There are 5 planets you can see with your own eyes! From Earth, we can see the five closest planets – Mercury, Venus, Mars, Jupiter, and Saturn. To your eyes they appear as stars. They do not create light like a star, rather sunlight illuminates their surfaces and we see them the same way we see our Moon, just not the same size. The Moon appears so large because it is close and the planets appear like dots or ‘stars’ because they are so far away.
The 5 planets were discovered before the invention of the telescope. Ancient people called these five planets ‘wanders’ because they appear to wander against the background of stars. This is due to the orbital movement of the planets. The word ‘planet’ comes from the Greek word ‘wander’.
One good way to tell stars from planets is that looking at them with the unaided eye,
stars twinkle and planets do not. The twinkling of stars, technically known as stellar scintillation, is caused by the Earth's atmosphere. Because stars are so incredibly distant from us, any disturbances in the atmosphere will bounce around the light from a star in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle".
Picture: Image of the Moon & Venus both in a crescent phase (Astronomy Picture of the Day 3/6/09). Just like our Moon, the planet Venus has phases although you need binoculars or a telescope to see the phase.
Mercury
Observing Mercury in 2009
October: Look to the east in the pre-dawn sky for your best morning view of the planet.
November: Too close to the Sun for viewing this month.
December: Look for it in the sunset sky.
What to look for: Mercury is the closest planet to the Sun making it the most challenging planet to observe. It is only visible during twilight - just before sunrise or just after sunset. The window for observing Mercury is measured in minutes. The best times to view the planet is when it is furthest from the Sun in the sky called greatest elongation. When Mercury is at greatest elongation it is visible for about an hour before sunrise or after sunset. Binoculars and telescopes are recommended for viewing Mercury. Because it is an inferior planet (between Earth and the Sun) it has a cycle of phases similar to what we see on the Moon.
Picture: Image of Mercury taken on October 6, 2008 with NASA's MESSENGER (space probe) on its second flyby of the planet.
Venus
Observing Venus in 2009
October: The fading morning star begins to slide back towards the Sun at last.
November: Fading and approaching the Sun, Venus will soon be lost from our pre-dawn sky.
December: Too close to the Sun for safe viewing.
What to look for: Venus is the brightest planet. In fact, it is the 3rd brightest object in our sky (after the Sun and Moon). Venus is often referred to as the 'Morning or Evening Star' as it is only visible during twilight - before sunrise or after sunset. Even thought it appears as a star to your unaided eye, it is a planet and the light is coming from the Sun. Because it is an inferior planet (between Earth and the Sun) it has a cycle of phases similar to what we see on the Moon. Binoculars or a telescope is needed to view the phases.
Morning or Evening: Venus is visible before sunrise (morning) in the months of Apr. through Dec. 2009.
Picture: Image of the Transit of Venus on June 8, 2004 (picture from the Astronomy Picture of the Day 6/8/2004). A transit is when a planet (only Mercury or Venus) passes across the face of the Sun as seen from Earth. Only 13 Mercury transits occur in a century and transits of Venus are even rarer (the last one was in 1882). This event is truly a 'once in a lifetime' opportunity...but the event comes in pairs. The next event will be on June 6, 2012 so don't miss it because the next pair of Venus transits will be in the years 2117 and 2125.
Mars
Observing Mars in 2009
October: Brightening dramatically this month, continue to watch for it in the early morning sky.
November: Now in Cancer, Mars continues to improve in brightness.
December: Bright and bold before the sunrise.
What to look for: Mars is known as the 'Red Planet' because it's surface is colored by iron oxide. It appears as an orange-red star in the sky to your unaided eyes, but it is not a star. It is a planet. Sunlight shines on Mars and the distance between us on Earth and Mars makes Mars appear small like a star. The brightness of the planet varies depending where Mars is compared to Earth. When we are close to the Red Planet, it appears brighter than when Mars is on the opposite side of the solar system. When Mars is closest to Earth it does NOT appear significantly bigger to your unaided eyes, just brighter.
Constellation: As planets orbit the Sun, they appear to travel eastward against the background of stars. Mars appears in the constellations Gemini (Sept. & Oct), Cancer (Nov.), and Leo (Dec.).
Picture: Image of Mars on August 27, 2003 taken with the Hubble Space Telescope. On this date Mars was at its closest approach to Earth in almost 60,000 years.
Jupiter
Observing Jupiter in 2009
October: Now setting near midnight, look for it in the south around sunset.
November: Shines beautifully in south at sunset.
December: Still well-visible in the south near sunset.
What to look for: Jupiter is the biggest planet in the solar system, but not the brightest in the sky (Venus takes that title). It is still very bright and hard to miss. Jupiter is a favorite among amateur astronomers because it is always putting on a show. Even with the smallest optical aid such as binoculars, you can see the four largest moons called the Galilean Moons.
Constellation: Jupiter is located in the constellation Capricornus in 2009 (except for the month of January when it is located in Sagittarius).
Picture: Image of Jupiter taken on April 9, 2007 with the Hubble Space Telescope. Jupiter's largest moon, Ganymede, can be seen just before it disappears behind the giant planet.
Saturn
Observing Saturn in 2009
October: Now a morning planet, look for it to rise just before the Sun in the east.
November: Rises before the Sun in eastern sky.
December: Rises in the east near midnight.
What to look for: Saturn is the most distant of the five planets and most famous for its ring system. Galileo thought that Saturn looked like it had fuzzy ears when he observed the planet through his primitive telescope nearly 400 years ago. With your unaided eyes, you cannot see these rings. To your eyes Saturn will appear as a yellowish color.
Constellation: Saturn is located in the constellation Leo from Jan. to Sept. when it moves into the constellation Virgo for Oct. through Dec.
Picture: Image of Saturn taken on February 24, 2009 with the Hubble Space Telescope. In the image, Saturn's largest moon (Titan - larger than the planet Mercury - orange in color) casts a shadow onto Saturn.