Summary of the Hipparcos and Tycho Catalogues

 Measurement period  1989.85 - 1993.21
 Catalogue epoch  J1991.25
 Reference system  ICRS
 Coincidence with respect to ICRS (all 3 axes)  Formula: 0 0.6 mas
 Proper motion deviation from inertial (all 3 axes)   Formula: 1 0.25  mas/yr

Hipparcos Catalogue:

Number of entries 118218
Entries with associated astrometry 117955
Entries with associated photometry 118204
Mean sky density  ~ 3 per square degree
Limiting magnitude  V ~ 12.4 mag
Completeness  Up to V = 7.3 - 9.0 mag
   
Median precision of positions, J1991.25 (Hp < 9 mag)  0.77/0.64 mas (RA/dec)
Median Precision of parallaxes (Hp < 9 mag)  0.97 mas
Median precision of proper motion (Hp < 9 mag)  0.88/0.74 mas/yr (RA/dec)
10 per cent (each of the five parameters) better than  0.47-0.66 mas
Distance determined to better than 10 per cent (σπ/π  < 0.1 )  20853
Distance determined to better than 20 per cent (σπ /π  < 0.2 )  49399
Inferred ratio of external errors to standard errors  ~1.0 - 1.2
Estimated systematic errors in astrometry  < 0.1 mas
Total number of independent astrometric abscissae  ~ 3.6 x 106
Median photometric precision (Hp, for Hp < 9 mag)  0.0015 mag
Mean number of photometric observations per star  110
Total number of Hp photometric measurements  ~13 x 106
Number of entries variable or possibly variable  11597 (8237 new)

Periodic variables

 2712 (970 new)

Cepheid type

 273 (2 new)

RR Lyrae type

 186 (9 new)

δ scuti and SX phoenicis type

 108 (35 new)

Eclipsing binaries (e.g. EA, EB, EW...)

 917 (343 new)

Other types (e.g. M, SR, RV Tau, ..)

 1238 (576 new)

Non-periodic and unsolved (e.g. RCrB, γ Cas, Z And)

 5542 (4145 new)

Not investigated (including micro-variables)

 3343 (3122 new)
   
 Number of solved or suspected double/multiple systems  23882

 Systems with component data (annex part C)

12195 (2996 new)

 Orbital systems (annex part O)

 235

 Astrometric binaries (annes parts G and V)

 2910

 Suspected non-single (including annex part X)

 8542

Tycho Catalogue:

 Number of entries (including 6301 HIP only)  1058332
 Mean sky density  ~ 25 per square degree
 Limiting magnitude  VT ~ 11.5 mag
 Completeness  VT~ 10.5 mag
   
 Median astrometric precision (all stars), J1991.25  25 mas
 Median astrometric precision (VT < 9 mag), J1991.15  7 mas
 Inferred ratio of external errors to standard errors  ~1.0 - 1.5
 Systematic errors in astrometry  < 1 mas
 Mean number of astrometric and photometric observations per star  130
 Total number of astrometric and photometric observations  ~ 130 x 106
 Median photometric precision (all stars): BT, VT, BT - VT  0.07, 0.06, 0.10 mag
 Median photometric precision (VT < 9 mag): BT, VT, B T- VT  0.014, 0.012, 0.019 mag