Venus

False colour composite of Venus in visual and ultraviolet wavelengths (from Mariner 10). The surface is completely obscured by clouds.
Size comparison of Venus and Earth
False-colour radar map of Maat Mons
Impact craters on the surface of Venus (false-colour image reconstructed from radar data)
The differentiated structure of Venus
Venus is the second planet from the Sun, orbiting approximately 1.6 times (yellow trail) in Earth's 365 days (blue trail).
Venus, pictured center-right, is always brighter than all other planets or stars as seen from Earth. Jupiter is visible at the top of the image.
The phases of Venus and evolution of its apparent diameter
Transit of Venus, 2004
The pentagram of Venus. Earth is positioned at the centre of the diagram, and the curve represents the direction and distance of Venus as a function of time.
The "black drop effect" as recorded during the 1769 transit
Galileo's discovery that Venus showed phases (although remaining near the Sun in Earth's sky) proved that it orbits the Sun and not Earth.
Modern telescopic view of Venus from Earth's surface
Mockup of the Venera 1 spacecraft
Artist's impression of Mariner 2, launched in 1962: a skeletal, bottle-shaped spacecraft with a large radio dish on top
Global false color view of Venus in ultraviolet radiation done by Mariner 10
180-degree panorama of Venus's surface from the Soviet Venera 9 lander, 1975. Black-and-white image of barren, black, slate-like rocks against a flat sky. The ground and the probe are the focus. Several lines are missing due to a simultaneous transmission of the scientific data.
Venus is portrayed just to the right of the large cypress tree in Vincent van Gogh's 1889 painting The Starry Night.
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Second planet from the Sun and is named after the Roman goddess of love and beauty.

- Venus
False colour composite of Venus in visual and ultraviolet wavelengths (from Mariner 10). The surface is completely obscured by clouds.

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Mercury in true color (by MESSENGER in 2008)

Mercury (planet)

Smallest planet in the Solar System and the closest to the Sun.

Smallest planet in the Solar System and the closest to the Sun.

Mercury in true color (by MESSENGER in 2008)
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Mercury's internal structure and magnetic field
MASCS spectrum scan of Mercury's surface by MESSENGER
Enhanced-color image of Munch, Sander and Poe craters amid volcanic plains (orange) near Caloris Basin
Tolstoj basin is along the bottom of this image of Mercury's limb
Picasso crater — the large arc-shaped pit located on the eastern side of its floor are postulated to have formed when subsurface magma subsided or drained, causing the surface to collapse into the resulting void.
Composite of the north pole of Mercury, where NASA confirmed the discovery of a large volume of water ice, in permanently dark craters that are found there.
Graph showing relative strength of Mercury's magnetic field
After one orbit, Mercury has rotated 1.5 times, so after two complete orbits the same hemisphere is again illuminated.
Image mosaic by Mariner 10, 1974
False-color map showing the maximum temperatures of the north polar region
False-color image of Carnegie Rupes, a tectonic landform—high terrain (red); low (blue).
Mercury, from Liber astronomiae, 1550
Ibn al-Shatir's model for the appearances of Mercury, showing the multiplication of epicycles using the Tusi couple, thus eliminating the Ptolemaic eccentrics and equant.
Transit of Mercury. Mercury is visible as a black dot below and to the left of center. The dark area above the center of the solar disk is a sunspot.
Elongation is the angle between the Sun and the planet, with Earth as the reference point. Mercury appears close to the Sun.
Water ice (yellow) at Mercury's north polar region
MESSENGER being prepared for launch
Mercury transiting the Sun as viewed by the Mars rover Curiosity (June 3, 2014).
Mariner 10, the first probe to visit Mercury
Estimated details of the impact of MESSENGER on April 30, 2015

Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°.

The terrestrial planets of the Solar System: Mercury, Venus, Earth and Mars, sized to scale

Terrestrial planet

Planet that is composed primarily of silicate rocks or metals.

Planet that is composed primarily of silicate rocks or metals.

The terrestrial planets of the Solar System: Mercury, Venus, Earth and Mars, sized to scale
Relative masses of the terrestrial planets of the Solar System, and the Moon (shown here as Luna)
The inner planets (sizes to scale). From left to right: Earth, Mars, Venus and Mercury.
Sizes of Kepler planet candidates based on 2,740 candidates orbiting 2,036 stars as of 4 November 2013 (NASA).
Artist's impression of a carbon planet
Geysers erupting on Enceladus

Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth and Mars.

Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black)

Retrograde and prograde motion

Object in the direction opposite the rotation of its primary, that is, the central object .

Object in the direction opposite the rotation of its primary, that is, the central object .

Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black)
The orange moon is in a retrograde orbit.

Except for Venus and Uranus, planetary rotations are also prograde.

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Sun

Star at the center of the Solar System.

Star at the center of the Solar System.

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Illustration of the Sun's structure, in false color for contrast
Illustration of a proton-proton reaction chain, from hydrogen forming deuterium, helium-3, and regular helium-4.
Illustration of different stars's internal structure, the Sun in the middle has an inner radiating zone and an outer convective zone.
High-resolution image of the Sun's surface taken by the Daniel K. Inouye Solar Telescope (DKIST)
During a total solar eclipse, the solar corona can be seen with the naked eye, during the brief period of totality.
The Sun's transition region taken by Hinode's Solar Optical Telescope
Sunlight and glare seen overlooking from the International Space Station
Once outside the Sun's surface, neutrinos and photons travel at the speed of light
Visible light photograph of sunspot
Measurements from 2005 of solar cycle variation during the previous 30 years
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The size of the current Sun (now in the main sequence) compared to its estimated size during its red-giant phase in the future
The Solar System, with sizes of the Sun and planets to scale. The terrestrial planets are on the right, the gas and ice giants are on the left.
The Trundholm sun chariot pulled by a horse is a sculpture believed to be illustrating an important part of Nordic Bronze Age mythology.
Sol, the Sun, from a 1550 edition of Guido Bonatti's Liber astronomiae.
False-color image taken in 2010 as seen in 30.4-nanometer ultraviolet light wavelength
A false-color of a coronal hole on the Sun forming a question mark (22 December 2017)
A false-color solar prominence erupts in August 2012, as captured by the Solar Dynamics Observatory
The Sun seen from Earth, with glare from the lenses. The eye also see glare when looked towards the Sun directly.
Sun and Immortal Birds Gold Ornament by ancient Shu people. The center is a sun pattern with twelve points around which four birds fly in the same counterclockwise direction, Shang dynasty

It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable – but not for about five billion years.

The planet Mars has an atmosphere composed of thin layers of gases.

Atmosphere

Layer of gas or layers of gases that envelope a planet, and is held in place by the gravity of the planetary body.

Layer of gas or layers of gases that envelope a planet, and is held in place by the gravity of the planetary body.

The planet Mars has an atmosphere composed of thin layers of gases.
The atmospheric gases around Earth scatter blue light (shorter wavelengths) more than light toward the red end (longer wavelengths) of the visible spectrum; thus, a blue glow over the horizon is seen when observing Earth from outer space.
A diagram of the layers of Earth's atmosphere
Graphs of escape velocity against surface temperature of some Solar System objects showing which gases are retained. The objects are drawn to scale, and their data points are at the black dots in the middle.

The atmospheres of the planets Venus and Mars are principally composed of carbon dioxide and nitrogen, argon and oxygen.

Greenhouse gases allow sunlight to pass through the atmosphere, heating the planet, but then absorb and re-radiate the infrared radiation (heat) the planet emits

Greenhouse effect

"Heating of the earth" redirects here.

"Heating of the earth" redirects here.

Greenhouse gases allow sunlight to pass through the atmosphere, heating the planet, but then absorb and re-radiate the infrared radiation (heat) the planet emits
Quantitative analysis: Energy flows between space, the atmosphere, and Earth's surface, with greenhouse gases in the atmosphere absorbing and emitting radiant heat, forming Earth's energy balance.
The greenhouse effect and its impact on climate were succinctly described in this 1912 Popular Mechanics article meant for reading by the general public.
The solar radiation spectrum for direct light at both the top of Earth's atmosphere and at sea level
Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in longer wavelengths (12–15 micrometers) that water vapor does not, partially closing the "window" through which heat radiated by the surface would normally escape to space. (Illustration NASA, Robert Rohde)
Earth's rate of heating (graph) is a result of factors which include the enhanced greenhouse effect.
The Keeling Curve of atmospheric CO2 abundance.
A modern greenhouse in RHS Wisley

A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into the atmosphere, as happened with carbon dioxide and water vapor on Venus.

Sagan in 1980

Carl Sagan

American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator.

American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator.

Sagan in 1980
Sagan in Rahway High School's 1951 yearbook
Sagan in University of Chicago's 1954 yearbook
Sagan in Cosmos (1980)
Carl Sagan popularized the Cosmic Calendar as a method to visualize the chronology of the universe, scaling its current age of 13.8 billion years to a single year in order to help intuit it for pedagogical purposes.
The Planetary Society members at the organization's founding. Sagan is seated on the right.
Pale Blue Dot: Earth is a bright pixel when photographed from Voyager 1, 6 e9km away. Sagan encouraged NASA to generate this image.
Sagan admitted that he had overestimated the danger posed by the 1991 Kuwaiti oil fires.
The United States and Soviet Union/Russia nuclear stockpiles, in total number of nuclear bombs/warheads in existence throughout the Cold War and post-Cold War era
Sagan in 1987
Sagan (center) speaks with CDC employees in 1988.
Stone dedicated to Sagan in the Celebrity Path of the Brooklyn Botanic Garden
NASA Distinguished Public Service Medal

Sagan argued the hypothesis, accepted since, that the high surface temperatures of Venus can be attributed to, and calculated using, the greenhouse effect.

Magellan (spacecraft)

The Voyager probe spacecraft bus that formed the main body of Magellan
Thrusters, Star 48 booster and the internal components of the Forward Equipment Module
Positions of the three antennas
Mosaic of the "left-looking" data collected during cycle 1
Mosaic of the "right-looking" data collected during cycle 2
Five global views of Venus by Magellan
A poster designed for the Magellan end of mission
alt=Annotated diagram of Magellan|Annotated diagram of Magellan
alt=Magellan during pre-flight checkout|Magellan during pre-flight checkout
alt=Magellan with its Star 48B solid rocket motor undergoing final checks at the Kennedy Space Center|Magellan with its Star 48B solid rocket motor undergoing final checks at the Kennedy Space Center
alt=Magellan being fixed into position inside the payload bay of Atlantis prior to launch|Magellan being fixed into position inside the payload bay of Atlantis prior to launch
alt=Launch of STS-30 on May 4, 1989|Launch of STS-30 on May 4, 1989
The spacecraft in a deployment position in Atlantis' payload bay
alt=Deployment of Magellan with Inertial Upper Stage booster|Deployment of Magellan with Inertial Upper Stage booster
alt=Trajectory of Magellan to Venus|Trajectory of Magellan to Venus
alt=Mosaic of the stereo data collected during cycle 3|Map of the stereo imaging collected by Magellan during cycle 3
alt=Eistla Regio featuring Gula Mons reprojected in 3D from stereo data|Eistla Regio featuring Gula Mons reprojected in 3D from stereo data
alt=Reprojection of Maat Mons|Reprojection of Maat Mons, with vertical exaggeration
alt=Volcanic dome observed from reprojecting stereo data|Volcanic dome in Alpha Regio observed from reprojecting stereo data
alt=Maxwell Montes, highest point on Venus|Maxwell Montes, highest point on Venus
alt=Coronae as seen in the Fortuna region of Venus|Volcanoes as seen in the Fortuna region of Venus
alt=Aphrodite Terra, a rugged landscape|Aphrodite Terra, a rugged landscape
alt=Addams crater|Addams crater
alt=Pancake domes visible in Alpha Regio|Pancake domes visible in Alpha Regio
alt=A meandering lava channel from Fortuna Tessera to Sedna Planitia|A meandering lava channel from Fortuna Tessera to Sedna Planitia
alt=An unusual volcanic edifice in the Eistla region|An unusual volcanic edifice in the Eistla region
alt=175-kilometer Isabella crater|175-kilometer Isabella crater

The Magellan spacecraft was a 1035 kg robotic space probe launched by NASA of the United States, on May 4, 1989, to map the surface of Venus by using synthetic-aperture radar and to measure the planetary gravitational field.

The naked eye

Naked eye

Practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection.

Practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection.

The naked eye
A photographic approximation of a naked eye view of the night sky from a small rural town (top) and a metropolitan area (bottom). Light pollution dramatically reduces the visibility of stars.
The Milky Way is visible over the Very Large Telescope, demonstrating clear atmosphere above Paranal Observatory.

During daylight only the Moon and Sun are obvious naked eye objects, but in many cases Venus can be spotted in daylight and in rarer cases Jupiter.

Figure 1. Carbon dioxide pressure-temperature phase diagram

Supercritical fluid

Any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid.

Any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid.

Figure 1. Carbon dioxide pressure-temperature phase diagram
Figure 2. Carbon dioxide density-pressure phase diagram
A black smoker, a type of hydrothermal vent

Supercritical fluids occur in the atmospheres of the gas giants Jupiter and Saturn, the terrestrial planet Venus, and probably in those of the ice giants Uranus and Neptune.