Free Faster access than browser!

The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. 

## Amplitude

The amplitude of a periodic variable is a measure of its change over a single period (such as time or spatial period).

## Astrometry

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.

## Binary mass function

In astronomy, the binary mass function or simply mass function is a function that constrains the mass of the unseen component (typically a star or exoplanet) in a single-lined spectroscopic binary star or in a planetary system.

## Binary star

A binary star is a star system consisting of two stars orbiting around their common barycenter.

## Blueshift

A blueshift is any decrease in wavelength, with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift.

## Cosmology

Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of") is the study of the origin, evolution, and eventual fate of the universe.

## Doppler effect

The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to observer who is moving relative to the wave source.

## Doppler spectroscopy

Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star.

## Earth's orbit

Earth's orbit is the trajectory along which Earth travels around the Sun.

## Earth's rotation

Earth's rotation is the rotation of Planet Earth around its own axis.

## Electromagnetic spectrum

The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.

## Exoplanet

An exoplanet or extrasolar planet is a planet outside our solar system.

## Galactic Center

The Galactic Center is the rotational center of the Milky Way.

## Mass

Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.

## Orbit

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet.

## Orbit of the Moon

The Moon orbits Earth in the prograde direction and completes one revolution relative to the stars in about 27.322 days (a sidereal month) and one revolution relative to the Sun in about 29.530 days (a synodic month).

## Orbital eccentricity

The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle.

## Orbital elements

Orbital elements are the parameters required to uniquely identify a specific orbit.

## Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

## Peculiar velocity

Peculiar motion or peculiar velocity refers to the velocity of an object relative to a rest frame — usually a frame in which the average velocity of some objects is zero.

## Planet

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

## Polar motion

Polar motion of the Earth is the motion of the Earth's rotational axis relative to its crust.

## Proper motion

Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.

## Redshift

In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

## Relative velocity

The relative velocity \vec_ (also \vec_ or \vec_) is the velocity of an object or observer B in the rest frame of another object or observer A.

## Relativistic aberration

Relativistic aberration is the relativistic version of aberration of light, including relativistic corrections that become significant for observers who move with velocities close to the speed of light.

## Secular variation

The secular variation of a time series is its long-term non-periodic variation (see Decomposition of time series).

## Semi-major and semi-minor axes

In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the widest points of the perimeter.

## Spectral line

A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies.

## Star

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.

## Stellar kinematics

In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.

## The Astrophysical Journal

The Astrophysical Journal, often abbreviated ApJ (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler.

## Theory of relativity

The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.

## Velocity

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.

## Wavelength

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.

## References

Hey! We are on Facebook now! »