Process

Earth's Water Cycle

Water is always on the move. Rain falling where you live may have been water in the ocean just days before. And the water you see in a river or stream may have been snow on a high mountaintop.

Water can be in the atmosphere, on the land, in the ocean, and even underground. It is recycled over and over through the water cycle.  In the cycle,water changes state between liquid, solid (ice), and gas (water vapor).

Most water vapor gets into theatmosphere by a process calledevaporation. This process turns the water that is at the top of the ocean, rivers, and lakes into water vapor in the atmosphere  using energy from the Sun. Water vapor can also form from snow and ice through the process of sublimation and can evaporate from plants by a process called transpiration.

The water vapor rises in the atmosphereand cools, forming tiny water droplets by a process called condensation.  Those water droplets make up clouds. If those tiny water droplets combine with each other they grow larger and eventually become too heavy to stay in the air. Then they fall to the ground as rain,snow, and other types of precipitation.

Most of the precipitation that falls becomes a part of the ocean or part ofrivers, lakes, and streams that eventually lead to the ocean. Some of the snow and ice that falls as precipitation stays at the Earth surface in glaciers and other types of ice. Some of the precipitation seeps into the ground and becomes a part of the groundwater.

Water stays in certain places longer than others. A drop of water may spend over 3,000 years in the ocean before moving on to another part of the water cycle while a drop of water spends an average of just eight days in the atmosphere before falling back to Earth.

check this link
http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/index.html












source:
http://www.windows2universe.org/earth/Water/water_cycle.html

Classification

Classification of the Major Planets

The major planets are classified either as inferior, with an orbit between the sun and the orbit of Earth (Mercury and Venus), or as superior, with an orbit beyond that of Earth (Mars, Jupiter, Saturn, and Uranus, Neptune. Pluto, long regarded after its discovery in 1930 as the ninth planet, was gradually recognized as a Kuiper belt, or transneptunian, object (see comet), and in 2006 was reclassified by astronomers as a dwarf planet. Any dwarf planet beyond the orbit of Neptune is now classified as a plutoid.

On the basis of their physical properties the planets are further classified as terrestrial or Jovian. The terrestrial planets—Mercury, Venus, Earth, and Mars—resemble Earth in size, chemical composition, and density. Their periods of rotation range from about 24 hr for Mars to 249 days for Venus. The Jovian planets—Jupiter, Saturn, Uranus, and Neptune—are much larger in size and have thick, gaseous atmospheres and low densities. Their periods of rotation range from about 10 hr for Jupiter to 15 hr for Neptune. This rapid rotation results in polar flattening of 2% to 10%, giving the planets an elliptical appearance.

An artist's image shows Pluto (center) and its large "moon" Charon (right) from the surface of one of Pluto's two smaller satellites. The other small moon can be seen on the far left.

Pluto is no longer a planet, according to a new definition of the term voted on by astronomers, because it does not dominate the neighborhood around its orbit. Charon is half the size of Pluto and orbits along with it; the eight true planets are all far larger than their moons.

The planets of the modern solar system are grouped into several different and sometimes overlapping classifications, as illustrated in the following figure:

1. The planets inside the orbit of the earth are called the Inferior Planets: Mercury and Venus.
2. The planets outside the orbit of the earth are called the Superior Planets: Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
3. The planets inside the asteroid belt are termed the Inner Planets (or the Terrestrial Planets): Mercury, Venus, Earth, and Mars.
4. The planets outside the asteroid belt are termed the Outer Planets: Jupiter, Saturn, Uranus, Neptune, and Pluto.
5. The planets sharing the gaseous structure of Jupiter are termed the Gas Giant (or Jovian) Planets: Jupiter, Saturn, Uranus, and Neptune.

Source:
 http://csep10.phys.utk.edu/astr161/lect/classification/classification.html

  http://www.infoplease.com/ce6/sci/A0860415.html

Definition

What Is a Planet?

Most of us grew up with the conventional definition of a planet as a body that orbits a star, shines by reflecting the star's light and is larger than an asteroid. Although the definition may not have been very precise, it clearly categorized the bodies we knew at the time. In the 1990s, however, a remarkable series of discoveries made it untenable. Beyond the orbit of Neptune, astronomers found hundreds of icy worlds, some quite large, occupying a doughnut-shaped region called the Kuiper belt. Around scores of other stars, they found other planets, many of whose orbits look nothing like those in our solar system. They discovered brown dwarfs, which blur the distinction between planet and star. And they found planetlike objects drifting alone in the darkness of interstellar space.

These findings ignited a debate about what a planet really is and led to the decision last August by the International Astronomical Union (IAU), astronomers' main professional society, to define a planet as an object that orbits a star, is large enough to have settled into a round shape and, crucially, "has cleared the neighborhood around its orbit." Controversially, the new definition removes Pluto from the list of planets. Some astronomers said they would refuse to use it and organized a protest petition.

source: http://www.scientificamerican.com/article.cfm?id=what-is-a-planet

 definition provided: defines a planet

Glossary:

asteroid: An asteroid is a rocky body, carbonaceous or metal smaller than a planet larger thana meteoroid, that orbits the Sun in an orbit inside that of Neptune.

Kuiper belt: Region of the solar system with a few thousand rocky objects that are locatedbetween 38 and 200 AU (astronomical units). It is believed that also includes kites,many of which comets are visible at this time. You might think that Pluto may be thelargest Kuiper Belt object.

brown dwarfs: are also called failed stars. They lack enough energy to be true stars but are also too massive and hot to be planets.

blur: A smear, smudge or blot; Something that appears hazy or indistinct.

interstellar space: the space between stars

planetlike: Resembling a planet or some aspect of one