Astronomy and related astronomical terms

(the science of the celestial bodies: the sun, the moon, and the planets; the stars and galaxies; and all of the other objects in the universe)

The astronomer said,
As he raised his cup,
"Thank heavens my business
Is looking up."
—Ennis Rees, Pun Fun;
Scholastic Book Services; New York; 1965; page 13.
An electronic device used to amplify low-intensity light signals by converting them into electrons.

The acceleration of these electrons leads to a cascade, and a relatively large output signal for a small input signal.

Particles that make up electromagnetic radiation.

Photons carry varying amounts of energy and travel at the speed of light.

1. The outermost visible layer, or surface, of the sun which emits light and heat.

The layer of the sun that corresponds to the solar surface viewed in white light or the region from which light escapes from the sun into space.

2. The intensely bright gaseous outer layer of a star, especially the sun.

The photosphere is often marked by large, dark patches called "sunspots" and faculae. The faculae are groups of small shining spots on the surface of the sun which are brighter than the other parts of the photosphere.

About 300 kilometers or 200 miles deep, the photosphere consist of incandescent gas at a temperature of 5,800 Kelvin (5,530° Celsius or 9,980° Fahrenheit).

Kelvin is the basic unit of thermodynamic temperature adopted under the Systeme International d'Unites.

Rising cells of hot gas produce a mottling of the photosphere known as granulation, each granule being about 1,000 kilometers or 620 miles in diameter.

photovoltaic (PV) solar cells
Made of semi-conducting materials that can directly convert sunlight to electricity without any harmful waste product.

Solar collector 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.

It 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 area of illumination on a display or a detection instrument also known as a "picture element" or a "cell".
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. Its own gravity pulls a planet into its most stable shape, a slightly flattened sphere.

planetary albedo
The fraction (approximately 30 percent) of incident solar radiation that is reflected by the earth-atmosphere system and returned to space, mostly by scattering from clouds in the atmosphere.
planetary astronomer
Someone who studies planets, moons, and planetary systems, in particular those of the solar system and the processes that form them.

It includes the studies of objects ranging in size from micrometeoroids to gas giants, with the objectives of determining their compositions, dynamics, formations, interrelations, and histories.

planetary astronomy
The investigation of the solar system and planetary systems using both ground and spacecraft-based observations.

It 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.

planetary boundary layer, PBL
The lower part of the earth's atmosphere that is directly influenced by conditions on the surface; such as, evapotranspiration.

Its height is variable and ranges from 100 to 3,000 meters.

planetary conjunction
Planetary conjunction takes place when a planet is closely aligned with another celestial object; such as, the moon, a star, or another planet.
planetary nebula
1. The cloud of expanding gas surrounding a star that has blown off its outer layers, possibly in a nova stage.
2. 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 bodies ranging in size from millimeter-sized particles to kilometer-sized minor planets, that are believed to have formed the planets by accretion.
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.

Star tipping hat.

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.

Also check out the Index of other Scientific and Technological Topics.