Venus taken by Mariner 10

Venus, taken by Mariner 10 in 1974     [Source]

After the Moon, Venus is the brightest permanent object in the night sky. Sometimes referred to as the “Morning Star” or “Evening Star”, it never appears to achieve a separation greater than 48 degrees from the Sun due to its status as an inner planet. Like Mercury, it has no natural satellites of its own.

To an experienced observer, it can be spotted without optical aid even during broad daylight! Venus is at its brightest during its crescent phase, rather than when fully illuminated. This is because its apparent illuminated surface area is largest when closest to Earth (i.e. a large crescent versus a tiny circular disk).

Venus orbits the Sun once every 225 Earth days, about two-thirds of Earth’s orbital period. It features the most circular orbit amongst the planets. However, its rotation has been found to be like no other planet in the Solar System: it is in reverse! To an observer on Venus, the Sun would slowly appear to rise in the west and eventually set in the east.

Venus would make for a miserable habitat; its surface pressure is nearly 100 times that of Earth. With an average surface temperature of of 462°C (863°F), it is the hottest planet in the Solar System. The volcanic surface of the planet is shrouded by its dense atmosphere filled with clouds of sulfuric acid (H2SO4). As a result, Venus’ surface cannot be observed in the visible spectrum. (From the surface, not even the Sun would be distinguishable in the Venusian sky!)

Not only does Venus exhibit phases, but also a drastic change in apparent size as it orbits alongside Earth

Not only does Venus exhibit phases, but also a drastic change in apparent size as it orbits alongside Earth     [Source]

However, observing Venus is not without reward. Even with a small telescope, one can relive the one of Galileo’s most important discoveries: the phases of Venus. Along with his discovery of Jupiter‘s four largest moons, it produced the strongest evidence against the geocentric (Earth-centered) model for the Solar System. If Venus actually orbited Earth, its apparent proximity to the Sun would never allow it to exhibit any phase other than that of a crescent.


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