Venus occults the star Regulus. This rare event is used to determine the diameter of Venus and the structure of the Venusian atmosphere.
Regulus is the brightest object in the constellation Leo and one of the brightest stars in the night sky. It has the Bayer designation designated Leonis, which is Latinized to Alpha Leonis, and abbreviated Alpha Leo or Leo. Regulus appears singular, but is actually a quadruple star system composed of four stars that are organized into two pairs. The spectroscopic binary Regulus A consists of a blue-white main-sequence star and its companion, which has not yet been directly observed, but is probably a white dwarf. The system lies approximately 79 light years from the Sun.
HD 87884 is separated from Regulus by 176 and is itself a close pair. Regulus, along with five slightly dimmer stars (Zeta Leonis, Mu Leonis, Gamma Leonis, Epsilon Leonis, and Eta Leonis) have collectively been called 'the Sickle', which is an asterism that marks the head of Leo.
Venus is the second planet from the Sun. It is named after the Roman goddess of love and beauty. As the brightest natural object in Earth's night sky after the Moon, Venus can cast shadows and can be visible to the naked eye in broad daylight. Venus's orbit is smaller than that of Earth, but its maximal elongation is 47°; thus, it can be seen not only near the Sun in the morning or evening, but also a couple of hours before or after sunrise or sunset, depending on the observer's latitude and on the positions of Venus and the Sun. Most of the time, it can be seen either in the morning or in the evening. At some times, it may even be seen a while in a completely dark sky. Venus orbits the Sun every 224.7 Earth days. It has a synodic day length of 117 Earth days and a sidereal rotation period of 243 Earth days. Consequently, it takes longer to rotate about its axis than any other planet in the Solar System, and does so in the opposite direction to all but Uranus. This means that the Sun rises from its western horizon and sets in its east. Venus does not have any moons, a distinction it shares only with Mercury among the planets in the Solar System.Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is about 92 times the sea level pressure of Earth, or roughly the pressure at 900 m (3,000 ft) underwater on Earth. Even though Mercury is closer to the Sun, Venus has the hottest surface of any planet in the Solar System, with a mean temperature of 737 K (464 °C; 867 °F). Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in light. It may have had water oceans in the past, but these would have vaporized as the temperature rose under a runaway greenhouse effect. The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field.As one of the brightest objects in the sky, Venus has been a major fixture in human culture for as long as records have existed. It has been made sacred to gods of many cultures and has been a prime inspiration for writers and poets as the "morning star" and "evening star". Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BC.Its proximity to Earth has made Venus a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft (Venera 1 in 1961) and the first to be successfully landed on (by Venera 7 in 1970). The planet's thick clouds render observation of its surface impossible in the visible spectrum, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more complex missions, but they are hindered by Venus's hostile surface conditions. The possibility of life on Venus has long been a topic of speculation; in recent years, the topic has received active research.