All of the planets, comets, and asteroids in the solar system are in orbit around the Sun. All of those orbits line up with each other making a semi-flat disk called the orbital plane. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. Three non-collinear points in space suffice to define the orbital plane. A common example would be: the center of the heavier object, the center of the orbiting object and the center of the orbiting object at some later time.

By definition the inclination of a planet in the solar system is the angle between its orbital plane and the orbital plane of the Earth (the ecliptic). In other cases, for instance a moon orbiting another planet, it is convenient to define the inclination of the moon's orbit as the angle between its orbital plane and the planet's equator.

Artificial satellites around the Earth

For launch vehicles and artificial satellites, the orbital plane is a defining parameter of an orbit; as in general, it will take a very large amount of propellant to change the orbital plane of an object. Other parameters, such as the orbital period, the eccentricity of the orbit and the phase of the orbit are more easily changed by propulsion systems.

Orbital planes of satellites are perturbed by the non-spherical nature of the Earth's gravity, and this causes the orbital plane to slowly rotate around the Earth, depending on the angle of the plane. For planes that are at a critical angle this can mean that the plane will track the Sun around the Earth, forming a Sun-synchronous orbit.

A launch vehicle's launch window is usually determined by the times when the target orbital plane intersects the launch site.

A table cell is one grouping within a table. Cells are grouped horizontally (rows of cells) and vertically (columns of cells). Usually information on the top header of a table and side header will "meet" in the middle at a particular cell with information regarding the two headers it is collinear with.

HTML Usage

Kinds of cells in HTML

A table cell in HTML is a non-empty element and should always be closed. There are two different kinds of table cells in HTML: normal table cells and header cells. <td> denotes a table cell, while <th> denotes a table header. The two can be used interchangeably, but it is recommended that header cells be only used for the top and side headers of a table.

Syntax

A table cell also must be nested within a <table> tag and a <tr> (table row) tag. If there are more table cell tags in any given row than in any other, the particular <tr> must be given a colspancell declaring how many columns of cells wide it should be.

Example

An example of an HTML table containing 4 cells:

Colspan and Rowspan

Every row must have the same number of table data cells, occasionally table data cells have to span more than one column or row. In this case the tags colspan and/or rowspan are used - where they are set to a number.