Planets & Moons
Earthīs companion planets and their moons
10 Amazing Facts about Mercury
Mercury was a mystery planet for a long time. It's so close to the Sun it's only visible around sunrise and sunset, and the Sun's glare wipes out surface detail. Space probes have now studied Mercury, and it turned out to be full of surprises.
10 Amazing Facts about Saturn's Moons
Saturn lies in the outer Solar System, ten times farther away from the Sun than Earth is. It's best known for its fabulous ring system, but it also has an amazing system of moons including ring shepherds and the smallest natural round body in the Solar System.
Absolute Beginners - Seeing Mars and beyond
Three beautiful planets - Mars, Jupiter and Saturn - are all visible to the unaided eye. If you have binoculars or a telescope, you can also see some of the moons and other features. Hereīs a beginnerīs guide to the planets which lie beyond Earth.
Absolute Beginners - Seeing Mercury and Venus
We can see five planets with our unaided eyes. But people often ask how to find them and how to recognize them. Here is a beginnerīs guide for seeing Mercury and Venus.
Astronomers on the Mountain Tops
Big telescopes on high mountains, drawing astronomers to some exotic-sounding places. Is it as glamorous as it sounds? Not really, says one astronomer who describes some of the symptoms people suffer at high altitudes.
Beagle 2 Lost and Found
On Christmas day 2003 a British-European space probe called Beagle 2 was lost on Mars and never heard from. It was not only small, but possibly broken and scattered while attempting to land. Since Mars is quite big, it took eleven years to find the little lander, and there were some surprises.
Ceres Facts for Kids
Bodeīs Law predicted a planet between Mars and Jupiter. The Sky Police were looking for it, but Giuseppe Piazzi found it. Then someone found another one. And another one. We know of hundreds of thousands of asteroids now. Discover Ceres - planet, asteroid and dwarf planet.
Chemical Cosmos - book review
"The Chemical Cosmos: A Guided Tour" is an astronomy book about chemistry - or perhaps a chemistry book about astronomy. Itīs an engrossing guided tour that will take you from the baby Universe through the first stars, the formation of solar systems and to our search for the origins of life.
Cosmic Fatherīs Day
What sort of tie would you give a cosmic father? What would you feed him? Where might he find challenging mountaineering, make an astounding golf shot or get up an interstellar soccer game? How can you send a special man a genuinely galactic greeting? Hereīs how.
Cosmic White Christmas
If youīre dreaming of a white Christmas, the cosmos may have something of interest. How about deep snow on one of Saturnīs moons, a gigantic Christmas tree whose lights are baby stars, a snowman on an asteroid or an Einstein ring?
Earth & Moon
Our home. And our close companion, object of awe, subject of poetry and the only other world on which humans have walked. What do we know about it?
In the darkness of space we see the part of the Moon that the Sun illuminates. But sometimes there is a bright crescent Moon with a dark shadow filling in the rest of the Moonīs face. What lets us see the Moonīs night side, and how might the phenomenon detect life on distant worlds?
Enceladus 10 Amazing Facts
Saturn's moon Enceladus is a strange one. There are eruptions of cold volcanoes. This adds snow to a surface so bright it reflects 99% of the Sun's light, and supplies particles to maintain one of Saturn's rings. And does the moon harbor life in the salty ocean that lies under the ice?
Epsilon Eridani - A Norse God in the River
Eridanus is the great river that flows through the southern sky. One its stars, Epsilon Eridani, is of special interest to us because of its nearness and because the sunlike star has a planetary system. Benefiting from a new IAU naming policy, the star and its planet are now also Ran and AEgir.
Exploring Stars and Planets - book review
Looking for an astronomy book for readers 8-14? Philipīs has a brand new edition of Ian Ridpathīs best seller. Clearly written and illustrated with up-to-date images, itīs the story of the Solar System. But there are also glimpses into galaxies, exploding stars and the history of the Universe.
Galactic Winter Games
Welcome to the Galactic Winter Games, a starry tribute to Earthīs Winter Olympic Games. Itīs a tour of some really cool cosmic sights as well as some hot ones, such as one of the biggest explosions in the Universe.
Millions of people have followed the treks of the Martian rovers Spirit and Opportunity as they explored the red planet. In 2009 Spirit became trapped and was last heard from in March 2010. After a year being unable to contact her, on May 24, 2011, with sadness, NASA formally ended her mission.
How to Tell a Planet from a UFO
Two English policemen chased a UFO through the Devon countryside. It was the planet Venus. A news reporter had quite a scoop when she found a UFO hovering over New York City. It was the planet Jupiter. Why are planets and stars often mistaken for spacecraft or aircraft?
Hyperion Saturn's Weird Wobbly Moon
Saturn has lots of moons more than five dozen of them with confirmed orbits. They are remarkable in many ways, but perhaps the strangest one is the misshapen and unpredictable Hyperion.
Jumbos of the Solar System
Our Solar System is full of wondrous things. Did you know that the mass of Jupiter is two and a half times greater than all the other planets put together? And which is the biggest moon, tallest mountain and biggest ocean? The answers may surprise you.
One planet in the Solar System dominates the others, so it's fitting that it's named for Jupiter, the king of the Roman gods. Jupiter has moons galore and monster storms, and it spins so fast that its day is only ten hours long.
Jupiter Facts for Kids
King of the Roman gods, comet-killer, contains two and a half times the mass of all the other planets put together, has the shortest day of any planet in the Solar System. Itīs Jupiter! Find out more.
Jupiter's Galilean Moons
Four moons circling Jupiter. It was a sensation when Galileo discovered them in the early 17th century and they're still sensational! One is bigger than a planet. Another seethes with volcanic activity and has mountains taller than Everest. And which one has an ocean that could harbor life?
Jupiterīs Moons Facts for Kids
Jupiter has at least 67 moons. Some of them are only half a mile long, but one is bigger than the planet Mercury. Which moon has hundreds of volcanoes, and which one has a deep ocean under an icy surface? Find out here.
Literary Moons of Uranus
Solar System moons are named from mythology. Except for Uranus - its moons are named from English literature, primarily Shakespeare. How did this come about and what is the connection with the moons of Saturn?
Mars Facts for Kids
The red planet has no little green men, but itīs a fascinating place. It has a mountain three times the height of Everest and a deep valley that dwarfs the Grand Canyon. Although Mars has no liquid water on the surface, if the southern polar icecap melted, it could cover the planet 36 feet deep.
Mars Myths Would You Believe Them
Which famous astronomer kept seeing canals on Mars, even when they couldn't be seen with the world's biggest telescope? What was the tragic outcome of a fictional invasion from Mars? Is NASA hiding evidence of an ancient Martian civilization? Does Mars ever look as big as a full Moon?
Mercury Facts for Kids
Now that Pluto is a dwarf planet, Mercury is the baby of the planets. Itīs close enough to the Sun for lead and zinc to melt during the day. Yet there may be frozen water in deep craters. Until space probes came along Mercury was a mystery hidden in the Sunīs glare, but thatīs changing!
Moons of Mars - Deimos
By the late 19th century we knew Jupiter, Saturn, Uranus and Neptune had moons. But it seemed that there were no Martian moons. Then in 1877 American astronomer Asaph Hall surprised the world with two Martian moons. Why did it take so long to find them? And why did Hall call them Fear and Terror?
Moons of Mars - Phobos
Mars has two tiny shapeless moons. The larger moon Phobos zooms around Mars so quickly, that it seems to rise in the west and set in the east twice a day. And it hasn't had easy time of it. Long ago it was nearly shattered by a giant impact. It's now being pulled towards Mars and its destruction.
From ancient times to the present, fifteen Solar System objects have been called planets. But there are only eight planets now. Find out what happened to the other seven and how the planets got their names.
Neptune Facts for Kids
Far beyond Uranus is another blue planet, one named for the Greek sea god. It could well have been named for a god of winds as itīs the windiest place in the Solar System. Here is an update on facts about Neptune, the planet that was discovered using math.
Neptune's Little Moons
Neptune, named for the Roman sea god, is the last planet out from the Sun, lying at the inner boundary of the Kuiper Belt. It has fourteen known moons and they're a mixed bag. One of them - Triton - represents over 99% of the total mass of Neptune moons. Thirteen little moons share what's left.
Planets of the Solar System - Quiz
How well do you know the planets of the Solar System? Here's a beginner's quiz for you to test your knowledge. It's complete with answers and some more facts about the planets.
Rhea - Saturnīs Moon Facts for Kids
Even being Saturnīs second biggest moon doesnīt make Rhea very big. You could fit three Rheas across the USA and still have room left over. It whizzes around Saturn in four and a half days, making for very short months. Itīs so cold there that ice is literally as hard as rock.
Rhea Moon of Saturn
Rhea was Saturn's wife in classical mythology. Rhea the moon zips around Saturn in four and a half days. Although it has an oxygen atmosphere, we won't be moving there anytime soon. Even in direct sunlight, it's -281 degrees Fahrenheit and the "atmosphere" is similar to a vacuum on Earth.
Saint Patrickīs Day Wearing the Cosmic Green
Saint Patrickīs Day is associated with the shamrock and the color green. Although there donīt seem to be any cosmic shamrocks, there are many green phenomena in the skies. Discover a beautiful green nebula, what excites electrons and why con men sold comet pills.
Saturn Facts for Kids
Saturn is golden in the sky and a telescope shows a ring system to take your breath away. If you could find enough water, Saturn would float, and its moons are amazing. But if you donīt like freezing weather, 1000-mph winds and lightning storms the size of continental USA, donīt plan any visits.
Saturnīs Moons Facts for Kids
Everybody recognizes Saturnīs rings, but that isnīt all that orbits the planet. There are shepherd moons, a moon with cold volcanoes erupting, a planet-sized moon, and more. It took nearly two hundred years for the first seven known moons to get names.
The Transit of Venus - book review
In the north of England in the early 17th century, there was an amazing circle of astronomers. They were well ahead of their time and included the first two people ever to observe a transit of Venus. What ended this brief flowering? Peter Aughton tells the story.
Titan Facts for Kids
Saturnīs moon Titan is bigger than a planet. Itīs the only moon with a thick atmosphere. In fact the atmosphere is so smoggy, we canīt see the surface. But the Cassini-Huygens mission has found out many of its secrets, including lakes and sand dunes and maybe volcanoes.
Top Astronomy Stories 2012
What were the big astronomy stories of the year 2012? Here is my choice of the top ten plus a non-story. What do you think?
Top Ten Astronomy Stories 2014
What happened in the skies in 2014? Hereīs my top ten. Some hints: it takes in stories all the way from a tiny lander alone on a comet to a supercluster of galaxies 500 million light years across, perhaps another Earth, and an ocean on one of Saturnīs moons.
Transit of Mercury
No one alive had seen Venus transit when the 2004 one occurred. And if you missed that and the 2012 transit, there isn't another until 2117. However Mercury also transits the Sun and these transits happen more often. But what's a transit and what do we learn from it?
Transit of Venus - Measuring the Solar System
On June 8, 2004 millions of people witnessed an event that no one still alive had ever seen: a transit of Venus. Another one will occur in June 2012 and then not again for over a hundred years. What is a transit of Venus? How did it help in working out the size of the Solar System?
Triton Captive Moon of Neptune
The Solar System's big moons are weird and wonderful, and Triton is no exception. It has ice volcanoes. Its "cantaloupe terrain" is unique in the Solar System. It's unlike the other large moons. And it orbits in the wrong direction, so it didn't form near Neptune. But where did it come from?
Triton Facts for Kids
Neptuneīs big moon Triton was nameless for over a hundred years after its discovery. And it was so far away that astronomers knew almost nothing about it. Then Voyager 2 visited and saw active ice volcanoes on a moon that is probably a cousin to Pluto.
Uranus and Neptune - Twin Planets
Uranus and Neptune are ice giants and twin planets. They are very similar in many ways, but they aren't identical twins. For example, Uranus orbits lying down and Neptune is much warmer than it should be.
Uranus Facts for Kids
This ice giant is twenty times further from the Sun than we are. It orbits lying on its side so that half the planet can be dark for over twenty years at a time. This is the planet Uranus, discovered by William Herschel in 1871 and nearly named George!
Venus Facts for Kids
Itīs the planet most likely to mistaken for a UFO. It spins backwards on its axis. A day is longer than a year. Itīs Venus! Some call it Earthīs twin, but I think youīll see that we donīt have all that much in common.
Volcanoes - Fire and Ice
A volcano can produce a fiery sky with ash and deadly gases. The biggest one on Earth is Mauna Loa, but it's dwarfed by Olympus Mons on Mars which is three times the height of Everest. There are many volcanoes in the Solar System, including ice volcanoes.
Voyager 1 Gas Giants and a Last Look Homeward
When a rare planetary alignment opened up the outer Solar System, Voyager 1 was sent forth. It observed the gas giants Jupiter and Saturn and their moons. At nearly 4 billion miles from the Sun, the probe turned and took one last picture of home before continuing its journey to the stars.
Whatīs in a Name
Things arenīt always what they seem. Many discoveries arenīt named for - or by - their discoverers. Halley didnīt discover Comet Halley. Kuiper said the Kuiper Belt didn-t exist. The Herschels called Uranus "the Georgian planet" after George III of England, but no one else did.
Who Discovered Neptune
Neptune is the planet discovered mathematically and whose detection led to a heated rivalry between British and French astronomers. But who was the first person actually to see Neptune?
Who wants to go to Venus ?
Some people think that Venus could be habitable. And perhaps you might daydream about being closer to the Sun when the long winter nights come, and the temperature drops. After all, "Earth's twin" should be a nice place, shouldn't it? Let's talk about that.
Why Planets Have Seasons Astronomy Homepage | Editor's Picks Articles | Top Ten Articles | Astronomy Site Map
For people living outside the tropics, June 21st is the longest or shortest day of the year, a solstice. It marks the first day of summer in the northern hemisphere and winter in the southern hemisphere. But why do we have seasons? And do other planets have them?
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