Ancient astronomers didn’t really know what Venus was. They knew it was an object that moved in the sky from night to night, sometimes being obscured by the glare of the Sun. But it wasn’t until Copernicus developed his model of the Solar System that

placed the Sun at the center, and the planets orbiting it. At that point, both Venus and Earth were recognized to be planets.

Galileo pointed his telescope at Venus in 1610, and confirmed Copernicus’ theory by showing that Venus went through distinct phases, just like the Moon. The phases matched the predictions made by Copernicus, and demonstrated that Venus was really a

planet, orbiting the Sun and not the Earth.

This model was confirmed even more when Venus made a transit across the surface of the Sun on December 4, 1639. The most

recent transit of Venus happened in 2004, and the next one will occur in 2012.

WHO DISCOVERED VENUS?

Venus is a beautiful planet at night. It is one of the brightest objects in the night sky. Only the moon is brighter

WHY VENUS?

• Venus is very bright in the sky “Evening star” “Morning star”

Fun Fact!

The ancients named Venus after the goddess of love and beauty because it

is the brightest planet.

Early civilizations thought Venus was two different bodies, called Phosphorus and

Hesperus by the Greeks, and Lucifer and Vesper by the Romans. This is because

when its orbit around the Sun overtakes Earth’s orbit, it changes from being visible after sunset to being visible before sunrise.

Mayan astronomers made detailed observations of Venus as early as 650 AD.

MORNING STAR AND THE EVENING STAR

THE PLANET VENUS

• Venus is the planet nearest to Earth, sometimes approaching to within 40 million km

• The orbit of Venus is nearly circular at a distance of 108 million km (0.72 AU)

• Venus can get as close as 40 million km from the Earth. This is called an inferior conjunction every 584 days, on average.

Mass: 4,867,320,000,000,000 billion kg (0.815 x Earth)Equatorial Diameter: 12,104 kmPolar Diameter: 12,104 kmEquatorial Circumference: 38,025 kmKnown Satellites: noneNotable Satellites: noneOrbit Distance: 108,209,475 km (0.73 AU)Orbit Period: 224.70 Earth daysSurface Temperature: 462 °CFirst Record: 17th century BCRecorded By: Babylonian astronomers

PLANET PROFILE

Venus looks very bright to the naked eye and even a

small telescope shows that Venus goes through phases

like the MoonThe surface of Venus is

always obscured by a very dense cloud cover

Reflects 70% of the sunlight

Various bands are visible in different wavelength light

APPEARANCE OF VENUS

Enhanced picture of Venus shot through a violet filter by the Galileo spacecraft

Venus appears to go through phasesDifferent from Moon because distance changes drastically

PHASES OF VENUS

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12,102 km in diameter(12,756 km

for Earth) 82% the mass

of Earth Similar density,

5.3 g/cm3 (5.5 g/cm3 for Earth)

Venus takes 2,243days to

rotate on it axis and it rotates the opposite direction

of Earth

Venus is nearly the same size as Earth Venus takes 223

days to orbit the Sun

BASIC PROPERTIES OF VENUS

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The atmosphere of Venus causes a very high surface temperature and gives the surface a perpetual red twilightThe weather at the surface is hot, dry, calmThe pressure at the surface is 90 times the Earth’s atmospheric pressure

THE ATMOSPHERE OF VENUS

Gas %Carbon Dioxide (CO2)

95.3

Nitrogen (N2)

2.7

Argon (Ar)

1.6

Oxygen (O2)

0.15

Neon (Ne)

0.0003

The surface temperature of Venus is 700 K

800 degrees FahrenheitCaused by the greenhouse effect

Venus has 1 million times more CO2 than Earth

Sunlight that diffuses through the atmosphere heats the surface and the CO2 acts as a blanket

The surface heats up until the radiation of heat is the same as the absorption of heat from the SunThe dense atmosphere makes the temperature the same everywhere on the surface of Venus

Little weather

SURFACE TEMPERATURE OF VENUS

The first successful flyby of the Planet Venus was accomplished by Mariner 2 in 1962.

In 1970, the Soviet Venera 7 lander became the first probe to return data from the surface of Venus. Later Venera landers would

return images from the surface.

America sent two spacecraft to the planet in 1978. The Pioneer Venus Orbiter went into orbit around the planet, while the Pioneer Venus Multi-Probe deployed four atmospheric entry

probes to investigate the atmosphere.

The twin Vega spacecraft each deployed a surface lander and an instrumented atmospheric balloon in 1985.

The American Magellan mission, launched on the Space Shuttle in 1989, used a radar system to create high-resolution maps of the

planets surface.

Launched in 2005, the European Venus Express mission continues to orbit the planet.

THE EXPLORATION OF VENUS

The Magellan mission to Venus was launched May 4, 1989 and arrived at Venus on August 10, 1990Magellan used high resolution radar to map the

surface of Venus through the opaque cloudsMagellan worked for 4 years and mapped 98% of

the surface of Venus

THE MAGELLAN MISSION TO VENUS

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False color picture of Venus constructed from radar images from the Magellan space craft

The Magellan data can be processed into 3-D views of the surface of Venus

THE SURFACE OF VENUS

3-D view of three impact crater on the surface of Venus

The largest crater on Venus is the Mead Crater

CRATERS ON THE SURFACE OF VENUS

The Mead Crater - 280 km in diameter

Larger than the largest crater on Earth

Computer generated 3-D view of Sif Mons using data from Magellan

Venus is a planet with wide-scale volcanic activityIn the lowland plains, lava renews the surface and erases cratersThere are many volcanoes associated with surface hot spots

VOLCANOES ON VENUS

• The largest volcano on Venus is Sif Mons

3 km high, 500 km across

Caldera is 40 km across

• These volcanoes result from magma reaching the surface

• Pressure under the surface can cause bulges called coronae

Venus rotates counter-clockwise:Also known as retrograde rotation. A possible reason might be a collision in the past with an asteroid or other object that caused the planet to alter its rotational path. It also differs from most other planets in our solar system by having no natural satellites.

FACTS ABOUT VENUS

www.scientificamerican.comwww.universetoday.com

www.space-facts.comwww.historicspacecraft.com

REFERENCES

LECTURE 11

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