An Etymological Dictionary of Astronomy and Astrophysics
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The forces of jets from a comet's nucleus that can cause a rocket-like effect and alter a comet's direction of motion slightly.

→ non-; → gravitational; → force.

The coupling constant appearing in → Einstein's field equations, expressed by: κ = 8πG/c⁴, where G is the Newtonian → gravitational constant and c the → speed of light.

→ einstein; → gravitational; → constant.

The constant, denoted k, defining the astronomical system of units of length (→ astronomical unit), mass (→ solar mass), and time (→ day), by means of → Kepler's third law. The dimensions of k² are those of Newton's constant of gravitation: L ³M ^-1T ^-2. Its value is: k = 0.01720209895.

→ Gaussian; → gravitational; → constant.

Of or relating to or caused by → gravitation.

Adj. of → gravitation.

The acceleration caused by the force of gravity. At the Earth's surface it is determined by the distance of the object form the center of the Earth: g = GM/R², where G is the → gravitational constant, and M and R are the Earth's mass and radius respectively. It is approximately equal to 9.8 m s^-2. The value varies slightly with latitude and elevation. Also known as the → acceleration of gravity.

→ gravitational; → acceleration.

The force that pulls material bodies toward one another because of → gravitation.

→ gravitational; → attraction.

Collapse of a mass of material as a result of the mutual → gravitational attraction of all its constituents.

→ gravitational; → collapse.

A fundamental constant that appears in → Newton's law of gravitation. It is the force of attraction between two bodies of unit mass separated by unit distance: G = 6.673 x 10^-8 dyn cm² g^-2 or 6.673 x 10^-8 cm³s^-2g^-1, or 6.673 x 10^-11 N m² kg^-2 or 6.673 x 10^-11 m³s^-2kg^-1. It was first measured in 1798 by Henry Cavendish (1731-1810), 71 years after Newton's death. Same as the → Newtonian constant of gravitation.

→ gravitational; → constant.

Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force.

→ gravitational; → contraction.

The dimensionless gravitational constant defined as the gravitational attraction between pair of electrons and normally given by: α_G = (Gm_e²) / (ħc) = (m_e / m_P)² ~ 1.7518 × 10^-45, where ħ is → Planck's reduced constant, c the → speed of light, m_e is the → electron mass, and m_P is the → Planck mass.

→ gravitational; → coupling; → constant.

An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction.

→ gravitational; → encounter.

Same as → gravitational potential energy.

→ gravitational; → energy.

The condition in a celestial body when gravitational forces acting on each point are balanced by some outward pressure, such as radiation pressure or electron degeneracy pressure, so that no vertical motion results.

→ gravitational; → equilibrium.

The region of space in which → gravitational attraction exists.

→ gravitational; → field.

The weakest of the four fundamental forces of nature. Described by → Newton's law of gravitation and subsequently by Einstein's → general relativity.

→ gravitational; → force.

The process by which fluctuations in an infinite medium of size greater than a certain length scale (the Jeans length) grow by self-gravitation.

→ gravitational; → instability.

Mutual attraction between any two bodies that have mass.

→ gravitational; → interaction.

A concentration of matter, such as a galaxy or a cluster of galaxies, that bends light rays from a background object, resulting in production of multiple images. If the two objects and the Earth are perfectly aligned, the light from the distant object appears as a ring from Earth. This is called an Einstein Ring, since its existence was predicted by Einstein in his theory of general relativity.

→ gravitational; → lens.

The main equation of gravitational lens theory that sets a relation between the angular position of the point source and the observable position of its image.

→ gravitational; → lens; → equation.

The act of producing or the state of a → gravitational lens.

→ gravitational; → lensing.