There are three planets easily seen with the unaided eye that are farther from the Sun than Earth is. We call such planets "superior" planets. Venus and Mercury are the only inferior planets, meaning they are closer to the Sun than we are. Mars, Jupiter and Saturn can all be bright objects and have been well known for thousands of years.
The red planet
Perhaps the most glamorous planet is Mars. There is not only the possibility that it might once have harbored life, but there is also its starring role in science fiction books and films such as War of the Worlds. In addition, it's a near certainty that humans will one day walk on its surface.
Like all the superior planets, Mars is most prominent around the time of opposition, a term astronomers use to describe the occasions when it appears opposite the Sun in the sky. At opposition, a planet is closest to the Earth, although in the case of Mars the actual distance can vary considerably because the planet's orbit is noticeably elliptical, not circular.
Around the time of opposition Mars is brighter than any star and appears fiery red in color, hence its ancient association with the god of war. Its color is due to the reddish deserts that cover Mars.
Mars comes to opposition roughly every two years and two months. The next occasions are: 2014 April 8, in Virgo and 2016 May 22, in Scorpius.
Although it's not usually difficult to find Mars in the sky, it's so small that it's hard to see its surface features. In a small telescope, in good conditions, you might see one of the polar caps and possibly some surface markings.
Around the time of opposition Mars also seems to do something strange in the sky - it loops backwards against the stars, before resuming its forward motion, as shown in this multiple-exposure photograph taken by Turkish amateur astronomer TunÁ Tezel. Astronomers call this a retrograde loop. The other outer planets also perform such loops, but the loops are much smaller.
Ancient astronomers were puzzled by this behavior, but we now know that it's due to the Earth catching up and overtaking Mars as the two planets orbit the Sun. It's like a car on the inner lane of a racetrack passing another on an outer lane.
Jupiter, the giant planet
Jupiter is the largest of the planets, 11 times the diameter of the Earth. Swathed in bright clouds, it appears cream-colored to the eye. Jupiter comes to opposition about every 13 months, easily outshining the brightest stars. The last opposition was 2012 December 3, in Taurus. The next one is 2014 January 5, in Gemini.
Through binoculars and small telescopes you can see that Jupiter has a slightly squashed outline. This is because the planet spins so quickly on its axis that it bulges at the equator. Dark bands in its clouds can be seen through telescopes, along with a famous feature called the Great Red Spot, a swirling storm cloud larger than the Earth.
Binoculars also reveal Jupiter's four largest moons: Io, Europa, Ganymede and Callisto. These are popularly termed the Galilean moons because they were discovered by Galileo just over 400 years ago. They look like tiny points of light changing position from night to night as they orbit Jupiter, sometimes disappearing behind the planet or crossing in front of it.
Saturn, the planet with the bright rings, is one of the most beautiful sights in the sky. To the unaided eye, it appears as a bright yellowish star. You can just make out the elongated outline of the rings through binoculars, but a telescope is needed to see them properly.
Around opposition, in good conditions, it's possible to see Titan with binoculars. Titan is Saturn's biggest moon. You would see it as a faint point of light fairly close to Saturn.
Distant and slow-moving, Saturn comes to opposition only about two weeks later each year. The next opposition is 2014 May 10, in Libra.
I am including Uranus here as a matter of interest, because it is - in the right conditions - a planet that can be seen with the unaided eye. Besides good conditions, you also need to know where it is. It can appear quite bright in binoculars, but Uranus tends to be a telescopic object.
Even experienced observers consult sky charts and guides in order to find Uranus. This is where finding a local astronomy society is helpful, because someone may be able to show you sights such as Uranus or Neptune when they're visible. But I'm not including Neptune in this article because you do need a telescope to see it.