Skip to content

Yale BSC5 Format

Jump to bottom
William Forney edited this page Mar 10, 2026 · 1 revision

Yale Bright Star Catalog, 5th Edition (BSC5) Format

This document describes the fixed-width ASCII record format of the Yale Bright Star Catalog (BSC5), 5th revised edition. The catalog data is not included in this repository; it must be obtained separately from an astronomical data archive.

Overview

The Yale BSC5 contains 9,096 stars with visual magnitudes brighter than approximately 7.1. Every star record is a single line of exactly 197 characters (plus line ending). Fields are positional — column numbers below are 0-based and the end column is exclusive (Python/C# slice convention: line[start..end]).

All coordinates are J2000.0 mean equatorial (ICRS-compatible for the vast majority of bright stars).

Field Definitions

Field Cols (0-based) Width Type Units / Notes
HR number 0–3 4 int Harvard Revised (HR) catalog number. Right-justified. Blank = not applicable (skip record).
Star name 4–13 10 string Name as given in the catalog; trimmed. May be blank.
RA hours (J2000) 75–76 2 int Hours component of right ascension.
RA minutes 77–78 2 int Minutes component of right ascension.
RA seconds 79–82 4 float Decimal seconds component of right ascension (e.g. 23.46).
Dec sign 83 1 char + or -.
Dec degrees 84–85 2 int Degrees component of declination (absolute value).
Dec arcminutes 86–87 2 int Arcminutes component of declination.
Dec arcseconds 88–89 2 int Integer arcseconds component of declination.
Visual magnitude 102–106 5 float V-band apparent magnitude. May include sign (e.g. -1.46, 0.03).
Spectral type 127–146 20 string MK spectral classification (trimmed). May be blank.
PM RA (s/yr) 148–153 6 float Annual proper motion in RA, in seconds of time per year. This is the rate of change of the RA coordinate itself (already includes cos δ factor implicitly at the catalog epoch).
PM Dec (arcsec/yr) 154–159 6 float Annual proper motion in declination, in arcseconds per year.
Parallax (arcsec) 161–165 5 float Trigonometric parallax in arcseconds. Multiply by 1000 for mas.

Unit Conversions Used by YaleBsc5Reader

BSC5 field BSC5 unit FixedStar field FixedStar unit Conversion
PM RA s of time / yr ProperMotionRaCosD mas / yr value × 15.0 × 1000.0 × cos(δ)
PM Dec arcsec / yr ProperMotionDec mas / yr value × 1000.0
Parallax arcsec ParallaxMas mas value × 1000.0

Note on PM RA convention: The BSC5 records proper motion in RA as the change in the RA coordinate itself (in time units). To convert to the μα cos δ convention used by FixedStar (linear motion on the sky), multiply by cos(δ). The factor of 15 converts seconds of time to arcseconds; multiplying by 1000 gives mas/yr.

Obtaining the Catalog

The BSC5 catalog file (typically named catalog with no extension) is available at:

Download the file, verify it contains ~9,096 lines of 197 characters each, then pass its absolute path to YaleBsc5Reader.Load(filePath).

Example Record

   1Alp And          ....  006 44 47.0  23 12 06  ...  2.07  A0pSiSrCrEu  .........
^  ^                                                   ^     ^
|  |                                                   |     Spectral type (cols 127–146)
|  Star name (cols 4–13)                               Visual magnitude (cols 102–106)
HR number (cols 0–3)

(Field positions above are illustrative; real records do not contain spaces as shown.)

Related Source Files

  • Ephemeris/Stellarography/YaleBsc5Reader.cs — implementation
  • Ephemeris/Stellarography/FixedStar.cs — output record type
  • docs/sefstars-format.md — format documentation for the SE1 / sefstars.txt catalog

Clone this wiki locally