PLANETS

Lying within the vast expanse of the solar system, there are nine known planets that orbit the colossal star we all know as the sun. A planet is defined as a large non-luminous celestial mass that is generally larger than smaller celestial bodies such as comets or asteroids.
While it is still not known precisely how the planets of our solar system were formed, the currently accepted nine planets that orbit around and are illuminated by the sun include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The primary distinction between a star and a planet is that a star undergoes nuclear reactions on its surface, where a planet does not.
Every known planet in the solar system, with the exception of Earth and Uranus, is named after a historical Roman god. Uranus is named for a Greek god. Earth was not originally considered a planet by ancient people, but as the supposed center of the entire universe. Each of the planets in the solar system also has at least one additional celestial body, known as a moon that orbits around it while it orbits the sun. Mercury and Venus are the only planets with no known moons. Earth has the next fewest with just one moon, while Jupiter has an incredible 63 discovered moons.
Uncover additional information about the planets of the solar system, including planet articles, planet pictures, interactive planet features and more below.

MERCURY
Mercury is often a difficult planet to find, but there are certain short periods each year when it can be found with the naked eye with little effort, either just after sunset or before sunrise.
In 2007, Northern Hemisphere observers will find two periods when Mercury can easily be found. During late May and early June, Mercury can be seen low in the west-northwest soon after sunset. It is magnitude -0.6 on May 21 and has faded to +0.4 by greatest elongation on June 2 and fades rapidly after that. Throughout November, Mercury is well placed in the east-southeast before sunrise.
Southern Hemisphere observers will find Mercury well placed in the morning sky during late March and early April and will rise well before twilight begins. In late September and early October, Mercury is well placed during the evening after sunset for southern observers.

VENUS
Except for a short period around inferior conjunction in mid August, Venus will be visible throughout the year for both northern and southern hemisphere observers. From January to early August, Venus dominates the evening sky. From late August until the end of the year, Venus is in the morning sky. Even near inferior conjunction, observers in the southern hemisphere may see the thin crescent of Venus low in the sky just before or after sunset. The planet can be seen in the daytime sky with the naked eye if one knows where to look for it, especially around the times of greatest brilliancy and greatest elongation. Try following the planet before sunrise when it is in the morning sky and keep an eye on it until after sunrise.

MARS
Mars is best visible in the morning sky until December and is generally not well placed for observation this year. The opposition on December 24 is not a favorable one but the high declination makes this best for observers in the northern hemisphere. The angular diameter at that time will be 15.9 seconds of arc. There will be an occultation of Mars by the full moon on December 24 visible from NW Canada, Alaska, N Russia, Eastern Europe and NE British Isles.

JUPITER
Jupiter in best viewed in the morning sky until the June 5 opposition, when it moves into the evening sky. It becomes invisible late in the year near conjunction. The angular diameter at opposition will be 45.8 seconds of arc. Jupiter passes highest in the sky for southern hemisphere observers. Binoculars will show the four largest satellites. A small telescope will show two of the cloud bands across the visible surface of the planet.

SATURN
Saturn can be viewed in the evening sky until July, when it approaches conjunction with the Sun. From September to the end of the year, it will be visible in the morning sky. Saturn passes highest in the sky for northern hemisphere observers this year. The ring system will vary in tilt between 7 and 15 degrees this year. The maximum possible tilt is 27 degrees, which last occurred in 2003. The rings will appear edge-on in 2009. At opposition, the angular diameter will be 16.3 seconds of arc. A small telescope will show the rings.

URANUS
Uranus is best viewed in late summer and is in opposition on September 7, when it moves from the morning sky into the evening sky. Although it may be seen with the naked eye in a very dark sky, usually binoculars will be required to make it out. The angular diameter is less than 4 seconds of arc.

NEPTUNE
Neptune is best viewed during the summer and is in opposition on August 13 when it moves from the morning sky into the evening sky. Binoculars or a small telescope will be required to see it. The angular diameter is about 2 seconds of arc.