Venus, the brightest object in our sky after the Sun and Moon, has captivated observers for millennia. Often called the “morning star” or “evening star” due to its visibility just before dawn or after dusk, its “discovery” was not a single event. Instead, it was a gradual unveiling of its true nature as a planet, evolving from ancient observations to modern exploration.
Venus in Ancient Times
Ancient civilizations across the globe observed Venus. The Babylonians, as early as 1600 BCE, documented its appearances on clay tablets, associating it with their goddess Ishtar. Similarly, the Maya civilization considered Venus a highly important celestial body, calling it Chac Ek or Noh Ek’, “the Great Star.” They tracked its complex cycles with precision, even timing wars based on its positions, as recorded in the Dresden Codex.
The ancient Greeks initially perceived Venus as two distinct entities: Phosphoros, the morning star, and Hesperos, the evening star. However, early Greek mathematicians, such as Pythagoras, recognized these were the same object. The Romans later adopted Greek mythology, identifying the planet with their goddess of love, beauty, and fertility, Venus. These early observations, made without optical aid, did not reveal Venus’s planetary characteristics or its orbit around the Sun.
Galileo’s Telescopic Revelations
The understanding of Venus changed significantly in 1610, when Galileo Galilei observed the planet with his improved telescope. He noticed Venus exhibited a full set of phases, much like Earth’s Moon, transitioning from a thin crescent to a full disk. This observation contradicted the prevailing geocentric, or Earth-centered, model of the universe proposed by Ptolemy.
In the Ptolemaic system, Venus was thought to orbit Earth on an epicycle, allowing only a limited range of phases. Galileo’s discovery of a complete cycle of phases, including a nearly full Venus when it was on the far side of the Sun, provided evidence for the heliocentric model, where Venus orbits the Sun. This direct visual proof supported Nicolaus Copernicus’s theory that planets revolve around the Sun, altering humanity’s perception of the solar system. Galileo’s findings unveiled Venus’s true orbital behavior.
Further Unveiling Through Observation
Following Galileo’s work, astronomers continued to observe Venus telescopically. Transits of Venus, when the planet passes directly between the Sun and Earth, became important. Observers like Jeremiah Horrocks in 1639 and later expeditions, including those led by James Cook, used these transits to calculate the distance from Earth to the Sun, determining the solar system’s scale.
In 1761, during another transit of Venus, Russian polymath Mikhail Lomonosov observed a luminous ring or halo around the planet’s silhouette. He correctly inferred this phenomenon was caused by sunlight refraction through a dense atmosphere. This provided the first hint of Venus’s atmospheric characteristics. Despite these advances, the planet’s thick cloud cover prevented direct visual observation of its surface, keeping many mysteries hidden.
Modern Planetary Exploration
The mid-20th century began a new era of Venus exploration with space probes, revealing its physical environment. NASA’s Mariner 2, launched in 1962, became the first spacecraft to perform a planetary flyby, passing within approximately 34,800 kilometers of Venus. This mission provided initial data confirming Venus’s extremely hot surface temperature, around 425°C, and its primarily carbon dioxide atmosphere.
The Soviet Union’s Venera program (1961-1984) achieved numerous milestones. Venera 3 (1966) was the first human-made object to impact another planet’s surface. Venera 7 (1970) made the first soft landing and transmitted data from the surface. Subsequent Venera missions, like Venera 9 (1975), provided the first black and white images of the Venusian surface, revealing a desolate, rocky landscape.
NASA’s Magellan mission, launched in 1989, significantly advanced understanding of Venus’s topography. Equipped with synthetic aperture radar, Magellan penetrated the thick clouds and mapped over 98% of Venus’s surface with high resolution (1990-1994). This mission created the first detailed global radar maps, revealing extensive volcanic plains, large continents, and unique geological features, providing a detailed view of the planet’s hidden terrain. These robotic missions provided the most thorough understanding of Venus’s extreme conditions and geology.