The sun is a star, a hot ball of glowing gases at the heart of our solar system. Its influence extends far beyond the orbits of distant Neptune and Pluto. Without the sun's intense energy and heat, there would be no life on Earth. And though it is special to us, there are billions of stars like our sun scattered across the Milky Way galaxy. If the sun were as tall as a typical front door, the Earth would be the size of a U.S. nickel. The temperature at the sun's core is about 27 million degrees Fahrenheit.

Average diameter: 864,000 miles, about 109 times the size of the Earth.

Rotation period at equator: About 27 days.

Rotation period at poles: About 36 days.

Surface temperature: 10,000 degrees Fahrenheit.

Composition: Hydrogen, helium

The Sun The heart of Our Solar System

Mercury The Wild Child of The Sun

Mercury almost completely lacks an atmosphere, which actually contributes to its extreme physical conditions. As the closest planet to the sun, it's no surprise that the planet can get extremely hot. However, the lack of atmosphere means that it is unable to retain the heat and as a result, it exhibits incredible temperature fluctuations.

In addition to barely having an atmosphere, Mercury doesn't have much in the way of axial tilt. Because of this, there are no seasonal changes in weather. It also rotates incredibly slowly, as it only completes about three “days” every two years. When Mercury is closest to the sun, the surface temperature can reach over 430º C (approx. 800ºC ). During nighttime, temperatures can drop down to -180ºC (-290ºF).

If a human were to visit Mercury, he or she would either burst into flames or freeze solid depending on where the spaceship landed.

Venus The Goddess of Love 

Our neighbor Venus is essentially the poster child for how greenhouse gasses can create a completely hellish environment. With a super-thick atmosphere of mostly carbon dioxide, Venus is able to trap more of the sun’s radiation than Mercury, which allows it to reach (and retain) much higher temperatures. The surface temperature stays relatively consistent all year at 480ºC (900º  F). The pressure on Venus is approximately 90 times higher than sea level on Earth. In order to recreate that pressure here, a diver would need to go 1000 meters underwater.Rain on Venus is almost purely sulfuric acid, which is extremely corrosive. Sulfuric acid can erode clothing nearly instantly and produce severe burns on flesh. However, the surface temperature of Venus is so great, the rain evaporates before hitting the ground. There is a little water in the atmosphere, which can produce violent explosions when it meets the sulfuric acid. Though Venus is only slightly smaller than Earth, it takes only four hours for the atmosphere to completely rotate around the planet. In contrast, it it takes about 243 days to accomplish the same task on Earth. 

Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases not only contains the air that we breathe but also protects us from the blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night.

Earth's atmosphere is about 300 miles (480 kilometers) thick, but most of it is within 10 miles (16 km) the surface. Air pressure decreases with altitude. At sea level, air pressure is about 14.7 pounds per square inch (1 kilogram per square centimeter). At 10,000 feet (3 km), the air pressure is 10 pounds per square inch (0.7 kg per square cm). There is also less oxygen to breathe.

The Earth Our Mother

Mars The Red Planet

Mars is currently under a lot of investigation as some believe it may have harbored life in the past and could give clues to the origin of life on Earth. Because it once was home to flowing water, there must have been an atmosphere capable of holding it there. Now the surface is dry and huge cyclones of dust can tear apart the landscape. 

Mars’ missing atmosphere is a mystery but there is still plenty of bizarre weather happening on the planet. The poles are covered in ice caps and there are intense snowstorms. While our snow is made of frozen water, Martian snow is actually made from frozen carbon dioxide, which we know as “dry ice.”

Like Mercury, Mars’ super-thin atmosphere has a hard time trapping heat from the sun. Temperatures at the equator can be a comfortable 20ºC (70ºF) in the sun, but at night, the same spot can dip to -50ºC (-58ºF).

Massive dust storms can take over Mars quite easily. While dust devils occur in dry areas on Earth, the ones on Mars can envelop the entire planet over the course of a few days. 

As for what it might look like for a human to visit Mars, we might not have to wait too much longer. Some are hoping to send the first astronauts to Mars within the next few decades.

Jupiter The Gaint

It doesn’t take a particularly large telescope to see that Jupiter has a lot of gigantic storms. The most famous of these storms is known as the Great Red Spot (GRS), which has been raging on like a hurricane for at least 400 years. This storm is so massive, three Earths could fit inside it easily. There is another spot known as the Oval BA, which was discovered about seven years ago and is now moving as fast as its larger counterpart. It even appears to be increasing in size!

The stripes on Jupiter are caused by jet streams. Jet streams on Earth vary, though we usually only have 1 or 2 in each hemisphere. Jupiter is home to at least 30 that tear across the planet in opposite directions, reaching speeds of over 482 km/h (300 mph). Two of these jet streams are responsible for holding the GRS in its present location. The clouds that appear as stripes are composed of frozen ammonia, as the temperature at that part of the atmosphere is -140ºC (-220ºF). Earlier this year, it was discovered that Jupiter can form diamonds in its atmosphere

Like Jupiter, Saturn’s atmosphere is composed mostly of hydrogen. Wind speeds can reach as high as 1609 km/h (1000 mph) which is just about as fast as a speeding bullet. The highest wind speed ever recorded on Earth during a hurricane was in 1996, during Tropical Cyclone Cynthia when gusts reached 408 km/h (253 mph). 

At Saturn’s North Pole there is an extremely cool storm going on. It isn’t circular or rounded like most extreme weather systems, but it is actually shaped like a hexagon. The clearest image of this storm can be seen in a composite that was released last month. Each side of the hexagon is 8,600 miles (13,800 km) long, which is very close to the diameter of Earth.

Though the atmosphere is very thin and cold, there is plenty of heat down towards the surface that can generate some extreme storms. In the northern hemisphere, there is a storm which is 10,000 km across. If that were on Earth, it would be like starting in Los Angeles and traveling due east all the way to Beijing, China.

Toward Saturn’s surface the carbon in the air can be pressed into graphite. Yes, Saturn has pencil lead flying around. Even closer to the core, the carbon is pressed into diamonds. If a human were to travel to Saturn, the diamonds would cut through their body like countless little bullets.

If the sun were as tall as a typical front door, Earth would be the size of a nickel and Uranus would be about as big as a baseball.

Uranus orbits our sun, a star. Uranus is the seventh planet from the sun at a distance of about 2.9 billion km (1.8 billion miles) or 19.19 AU.

One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once. Uranus makes a complete orbit around the sun (a year in Uranian time) in about 84 Earth years (30,687 Earth days).

Uranus is an ice giant. Most (80 percent or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water (H2O), methane (CH4). and ammonia (NH3) – above a small rocky core.

Uranus has an atmosphere which is mostly made up of hydrogen (H2) and helium (He), with a small amount of methane (CH4).

Uranus has 27 moons. Uranus' moons are named after characters from the works of William Shakespeare and Alexander Pope.

Uranus has 13 known rings. The inner rings are narrow and dark and the outer rings are brightly colored.

Voyager 2 is the only spacecraft to have visited Uranus.

Uranus cannot support life as we know it.

Fact: Like Venus, Uranus has a retrograde rotation (east to west). Unlike any of the other planets, Uranus rotates on its side, which means it spins horizontally.

Pluto is classified as a dwarf planet and is also a member of a group of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant realm is populated with thousands of miniature icy worlds, which formed early in the history of our solar system. These icy, rocky bodies are called Kuiper Belt objects or transneptunian objects.

Pluto is about two-thirds the diameter of Earth's moon and probably has a rocky core surrounded by a mantle of water ice. More exotic ices like methane and nitrogen frost coat its surface. Owing to its size and lower density, Pluto's mass is about one-sixth that of Earth's moon. Pluto is more massive than Ceres -- the dwarf planet that resides in the asteroid belt between Mars and Jupiter -- by a factor of 14.

Pluto's 248-year-long elliptical orbit can take it as far as 49.3 astronomical units (AU) from the sun. (One AU is the mean distance between Earth and the sun: about 93 million miles or 150 million kilometers.) From 1979 to 1999, Pluto was actually closer to the sun than Neptune, and in 1989, Pluto came to within 29.8 AU of the sun, providing rare opportunities to study this small, cold, distant world.

Nearly 4.5 billion kilometers (2.8 billion miles) from the Sun, Neptune orbits the Sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth. Interestingly, the highly eccentric orbit of the dwarf planet Pluto brings Pluto inside Neptune's orbit for a 20-year period out of every 248 Earth years. Pluto can never crash into Neptune, though, because for every three laps Neptune takes around the Sun, Pluto makes two. This repeating pattern prevents close approaches of the two bodies.

This dramatic view of the crescents of Neptune and Triton was acquired by Voyager 2 approximately 3 days, 6 and one-half hours after its closest approach to Neptune (north is to the right). 

The encounter put the spacecraft on a couse plunging southward at an angle of 48° to the plane of the ecliptic. This direction, combined with the current season of southern summer in the Neptune system, gives this picture its unique geometry. 

The spacecraft was at a distance of 4.86 million km (3 million miles) from Neptune when these images were taken so the smallest detail discernible is approximately 90 km (56 miles). Color was produced using images taken through the narrow-angle camera's clear, orange and green filters. Neptune does not appear as blue from this viewpoint because the forward scattering nature of its atmosphere is more important than its absorption of red light at this high phase angle (134°).

The Kuiper Belt and the Oort Cloud are regions of space. The known icy worlds and comets in both regions are much smaller than Earth's moon.

The Kuiper Belt and the Oort Cloud surround our sun, a star. The Kuiper Belt is a doughnut-shaped ring, extending just beyond the orbit of Neptune from about 30 to 55 AU. The Oort Cloud is a spherical shell, occupying space at a distance between five thousand and 100 thousand AU.

Long-period comets (which take more than 200 years to orbit the sun) come from the Oort Cloud. Short-period comets (which take less than 200 years to orbit the Sun) originate in the Kuiper Belt.

There may be are hundreds of thousands of icy bodies larger than 100 km (62 miles) and an estimated trillion or more comets within the Kuiper Belt. The Oort Cloud may contain more than a trillion icy bodies.

Some dwarf planets within the Kuiper Belt have thin atmospheres that collapse when their orbit carries them farthest from the sun.

The Kuiper Belt and the Oort Cloud are regions of space and therefore do not have moons. However, several dwarf planets within the Kuiper Belt have moons.

The Kuiper Belt and the Oort Cloud are regions of space and therefore do not have rings. No objects within these two regions are known to have rings.

The first mission to the Kuiper Belt is New Horizons. New Horizons will reach Pluto in 2015.

These two regions of space are not capable of supporting life as we know it.

Fact: Both the Kuiper Belt and the Oort Cloud are named for the astronomers who predicted their existence during the 1950s: Gerard Kuiper and Jan Oort.

Uranus is the only giant planet whose equator is nearly at right angles to its orbit. A collision with an Earth-sized object may explain the unique tilt. Nearly a twin in size to Neptune, Uranus has more methane in its mainly hydrogen and helium atmosphere than Jupiter or Saturn. Methane gives Uranus its blue tint.Discovered: March 13, 1781 by William Herschel.

Distance from the Sun: About 1.8 billion miles, about 19 times further than the Earth.

Year: About 84 Earth years.

Voyager 2 flew past Uranus in 1986, giving us our first close view of the planet. It is still functioning today as it flies in deep space, more than 10 billion miles from Earth. Voyager 2 and its companion spacecraft, Voyager 1, are returning data on how the influence of our sun wanes as they get further from it, and on the characteristics of space between the stars.