499 (Lada2009
abstract 450 pc), NGC 2070/LMC (Pietrzyński2019 49.59 kpc), SMC (Graczyk2020
62.44 kpc), Sgr A* (GRAVITY2019 8178 pc), all 12 McConnachie2012 Local Group
rows (VizieR J/AJ/144/4), M81 and M95/NGC 7331 (Freedman2001 Table 3: 3.63,
10.00, 14.72 Mpc), M82/NGC 300/NGC 2403 (Dalcanton2009 TRGB table), M101
(Shappee2011 abstract 6.4 Mpc), M51/M104 (McQuinn2016a/b abstracts), M106
(Humphreys2013 abstract 7.60 Mpc), M83 (CF2 4.66 Mpc), NGC 5128 (Harris2010
abstract 3.8 Mpc), Virgo mean (Mei2007 abstract 16.5 Mpc), Taurus, Corona
Australis, Chamaeleon I (Galli abstracts), Serpens and Perseus (Ortiz-León
abstracts). Not reachable, kept: NGC 253 / NGC 4565 / NGC 4631
(Radburn-Smith2011 is not on arXiv or VizieR; the values agree with CF2/CF4 to
within 3%) and the Pipe Nebula (Alves & Franco 2007, 145 pc; Gaia-era
estimates for B59 are 163–180 pc).