Mercury is the densest planet (5.4 times the density of water) and the closest planet to the Sun. Mercury was last visited by the Mariner 10 spacecraft in 1974.

The basics

Order (outwards from the Sun): 1
Average distance from the Sun: 57 900 000 km (0.39 astronomical units)
Period of revolution (length of year): 87.95 days
Period of rotation (length of day): 58.6 days
Diameter: 4 879 km
Surface gravity: 0.38 times greater than Earth’s
Atmosphere: Virtually none
Satellites: None
Composition: Basaltic rocks and dust; nickel-iron core
Surface temperature: Average 227 degrees Celsius during the day, -173 degrees Celsius at night

Appearance of surface

Rocky and covered with meteorite craters. Appearance similar to Earth’s Moon.

Appearance in Earth’s sky

Mercury is visible to the unaided eye, and appears as a bright star-like object. In the northern hemisphere, Mercury stays close to the glow of dusk and dawn, either very low in the west after sunset, or very low in the east before sunrise. In the Read More

Mercury is the densest planet (5.4 times the density of water) and the closest planet to the Sun. Mercury was last visited by the Mariner 10 spacecraft in 1974.

The basics

Order (outwards from the Sun): 1
Average distance from the Sun: 57 900 000 km (0.39 astronomical units)
Period of revolution (length of year): 87.95 days
Period of rotation (length of day): 58.6 days
Diameter: 4 879 km
Surface gravity: 0.38 times greater than Earth’s
Atmosphere: Virtually none
Satellites: None
Composition: Basaltic rocks and dust; nickel-iron core
Surface temperature: Average 227 degrees Celsius during the day, -173 degrees Celsius at night

Appearance of surface

Rocky and covered with meteorite craters. Appearance similar to Earth’s Moon.

Appearance in Earth’s sky

Mercury is visible to the unaided eye, and appears as a bright star-like object. In the northern hemisphere, Mercury stays close to the glow of dusk and dawn, either very low in the west after sunset, or very low in the east before sunrise. In the southern hemisphere, Mercury is high enough above the horizon that it can be viewed in total darkness several times a year.

Telescopic appearance

Mercury is hard to observe because it is usually close to the horizon, where it’s obscured by atmospheric turbulence. Because it is closer to the Sun than the Earth, Mercury shows phases, like the Moon. It is unlikely you will see any surface details on Mercury.


© Canadian Heritage Information Network, 2003

Mercury

Mercury is the densest planet (5.4 times the density of water) and the closest planet to the Sun. Mercury was last visited by the Mariner 10 spacecraft in 1974.

NASA / JPL

© NASA / JPL


Venus is the hottest planet in the solar system

Venus is the hottest planet in the solar system because the constant cloud cover traps heat like a greenhouse. In 1975, the Soviet Venera probes landed on Venus, sending back TV pictures of the surface. In 1992, NASA’s Magellan went into a Venus orbit and produced a complete radar picture of the surface.

Venus spins in the opposite direction of every other planet. This means that, on Venus, the Sun rises in the west and sets in the east.

The basics

Order (outwards from the Sun): 2
Average distance from the Sun: 108 200 000 km (0.72 astronomical units)
Period of revolution (length of year): 224.70 days
Period of rotation (length of day): 243.02 days
Diameter: 12 104 km
Surface gravity: 0.91 times greater than Earth’s
Atmosphere: Carbon dioxide, hydrogen sulphide, sulphuric acid, 90 times thicker than Earth’s atmosphere. Dense clouds completely cover the planet. Constant lightning.
Satellites: None
Composition: Basaltic and granitic (hard volcanic) rocks
Surface temperature: 460 degrees Celsius both da Read More

Venus is the hottest planet in the solar system

Venus is the hottest planet in the solar system because the constant cloud cover traps heat like a greenhouse. In 1975, the Soviet Venera probes landed on Venus, sending back TV pictures of the surface. In 1992, NASA’s Magellan went into a Venus orbit and produced a complete radar picture of the surface.

Venus spins in the opposite direction of every other planet. This means that, on Venus, the Sun rises in the west and sets in the east.

The basics

Order (outwards from the Sun): 2
Average distance from the Sun: 108 200 000 km (0.72 astronomical units)
Period of revolution (length of year): 224.70 days
Period of rotation (length of day): 243.02 days
Diameter: 12 104 km
Surface gravity: 0.91 times greater than Earth’s
Atmosphere: Carbon dioxide, hydrogen sulphide, sulphuric acid, 90 times thicker than Earth’s atmosphere. Dense clouds completely cover the planet. Constant lightning.
Satellites: None
Composition: Basaltic and granitic (hard volcanic) rocks
Surface temperature: 460 degrees Celsius both day and night, due to greenhouse effect caused by heavy cloud cover

Appearance of surface

Landscapes of rocky rubble or flat rock outcrops. The rocks are partially molten and flow slowly. Light level similar to an overcast day on Earth.

Appearance in Earth’s sky

A brilliant star-like object seen as a ""morning star"" or ""evening star."" Always appears close to the Sun in the sky. Venus outshines every other object in the sky except the Sun and Moon. It is often misidentified as an aircraft or an unidentified flying object (UFO) because of its striking brilliance.

Telescopic appearance

Thick clouds make it impossible to see the surface of Venus, but the phases (similar to Mercury’s and the Moon’s) are easily seen with any telescope. Even in a thin crescent phase, Venus is large enough that the phase can be seen with binoculars.


© Canadian Heritage Information Network, 2003

Venus

Venus is the hottest planet in the solar system because the constant cloud cover traps heat like a greenhouse.

NASA / JPL

© NASA / JPL


Venus

The surface of Venus

NASA / JPL

© NASA / JPL


Earth is unique in the solar system. It is the only planet that has both liquid water and an oxygen-nitrogen atmosphere, two features essential to life as we know it. It is also the only planet known to harbour living creatures. There are over six billion people on Earth now, and countless animals and plants.

As the Earth orbits the Sun it also rotates on its axis. When we’re facing the Sun it’s daytime, and when we’re facing away it’s night. Because the Earth rotates on its axis as it orbits the Sun, parts of the Earth that face the Sun experience daytime while parts that face away experience night. Though the Earth rotates once every 23 hours 56 minutes, the period from one sunrise to the next is actually 24 hours. That’s because the Earth changes position from one day to the next as it moves around the Sun. As a result, it must rotate for an additional 4 minutes to bring the Sun back to the same position in the sky.

Because the Earth rotates on its axis as it orbits the Sun, parts of the Earth that face the Sun experience daytime while parts that face away experience night. Though the Earth rotates once every 23 hours 56 Read More

Earth is unique in the solar system. It is the only planet that has both liquid water and an oxygen-nitrogen atmosphere, two features essential to life as we know it. It is also the only planet known to harbour living creatures. There are over six billion people on Earth now, and countless animals and plants.

As the Earth orbits the Sun it also rotates on its axis. When we’re facing the Sun it’s daytime, and when we’re facing away it’s night. Because the Earth rotates on its axis as it orbits the Sun, parts of the Earth that face the Sun experience daytime while parts that face away experience night. Though the Earth rotates once every 23 hours 56 minutes, the period from one sunrise to the next is actually 24 hours. That’s because the Earth changes position from one day to the next as it moves around the Sun. As a result, it must rotate for an additional 4 minutes to bring the Sun back to the same position in the sky.

Because the Earth rotates on its axis as it orbits the Sun, parts of the Earth that face the Sun experience daytime while parts that face away experience night. Though the Earth rotates once every 23 hours 56 minutes, the period from one sunrise to the next is actually 24 hours. That’s because the Earth changes position from one day to the next as it moves around the Sun. As a result, it must rotate for an additional 4 minutes to bring the Sun back to the same position in the sky.

The basics

Order (outwards from the Sun): 3
Average distance from the Sun: 149 600 000 km (1.00 astronomical unit)
Period of revolution (length of year): 365.25 days
Period of rotation (length of day): 23 hours 56 minutes
Diameter: 12 756 km
Atmosphere: 78% nitrogen, 21% oxygen, traces of carbon dioxide, water vapour.
Satellites: 1 (the Moon), plus numerous man-made satellites
Composition: Basaltic rock continents with an iron core. Liquid water covers about two-thirds of the Earth’s surface
Surface temperature: Range of -89 degrees Celsius to 55 degrees Celsius, depending on season and location.

Appearance of surface

Mostly covered with liquid water. Rocky continents with a wide variety of geologic formations. Green plants cover large areas of the land. Effects of human population (farming, mining, nighttime lighting of cities) visible from orbit.


© Canadian Heritage Information Network 2003

Earth Rotation

Because the Earth rotates on its axis as it orbits the Sun, parts of the Earth that face the Sun experience daytime while parts that face away experience night. Though the Earth rotates once every 23 hours 56 minutes, the period from one sunrise to the next is actually 24 hours. That's because the Earth changes position from one day to the next as it moves around the Sun. As a result, it must rotate for an additional 4 minutes to bring the Sun back to the same position in the sky.

Planétarium de Montréal

© Planétarium de Montréal


The Moon is our closest neighbour in space. It orbits the Earth at an average distance of 384,000 km and takes 27.3 days to complete one revolution. As it orbits the Earth the Moon is illuminated from different angles by the Sun, which produces a quarter lunar phase roughly each week. Since the Moon is only one quarter the Earth’s diameter, it has much less mass and only 1/6th the Earth’s gravity.

Because the Moon takes the same amount of time to rotate on its axis as it does to revolve around the Earth, one side of the Moon always faces us. Long ago, the Moon used to rotate more quickly but the earth’s gravity gradually slowed it down.

Scientists believe the Moon formed 4.6 billion years ago when a Mars-sized asteroid tore a huge chunk out of the Earth. This chunk later solidified in orbit around the Earth and became the Moon. Lunar samples, gathered by the Apollo astronauts, show that the Moon consists of exactly the same minerals as parts of the Earth.
The Moon is our closest neighbour in space. It orbits the Earth at an average distance of 384,000 km and takes 27.3 days to complete one revolution. As it orbits the Earth the Moon is illuminated from different angles by the Sun, which produces a quarter lunar phase roughly each week. Since the Moon is only one quarter the Earth’s diameter, it has much less mass and only 1/6th the Earth’s gravity.

Because the Moon takes the same amount of time to rotate on its axis as it does to revolve around the Earth, one side of the Moon always faces us. Long ago, the Moon used to rotate more quickly but the earth’s gravity gradually slowed it down.

Scientists believe the Moon formed 4.6 billion years ago when a Mars-sized asteroid tore a huge chunk out of the Earth. This chunk later solidified in orbit around the Earth and became the Moon. Lunar samples, gathered by the Apollo astronauts, show that the Moon consists of exactly the same minerals as parts of the Earth.

© Canadian Heritage Information Network, 2003

In August 1996, scientists announced the discovery of a 1.9 kg (4.2 Ib) rock, determined to have originated on Mars and showing evidence of what appears to be the fossil remains of microscopic bacteria that lived on Mars 3.6 billion years ago. If confirmed, this discovery will be one of the most significant in astronomy.

The Mars Global Surveyor camera has sent back photos showing recent flow patterns, areas which look like dry riverbeds, that may have been caused by water.

The basics 

Order (outwards from the Sun) : 4
Average distance from the Sun : 227 900 000 km (1.524 astronomical units)
Period of revolution (length of year) : 686.95 days
Period of rotation (length of day) : 24 hours 37 minutes
Diameter : 6 794 km
Surface gravity : 0.38 times greater than Earth’s
Atmosphere : Thin carbon dioxide
Satellites : 2 small moons (Phobos and Deimos)
Composition : Basaltic rock
Surface temperature : As low as -140 degrees Celsius, but occasionally as high as 27 degrees Celsius

Appearance of surface

Cold desert world covered with r Read More

In August 1996, scientists announced the discovery of a 1.9 kg (4.2 Ib) rock, determined to have originated on Mars and showing evidence of what appears to be the fossil remains of microscopic bacteria that lived on Mars 3.6 billion years ago. If confirmed, this discovery will be one of the most significant in astronomy.

The Mars Global Surveyor camera has sent back photos showing recent flow patterns, areas which look like dry riverbeds, that may have been caused by water.

The basics 

Order (outwards from the Sun) : 4
Average distance from the Sun : 227 900 000 km (1.524 astronomical units)
Period of revolution (length of year) : 686.95 days
Period of rotation (length of day) : 24 hours 37 minutes
Diameter : 6 794 km
Surface gravity : 0.38 times greater than Earth’s
Atmosphere : Thin carbon dioxide
Satellites : 2 small moons (Phobos and Deimos)
Composition : Basaltic rock
Surface temperature : As low as -140 degrees Celsius, but occasionally as high as 27 degrees Celsius

Appearance of surface

Cold desert world covered with rocky, dusty terrain. Ice caps of frozen carbon dioxide at the north and south poles. Craters, valleys and dormant volcanoes, much larger than those found on Earth, dot the surface.

Appearance in Earth’s sky

Mars changes its appearance dramatically over the course of its year. At its closest approach to Earth it can be brighter than any of the stars, and quite obviously reddish-coloured. When farthest away, it is a dim red point in the sky.

Telescopic appearance

Mars is the only planet whose surface is easily visible from Earth.

Mars is the only planet whose surface is easily visible from Earth. When Mars is at its closest point to Earth (every two years or so), a telescope can show a reddish disk, as well as the white polar ice caps and some of the dark surface markings. At other times, Mars appears so small that little detail can be seen even with a large telescope.


© Canadian Heritage Information Network, 2003

Mars

Mars changes its appearance dramatically over the course of its year. At its closest approach to Earth it can be brighter than any of the stars, and quite obviously reddish-coloured.

NASA and the Hubble Heritage Team (STScI/AURA)

© NASA and the Hubble Heritage Team (STScI/AURA).


Learning Objectives

The learner will:

  • Understand the concept of planet and moon
  • Describe the basic features of Mercury, Venus, Earth and the Moon, and Mars
  • Describe how the Moon was formed

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