Venus - Observation


Venus is always brighter than any star (apart from the Sun). The greatest luminosity, apparent magnitude −4.9, occurs during crescent phase when it is near the Earth. Venus fades to about magnitude −3 when it is backlit by the Sun. The planet is bright enough to be seen in a mid-day clear sky, and the planet can be easy to see when the Sun is low on the horizon. As an inferior planet, it always lies within about 47° of the Sun.

Venus "overtakes" the Earth every 584 days as it orbits the Sun. As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. While Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported "unidentified flying object". U.S. President Jimmy Carter reported having seen a UFO in 1969, which later analysis suggested was probably the planet. Countless other people have mistaken Venus for something more exotic.

As it moves around its orbit, Venus displays phases in a telescopic view like those of the Moon: In the phases of Venus, the planet presents a small "full" image when it is on the opposite side of the Sun. It shows a larger "quarter phase" when it is at its maximum elongations from the Sun, and is at its brightest in the night sky, and presents a much larger "thin crescent" in telescopic views as it comes around to the near side between the Earth and the Sun. Venus is at its largest and presents its "new phase" when it is between the Earth and the Sun. Its atmosphere can be seen in a telescope by the halo of light refracted around the planet.

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