By Elena Athanasiou

The inner planets of the solar system are the four planets of Mercury, Venus, Earth, and Mars.

Mercury

The closest inner planet to the Sun, Mercury is 48 million miles away from the Earth at its closest point in orbit. It is a mere 28.6 million miles away from the Sun at its closest point in orbit. Mercury orbits the Sun every 88 days and rotates around its axis every 58.65 days. Temperatures can range from -300 degrees Fahrenheit to 800 degrees Fahrenheit. Closely resembling the moon, the surface of Mercury is marked by craters from billions of years of cosmic collisions.

Venus

Similar in size to Earth, and therefore called Earth’s “Sister Planet,” Venus is 25 million (40,233,600 kilometers) miles away from the Earth. Its orbit is the most circular of all the planets; it is 67 million miles from the Sun at its closest point and 68 million miles away from the Sun when it’s at its farthest point, a “mere” 1 million mile difference. Venus takes about 243 Earth days to make one rotation about it’s axis. The amount of time it takes to revolve around the Sun is less than that: about 226.3 days. This means daytime in Venus lasts for about 115 days, allowing temperatures to rise. Temperatures on the inner planet of Venus average about 867 degrees Fahrenheit. The surface of Venus is blocked by a dense atmosphere consisting of Carbon monoxide. Clouds of sulfuric acid are highly reflective, making Venus the brightest object in the night sky, save for the Moon.

Earth

Our home planet, Earth, is the largest of the inner planets. It ranges from between 91 and 94.5 million miles away from the Sun during its orbit. Temperatures range from -128 degrees Fahrenheit to 136 degrees Fahrenheit. From space, the Earth looks blue and white. The surface of the Earth is marked by large oceans and smaller land segments called tectonic plates.

Mars

Mars is about 35 million miles away from the Earth and ranges from 128 million miles and 155 million miles away from the Sun. Its day is similar to that of the Earth at about 24.6 hours and takes the equivalent of 1.88 Earth years to orbit the Sun. Also known as the “Red Planet” due to the layer of iron oxide covering the planet, Mars also marked by a number of craters. However the atmosphere of Mars is enough to prevent the sort of impacts that we see marking the Moon’s surface. This atmosphere is very thin and subjects Mars to the harsh solar winds.

I hope you enjoyed discovering some of the basic facts and figures about the inner planets. Our solar system is a vast, expansive place, full of mystery and wonder. There is so much more to learn about the inner planets, our solar system, and the universe; click on the links below to learn more!

The outer planets of our Solar System, upon examination, help us to really understand the sheer size of not only our own system, but the whole Universe. There are four outer planets in our solar system. They are as follows: Jupiter, Saturn, Uranus, and Neptune.

Jupiter

As we venture out past Mars and the Asteroid Belt, we find the fifth and largest planet in our solar system, Jupiter. The largest planet in our solar system, Jupiter, is so big that over 1,000 Earths could fit inside it. Jupiter comes as close as 365 million miles away from the Earth at its closest point in orbit. That’s more than the distance from Mercury to the Earth, Venus to the Earth, and Mars to the Earth combined! Its distance from the Sun is even more remarkable: 460 million miles at its closest and 508 million miles at its farthest point in orbit. It takes Jupiter 12 Earth years to orbit the Sun and spins on its own axis every 9.8 hours. This means that Jupiter is spinning very quickly about its own axis, just short of 3 times as fast as the Earth spins. Jupiter is considerably colder than the Earth. Readings coming from the cloud tops show that temperatures are about -101 degrees Fahrenheit. Jupiter is marked by vast swirls of clouds and its most well known feature is the Great Red Spot. The Great Red Spot is a vast storm that measures about 24,860 miles across. That’s big enough to contain just shy of three planet Earths! Another important feature of Jupiter is its vast number of satellites, or moons. The current tally is at 63.

Saturn

Saturn is the second largest planet, located about 746 million miles away from our planet Earth. This is almost twice as far away as Jupiter is from the Earth! During its orbit around the Sun, Saturn ranges from 840 million miles to 938 million miles away from the Sun. It takes Saturn almost 30 Earth years to make it around the Sun. Like Jupiter, Saturn is spinning about its axis much faster than the Earth. Saturn takes only 10.67 Earth hours to rotate once about its axis. Cloud top temperature readings reveal temperatures of about -274 degrees Fahrenheit. That’s twice as cold as the record temperatures on Earth! Saturn’s most prominent feature is its rings, which are made mostly of ice and rock particles. Saturn’s ring system actually consists of many smaller rings instead of one large ring. The particles range in size from a couple centimeters to over a kilometer in size. Saturn, like Jupiter, also has a high number of moons, and that number currently holds at 60 moons.

Uranus

Uranus marks the point where we start discussing distances in billions of miles, not millions of miles. Uranus is 1.6 billion miles away from Earth, which is a little less than twice as far away as Saturn is from the Earth. This figure alone can help us once again begin to notice the vast scope of our solar system. Uranus ranges from 1.7 billion and 1.87 billion miles away from the Sun in its orbit. Uranus takes 84 Earth years to make one revolution around the Sun. In the average human lifetime, Uranus will make just one passage around the Sun. How long does a day on Uranus last? It takes Uranus just over 17 hours to revolve once on its axis. Temperatures on Uranus are even colder: -328 degrees Fahrenheit. Uranus boasts 27 known moons and a faint ring system.

Neptune

The last recognized planet in our solar system is Neptune. Neptune is closest to our planet Earth when it is 2.68 billion miles away. Neptune’s closest distance from the Sun is 2.77 billion miles and 2.87 billion miles away its farthest distance. That’s almost 30 times as far away from the Sun as planet Earth! While it seems that the time Uranus takes to orbit the Sun is extremely long, Neptune takes almost twice as long. It takes 165 Earth years for Neptune to make a single journey around the Sun. A day on Neptune also takes 17 hours. Temperatures at the cloud tops are just a slight bit colder than the temperatures on Uranus: -346 degrees Fahrenheit. Neptune has 13 known moons and a faint ring system. The most prominent feature of Neptune has to be the beautiful blue color that the methane in the clouds reflects back to the viewer. Neptune also possesses a great storm like Jupiter and is called the Great Dark Spot.

Conclusion

By Elena Athanasiou

As you can see, the farther we journey outward in our solar system, we can begin to see just how expansive the universe is. Our solar system orbits just one star, of billions stars in our galaxy, which is just one galaxy out of billions of other galaxies. Learning about our outer planets is just the beginning of a multitude of areas to discover about the Universe.

Wondering why Pluto isn’t on this list? Check out this article to answer all your questions about why Pluto isn’t a planet anymore.

For more information on the universe, visit NASA.gov.

Please visit my bio page to check out more interesting articles on Astronomy.

Andy Fleming is the author of the astronomy blog AstronomyQuest at [http://astronomyquest.blogspot.com/].

The main aim of AstronomyQuest is to provide an educational resource for the public in new developments and discoveries in astronomy and cosmology. In addition, it contains tips on amateur observing and explanations of various astronomical phenomena, and scientific theories pertaining to astronomy.

The blog also features reviews of media including books, podcasts, DVD’s and websites relating to astronomy.

All content is cast at a level requiring little previous knowledge of either astronomy or mathematics. We also endeavor to be not too Northern Hemisphere-centric!

By J Lindgren

Galaxies are multifaceted in that they often encompass many different kinds of outer space matter, such as star systems, dust particles, and gases. Each individual galaxy is filled with millions and trillions of bright, beautiful stars, and on each galaxy, these stars have their own distinct path, or orbit, to follow. When speaking of how large or small galaxies are, they are measured in light years, rather than acres or miles, and the average galaxy is often millions of light years across, most even larger.

Many scientists and astronomers have debated the existence of what is known as dark matter for years, and still have been able to reach a definitive conclusion as to whether it does actually exist or not. They do agree in believing that most space galaxies are gilled with massive balk holes and other unknown rarities yet to be discovered. There are literally billions of different galaxies all floating around in space, and probably billions more that we do not know about, or do not have the technology to see yet. When you think about that, about how big galaxies are, and about how many there actually are in existence, can you imagine how big the whole of outer space must be? It blows your mind just to think about it.

When you talk to someone about galaxies, most of us often name the Milky Way, as it is the galaxy that we are the most familiar with. On clear nights, you can actually see the Milky Way galaxy when looking up at the night sky. We know that the Milky Way galaxy is extremely massive in size, and is made up of trillions and trillions of stars. One shocking fact about the Milky Way, to me anyway, is that when compared to the sun, it is literally huge. We consider the sun to be enormous, but if you were to place the sun and the Milky Way side by side for comparison, you would have to use a microscope to see the sun, if that helps you get a better mental image of just how massive the Milky Way is.

To help them keep better track of all of the galaxies existing in the universe, astronomers and scientists have classified them into three different groups. One of these three groups has been dubbed the spiral, given its name due to all of the galaxies in it being in a spiral shape. The stars surrounding the galaxies in the spiral group do not move around them in a certain path, as in many other galaxies, they instead gravitate in and out through the spirals.

Galaxies belonging to the field group are those galaxies that seem to float freely through space, alone in a huge world, not really touching or near other galaxies. There are not very many galaxies in this group, and perhaps it is the smallest of all three groups.

The last group is perhaps the largest of all three, the cluster group. Galaxies within the cluster group are all squeezed into the same teeny space, but travelling together, are massive in size. There are also galaxies that are referred to as super clusters, where there are many galaxies all in one, again packed tightly into the same space.

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