Gaia Universe model snapshot - A statistical analysis of the expected contents of the Gaia catalogue

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Table 28

Comparison of Hipparcos and Gaia characteristics and the predicted number of stars, variables, and binaries presented in this study.

	Hipparcos	Gaia

Number of stars	118 218	1 100 000 000^a
Mean sky density (per square degree)	~3	~30.425
Limiting magnitude	V ~ 12.4 mag	V ~ 20–25 mag
Median astrometric precision	0.97 mas (V < 9)	~10 μ as (V = 15)
Possibly variable	11 597	21 500 000^a
Suspected double systems	23 882	410 000 000^a

Notes.

^(a)

Includes stars that may not be resolved owing to their angular separation and Gaia’s resolution power.

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