Stellar drift
Encyclopedia
Stellar drift, or the motion of stars, is a necessary result of the lack of an absolute reference frame in special relativity. The term is used mainly in science fiction, however; in particular, the phenomenon affects stargates
in the Stargate
franchise.
Nothing in space stands still—more precisely, standing still is meaningless without defining what "still" means. Most galaxies
have been moving away ever since the Big Bang
, as explained by the metric expansion of space
. Galaxy motion is also influenced by galaxy groups and clusters
. Stars orbit moving galaxies, and they also orbit moving star cluster
s and companion star
s. Planets orbit their moving stars.
Stellar drift is measured by two components: proper motion
(multiplied by distance) and radial velocity
. Proper motion is a star's motion across the sky, slowly changing the shapes of constellation
s over thousands of years. It can be measured using a telescope to detect small movements over long periods of time. Radial velocity is how fast a star approaches or recedes from us. It is measured using redshift
. Both components are complicated by the Earth's orbit around the Sun, so the motions of stars are described relative to the Sun, not the Earth (kinematics of stars).
Stargate (device)
A Stargate is a portal device within the Stargate fictional universe that allows practical, rapid travel between two distant locations. The devices first appear in the 1994 Roland Emmerich film Stargate, and thereafter in the television series Stargate SG-1 and its spin-offs...
in the Stargate
Stargate
Stargate is a adventure military science fiction franchise, initially conceived by Roland Emmerich and Dean Devlin. The first film in the franchise was simply titled Stargate. It was originally released on October 28, 1994, by Metro-Goldwyn-Mayer and Carolco, and became a hit, grossing nearly...
franchise.
Nothing in space stands still—more precisely, standing still is meaningless without defining what "still" means. Most galaxies
Galaxy
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 word galaxy is derived from the Greek galaxias , literally "milky", a...
have been moving away ever since the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
, as explained by the metric expansion of space
Metric expansion of space
The metric expansion of space is the increase of distance between distant parts of the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...
. Galaxy motion is also influenced by galaxy groups and clusters
Galaxy groups and clusters
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large scale structure of the universe...
. Stars orbit moving galaxies, and they also orbit moving star cluster
Star cluster
Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...
s and companion star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
s. Planets orbit their moving stars.
Stellar drift is measured by two components: proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
(multiplied by distance) and radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
. Proper motion is a star's motion across the sky, slowly changing the shapes of constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s over thousands of years. It can be measured using a telescope to detect small movements over long periods of time. Radial velocity is how fast a star approaches or recedes from us. It is measured using redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
. Both components are complicated by the Earth's orbit around the Sun, so the motions of stars are described relative to the Sun, not the Earth (kinematics of stars).
See also
- Big BangBig BangThe Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
- Kinematics of stars
- metric expansion of spaceMetric expansion of spaceThe metric expansion of space is the increase of distance between distant parts of the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...