Crash Course Astronomy: Venus

Venus was named after the Roman goddess of love.
Known for its stunning beauty, especially noticeable at twilight when it shines brightly like a diamond.
Despite its beauty, it is often described as a hellish place.

Second planet from the Sun, closer to the Sun than Earth.
Third brightest natural object in the sky after the Sun and Moon.
Can be confused for an airplane due to its brightness; sometimes reported as a UFO.
Maximum angle from the Sun is approximately 45°.
Optimal viewing is after sunset or before sunrise.
Exhibits phases similar to the Moon, observable through a telescope. Venus exhibits phases like the Moon, including full, gibbous, half, and crescent phases. Its closest approach to Earth is about 45 million kilometers away, and it appears brighter during its crescent phase despite showing less illuminated surface.

Similar to the moon, it goes through phases as it orbits the Sun:
- Full phase: when on the far side of its orbit from Earth.
- Gibbous: as it approaches Earth.
- Half: at the halfway point.
- Crescent: when it is between the Earth and Sun.
Closest approach to Earth: about 45 million kilometers away.
During the crescent phase, it appears brighter despite showing less illuminated surface.

During a transit, Venus appears as a small black circle crossing the Sun.
Significance of transits in history:
- Allowed scientists to calculate the distance to Venus and use it to measure the solar system.
- Historical expeditions were organized to observe transits.
Rare occurrences, happening in pairs every eight years, but separated by over a century (last transits in 2004 and 2012).
Next transit is expected on December 10, 2117.

Exceptionally bright due to a thick cloud layer composed of sulfuric acid, reflecting almost all sunlight.
This layer makes Venus appear as a nearly featureless white disk.

Size:
- Diameter: approximately 12,100 kilometers (about 95% the width of Earth).
- Mass: around 80% that of Earth.
Distance from the Sun:
- Roughly 110 million kilometers (about two-thirds the distance of Earth from the Sun).
Surface Conditions:
- Average surface temperature: 460°C (860°F).
- Atmosphere is mainly carbon dioxide with a pressure 90 times that of Earth's.
- Experiences extreme conditions, including acid rain (sulfuric acid) which evaporates before reaching the ground.

Venus's extreme heat is attributed to a runaway greenhouse effect:
1. In earlier times, Venus may have had a more temperate climate and liquid water oceans.
2. As the Sun aged and warmed, the oceans evaporated, increasing atmospheric water vapor—a potent greenhouse gas.
3. As temperatures rose, carbon dioxide dissolved in water was released, further heating the planet and thickening the atmosphere.
4. Over time, heat led to CO2 being released from rocks, exacerbating the greenhouse effect.
Absence of a magnetic field means there’s no protection from the solar wind, resulting in the loss of lighter atmospheric elements and water over billions of years.

Speculated that Venus might experience something akin to snow, but it wouldn't be water ice.
Possible metallic snow from minerals like bismuthinite and galena, vaporized by heat and deposited on cooler mountaintops.
Venus has an extremely slow rotation, with one day lasting about 243 Earth days, causing unique day-night cycles.
Retrograde motion: Venus rotates backwards, reversing its north and south poles; origin of this motion remains unclear.

Inhabitability would be strange:
- Thick atmosphere creates twilight-like brightness across the planet.
- Consistent surface temperature due to atmospheric thickness and long day/night cycles.
- The Sun would rise in the west due to retrograde rotation.
No moons; any former moon likely lost to solar gravity effects.
Venus is the most spherical planet due to its slow rotation, which prevents equatorial bulging.

Little is known about its interior, but similarities to Earth suggest a possible core, mantle, and crust.
Lack of tectonic activity; surface features indicate a relatively young age (about half a billion years).
Approximately 1,000 impact craters distributed evenly, suggesting a significant resurfacing event possibly caused by volcanic activity.

Volcano Count:
- 167 volcanoes larger than 100 km discovered, indicating extensive volcanic activity.
Evidence suggests ongoing volcanic activity; for instance, abnormally warm regions indicating potential magma.

Possible “pancake domes” created by slow, viscous lava flow that spreads out over large areas.
The international naming convention for surface features reflects cultural homage to women and goddesses.

Final insights:
- Venus is comparable to Earth in size but is inhospitable due to a super thick atmosphere.
- The hottest planet in the solar system, attributable to greenhouse effects.
- Slowest planetary rotation, retrograde motion, and significant geological history marked by volcanic activity.

This episode is part of the Crash Course Astronomy series produced in association with PBS Digital Studios, written by Phil Plait.
Script edited by Blake de Pastino, with consulting from Dr. Michelle Thaller.
Co-directed by Nicholas Jenkins and Michael Aranda, with editing by Nicole Sweeney and graphics by Thought Café.