Umbra

a region of complete shadow, which is usually applied to eclipses. The area of half or partial shadow is termed the penumbra.

Taken from Dictionary of Science

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The umbra, penumbra and antumbra are the names given to three distinct parts of a shadow, created by any light source. For a point source only the umbra is cast.

These names are usually used when referring to the shadows cast by celestial bodies.

The umbra (Latin for "shadow") is the darkest part of the shadow. From within the umbra, the light source is completely occluded. In astronomy, an observer in the umbra is said to be in the shadows experiencing total eclipse.

Taken from Wikipedia

Radio Astronomy

the recording and study of radio waves given out by many bodies in space including the Sun, stars and QUASARS.

Taken from Dictionary of Science

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Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. It differs from radar astronomy in that the latter utilizes artificial, rather than natural, radio sources. The initial detection of radio waves from an astronomical object (the Milky Way) was made in the 1930s, but subsequent advances (especially post-World War II) have identified a number of different sources of radio emission. These include stars and galaxies as well as entirely new classes of objects, such as Radio Galaxies, Pulsars and Masers. The discovery of the Cosmic Microwave Background Radiation was a particularly significant event. Radio astronomy is conducted using large radio antenna referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The latter has allowed radio sources to be imaged with unprecedented angular resolution.

Taken from Wikipedia

Parabolic Velocity

in astronomy, the velocity a body would need to make a parabola about the centre of attraction (also called ESCAPE VELOCITY).

Taken from Dictionary of Science

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The velocity which an object at a given point would require in order to describe a parabola about the center of attraction. This is also the escape velocity since it is the upper limit of velocity on a closed curve. It is obtained by multiplying the velocity of an object moving in a circular orbit by the square root of 2 (approx. 1.414). For example, if the Earth's mean velocity around the Sun of 29.8 km/sec. (18.5 miles/sec.), in a near circular orbit, were increased to 42 km/sec. (26 miles/sec.), the Earth would move to a parabolic path and escape from the solar system.

Taken from The Internet ENCYCLOPEDIA OF SCIENCE

Galaxy

(plural galaxies) specifically, the name given to the band of stars, numbering one hundred thousand million bodies, which includes the Sun, and is alternatively called the Milky Way. The galaxy has a spiral structure and is approximately one hundred thousand LIGHT YEARS across. In general usage it refers to a collection of stars held together by gravitational forces. They form different shapes including spiral, elliptical and irregular galaxies and range from dwarf galaxies with 100 000 stars to massive galaxies such as the giant elliptical M 87 which has three thousand billion stars.

Taken from Dictionary of Science

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A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (10⁷) stars up to giants with one trillion (10¹²) stars, all orbiting the galaxy's center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.

There are probably more than 100 billion (10¹¹) galaxies in the observable universe. Most galaxies are 1,000 to 100,000^[4] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.

Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.

Taken from Wikipedia

Absolute Zero

the temperature at which the particles that make up matter have no energy at all whether due to heat or motion. It is theoretically given the value of -273.15°Celsius (-459.67° Fahrenheit).

Taken from Dictionary of Science
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Absolute zero is the temperature at which entropy reaches its minimum value. As implied by the laws of thermodynamics, absolute zero cannot be reached by artificial or natural means because this would require a system to be fully removed from the rest of the universe. A system at theoretical absolute zero possesses quantum mechanical zero-point energy. While all molecular motion does not cease at absolute zero, the system does not have enough energy for transference to other systems. It is therefore correct to say that molecular energy is minimal at absolute zero.

By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale and as −273.15° on the Celsius scale. Absolute zero is also precisely equivalent to 0 R on the Rankine scale (same as Kelvin but measured in Fahrenheit intervals) and −459.67° on the Fahrenheit scale. Though it is not theoretically possible to cool any substance to 0 K, scientists have made great advancements in achieving temperatures close to absolute zero, where matter exhibits quantum effects such as superconductivity and superfluidity.

For the kinematics of molecules at absolute zero on a larger scale, which is easier to understand, see kinetic energy.

Taken from Wikipedia

Abscissa

the term given to the horizontal or x-co-ordinate when describing the position of a point on a graph. It is the distance of the point from the vertical or y-axis. For example, a point two units along the x-axis and three units up the y-axis is said to have CARTESIAN CO-ORDINATES (2,3) where the abscissa is 2.

Taken from Dictionary of Science

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In mathematics, abscissa (plural abscissae) refers to the first element of an ordered pair.

It is the first of the two terms (x, y) by which a point is referred to, in a system of fixed rectilinear coordinate (Cartesian coordinate) axes. The abscissa is also known as the "x" coordinate of a point. The second coordinate, or "y" coordinate, is called the ordinate.

Taken from Wikipedia

Factor

one of two or more quantities that produce a given quantity when multiplied together. For example, the factors of the number 8 are 1, 2, 4, 8.

Taken from Dictionary of Science

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Factors are the numbers you multiply together to get another number:

Example: 3 and 4 are factors of 12, because 3x4=12.

Also 2x6=12 so 2 and 6 are also factors of 12, and 1x12=12 so 1 and 12 are factors of 12 as well.

So ALL the possible factors of 12 are 1,2,3,4,6 and 12.

Taken from Math Is Fun?