Astronomy and related astronomical terms

Made of semi-conducting materials that can directly convert sunlight to electricity without any harmful waste products: Solar collectors, consisting of photovoltaic solar cells, are made more efficient by using arrays of mirrors to concentrate the sun's ray onto photovoltaic panels.

According to the Department of Energy, homes incorporating solar heating designs can save as much as 50 percent on heating bills.

The negative aspects of solar energy is that it depends heavily on a range of factors including location, time of year, and the weather.

An extensive list of related words and definitions may be seen at this photovoltaic terms page.

An inconspicuous zodiac constellation, mainly in the northern hemisphere between Aries and Aquarius, near Pegasus: Pisces is represented as two fish tied together by their tails. The Circlet, a delicate ring of stars, marks the head of the western fish in Pisces.

The constellation contains the vernal equinox, the point at which the Sun's path around the sky (the ecliptic) crosses the celestial equator.

The Sun reaches this point about March 21 each year as it passes through Pisces from mid-March to late April.

The basic unit of an area of illumination on a screen display: Pixels that appear on a detection instrument are also known as a "picture element" or a "cell".

Large celestial bodies in orbit around a star, composed of rock, metal, or gas: The nine planets in the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

The inner four, called the "terrestrial planets" are small and rocky, and include the planet Earth.

The outer planets, with the exception of Pluto, are called the major planets, and consist of large balls of rock, liquid, and gas. The largest is Jupiter, which contains a mass equivalent to 70% of all the other planets combined.

Planets do not produce light, but reflect the light of their parent star.

The planets are illustrated at the sight indicated below and links are available for more details about their Greek and Latin myths, symbolisms (system of symbols), and scientific information.

Click on this link for significant images and more detailed information about planets.

A rotating body of substantial size held in orbit by the gravitational attraction of a star: A planet is not self-luminous. It reflects starlight.

A planet's own gravity pulls itself into its most stable shape, a slightly flattened sphere.

The fraction (approximately 30 percent) of incident solar radiation that is reflected by the Earth-atmosphere system: Planetary albedos are returned to space, mostly by scattering from clouds in the atmosphere.

Someone who studies planets, moons, and planetary systems, in particular those of the solar system and the processes that form them: A planetary astronomer studies objects ranging in size from micrometeoroids to gas giants, with the objectives of determining their compositions, dynamics, formations, interrelations, and histories.

The investigation of the solar system and planetary systems using both ground and spacecraft-based observations: Planetary astronomy includes the study of Kuiper belt objects, dwarf planets, Titan, other icy satellites, extra-solar planetary systems (from brown dwarfs to stellar disks), and the occasional inner solar system body.

The lower part of the earth's atmosphere that is directly influenced by conditions on the surface, such as evapotranspiration: The height of the planetary boundary layer is variable and ranges from 100 to 3,000 meters.

The situation when two or more planets look as if they are very close together, but in reality they are far apart from each other: A planetary conjunction takes place when a planet is closely aligned with another celestial object, such as the moon, a star, or another planet.

The cloud of expanding gas surrounding a star that has blown off its outer layers, possibly in a nova stage: A planetary nebula is a shell of gas thrown off by a star at the end of its life.

Planetary nebulae have nothing to do with planets. They were named by William Herschel, who thought their rounded shape resembled the disk of a planet.

After a star, such as the Sun, has expanded to become a red giant, its outer layers are ejected into space to form a planetary nebula, leaving the core as a white dwarf at the center.

The general term for one of the numerous celestial bodies ranging in size from millimeter-sized particles to kilometer-sized minor planets: The planetesimals are believed to have formed the planets by accretion.

A two-dimensional representation of the night sky as it would appear to a specific observer at one particular latitude and time: A planisphere is a projection of the entire or part of a sphere on a level surface, like a projection of the polar region of the celestial sphere onto a graph or map.

A planisphere can be described as the modern equivalent of the astrolabe, but more convenient to use.

A gas consisting of electrons and ions: Plasma is called "the fourth state of matter" because the temperature is too high for whole atoms to exist.

The so-called "fourth state of matter" consists of ions and electrons in equilibrium.

Such a state can be arrived at in regions of very high temperatures; such as, those which exist within stars.

An open star cluster about 400 light-years away from Earth in the constellation Taurus, represented as the Seven Sisters of Greek mythology.

The brightest stars of Pleiades (highly luminous, blue-white giants only a few million years old) are visible without the need of a telescope, but there are many fainter ones.