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Big Sky Star Catalog

The Big Sky Star Catalog contains 2,557,500 stars compiled from the following catalogs: Hipparcos, Tycho-1, and Tycho-2. The position of each star is normalized to the J2000 Epoch, using the wonderful Python library Skyfield.

For complete details of how the Big Sky Star Catalog is created, check out bigsky/builders/stars.py.

Column Descriptions

tyc_id

  • String

  • Tycho ID, formatted as a string with hyphens (e.g. 6-1005-1)

hip_id

  • Integer

  • Hipparcos ID

ccdm

  • String

  • CCDM Component Identifier (if applicable)

magnitude

  • Float

  • Visual apparent magnitude (Johnson V)

  • Rounded to two decimal places

  • The Johnson V value is not in the Tycho-2 catalog directly, so the value in Big Sky is taken from Tycho-1 if available. For stars that are in Tycho-2 but not Tycho-1, then the following formula is used to convert Tycho-2's BT/VT magnitudes to Johnson V:

    V = VT - 0.090 * (BT-VT)

    * Formula obtained from the Tycho-2 Readme

    * if BT or VT magnitude is not available for the star in Tycho-2, then the magnitude in Big Sky is listed as VT if that's available, otherwise it's listed as BT (one of these is always available in Tycho-2)

bv

  • Float

  • BV Color Index

  • Rounded to two decimal places

  • This is a calculated value from each star's VT/BT magnitudes, using the following formula:

    B-V = 0.850 * (BT-VT)

    * Formula obtained from the Tycho-2 Readme

    * If the star does not have a BT or VT value, then the B-V is listed as null in Big Sky

ra_degrees_j2000

  • Float

  • Right Ascension in degrees (0 to 360) and Epoch J2000.0

  • Rounded to four decimal places

  • For stars from Tycho-2, this is the observed RA converted to the J2000 Epoch

  • For stars from Hipparcos/Tycho-1, this is the listed RA from Tycho-2's supplement file, and converted to the J2000 Epoch

dec_degrees_j2000

  • Float

  • Declination in degrees (-90 to 90) and Epoch J2000.0

  • Rounded to four decimal places

  • For stars from Tycho-2, this is the observed DEC converted to the J2000 Epoch

  • For stars from Hipparcos/Tycho-1, this is the listed DEC from Tycho-2's supplement file, and converted to the J2000 Epoch

ra_mas_per_year

  • Float

  • Rounded to two decimal places

  • This value is from Tycho-2 if available for the star, otherwise it's taken from Tycho-1 if available there. If it's not listed in either catalog, then it will be listed as 0 in Big Sky.

dec_mas_per_year

  • Float

  • Rounded to two decimal places

  • This value is from Tycho-2 if available for the star, otherwise it's taken from Tycho-1 if available there. If it's not listed in either catalog, then it will be listed as 0 in Big Sky.

parallax_mas

  • Float

  • Rounded to two decimal places

  • This value is not available for any star in Tycho-2, so it's taken from Tycho-1 if available

name

  • String
  • Name of the star, as designated by IAU
  • Exception: the name listed for HIP 39953 is "Regor", in honor of astronauts :)

hd_id

  • Integer
  • Henry Draper catalog number, if available

bayer

  • String
  • Bayer designation, if available
  • Only Greek letter designations are listed

flamsteed

  • Integer
  • Flamsteed number, if available

constellation

  • String
  • Constellation the star belongs to, as 3-letter IAU abbreviation

References

Spot an error?

If you see an error in any of this documentation or in the data itself, please open a GitHub issue about it. Your help is greatly appreciated!