Hipparcos in the context of Delta Scuti variable

The Geneva Observatory (French: Observatoire de Genève, German: Observatorium von Genf) is an astronomical observatory at Sauverny (CH) in the municipality of Versoix, Canton of Geneva, in Switzerland. It shares its buildings with the astronomy department of the École Polytechnique Fédérale de Lausanne. It has been active in discovering exoplanets, in stellar photometry, modelling stellar evolution, and has been involved in the European Space Agency's Hipparcos, INTEGRAL, Gaia, and Planck missions.

In 1995, the first exoplanet found orbiting a main-sequence star, 51 Pegasi b, was discovered by two scientists of the observatory, Michel Mayor and Didier Queloz, using the radial velocity method with the 1.9-metre telescope at Haute-Provence Observatory in France. Mayor and Queloz were awarded (half of) the Nobel Prize in Physics 2019 for this discovery.

Procyon (/ˈproʊsi.ɒn/) is the brightest star in the constellation of Canis Minor and usually the eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Minoris, which is Latinized to Alpha Canis Minoris, and abbreviated α CMi or Alpha CMi, respectively. As determined by the European Space Agency Hipparcos astrometry satellite, this system lies at a distance of just 11.46 light-years (3.51 parsecs), and is therefore one of Earth's nearest stellar neighbors.

A binary star system, Procyon consists of a white-hued main-sequence star of spectral type F5 IV–V, designated component A, in orbit with a faint white dwarf companion of spectral type DQZ, named Procyon B. The pair orbit each other with a period of 40.84 years and an eccentricity of 0.4.

Brocchi's Cluster (also known as Collinder 399, Cr 399 or Al Sufi's Cluster) is an asterism of 10 stars. Six of the stars appear in a row, across 1.3° of the night sky. The cluster is in the south of the constellation Vulpecula, near the border with Sagitta. Its nickname is the Coathanger. None of these ten stars are believed to be gravitationally bound to each other, thus they are not a star cluster, a fact established by measurements taken by the Hipparcos satellite in 1997. An additional 30 or so much fainter stars are considered by some to be part of the asterism.

Epsilon Pegasi (Latinised from ε Pegasi, abbreviated Epsilon Peg, ε Peg), formally named Enif /ˈiːnɪf/, is the brightest star in the northern constellation of Pegasus.

With an average apparent visual magnitude of 2.4, this is a second-magnitude star that is readily visible to the naked eye. The distance to this star can be estimated using parallax measurements from the Hipparcos astrometry satellite, yielding a value of around 690 light-years (210 parsecs).

The red clump is a clustering of red giants in the Hertzsprung–Russell diagram at around 5,000 K and absolute magnitude (M_V) +0.5, slightly hotter than most red-giant-branch stars of the same luminosity. It is visible as a denser region of the red-giant branch or a bulge towards hotter temperatures. It is prominent in many galactic open clusters, and it is also noticeable in many intermediate-age globular clusters and in nearby field stars (e.g. the Hipparcos stars).

The red clump giants are cool horizontal branch stars, stars originally similar to the Sun which have undergone a helium flash and are now fusing helium in their cores.

The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member is the ~2nd magnitude yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34, and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~560 light-years (172 pc). The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.

The cluster is centered to the northeast of Alpha Persei. It has a core radius of 11.4 ± 1.4 ly, a half-mass radius of 18 ly, and a tidal radius of 70.6 ± 8.5 ly, with 517 members being identified within the latter. The cluster shows solid evidence of having undergone mass segregation, with the mean stellar mass decreasing toward the edge. The age of this cluster is about 50–70 million years. Cluster member stars show a near-solar metallicity, meaning the abundance of elements with atomic numbers higher than 2 are similar to those in the Sun. The cluster shows evidence of tidal tails, which are most likely of galactic origin.

Hamal, pronounced /ˈhæməl/, is a star in the northern zodiacal constellation of Aries. It has the Bayer designation Alpha Arietis, which is Latinized from α Arietis and abbreviated Alpha Ari or α Ari. This star is visible to the naked eye with an apparent visual magnitude of 2.0. Hamal is the brightest star in the constellation and, on average, the 50th-brightest star in the night sky. Based upon parallax measurements made with the Hipparcos astrometry satellite, Hamal is about 65.8 light-years (20.2 parsecs) from Earth. It is drifting closer to the Sun with a radial velocity of −14 km/s.

This is an aging giant star that is likely to host an orbiting planet with a mass greater than Jupiter.

Beta Librae is the brightest star in the zodiac constellation of Libra. It has the proper name Zubeneschamali /zuːˌbɛnɛʃəˈmeɪli/, Beta Librae is its Bayer designation. From parallax measurements taken by the Hipparcos mission, its distance is measured to be 185 light-years (57 parsecs).

The apparent visual magnitude of this star is 2.6. According to Eratosthenes, Beta Librae was observed to be brighter than Antares. Ptolemy, 350 years later, said it was as bright as Antares. The discrepancy may be due to Antares becoming brighter, but this is not known for certain. It could simply be caused by Beta Librae being a variable star, showing a present-day variability of 0.03 of a magnitude.

Fomalhaut (UK: /ˈfɒməloʊt/, US: /ˈfoʊməlhɔːt/) is the brightest star in the southern constellation of Piscis Austrinus, the Southern Fish, and one of the brightest stars in the night sky. It has the Bayer designation Alpha Piscis Austrini, which is an alternative form of α Piscis Austrini, and is abbreviated Alpha PsA or α PsA. This is a class A star on the main sequence approximately 25 light-years (7.7 pc) from the Sun as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.

It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk.

Achernar is the brightest star in the constellation of Eridanus and the ninth-brightest in the night sky. It has the Bayer designation Alpha Eridani, which is Latinized from α Eridani and abbreviated Alpha Eri or α Eri. The name Achernar applies to the primary component of a binary system. The two components are designated Alpha Eridani A (the primary) and B (the secondary), with the latter known informally as Achernar B. As determined by the Hipparcos astrometry satellite, this system is located at a distance of approximately 139 light-years (43 parsecs) from the Sun.

Of the ten brightest stars in the night-time sky by apparent magnitude, Alpha Eridani is the hottest and bluest in color because it is spectral type B. Achernar has an unusually rapid rotational velocity, causing it to become oblate in shape. The secondary is smaller, is spectral type A, and orbits Achernar at a distance of 7.35 AU.