ASTR 103 - Astronomy

Glossary - T

tail (of a comet)

 

tangential velocity

Component of the star's motion that is at right angles to the line of sight. Also known as transverse velocity.

telescope

 

temperature (Celsius)

 

temperature (color)

 

temperature (effective)

 

temperature (Fahrenheit)

 

temperature (Kelvin)

 

temperature (kinetic)

 

terrestrial planet

Mercury, Venus, Earth, or Mars.

thermal energy

 

thermal equilibrium

balancing between incoming and outgoing radiation that keeps the internal temperature of the star constant at any point.

thermal radiation

radiation produced by a body because it is hotter than its surroundings. In producing radiation, the body reduces its thermal energy.

thermonuclear fusion

nuclear reaction in which light atoms are coalesced into heavier atoms with the release of energy.

thermosphere

atmospheric layer extending from about 100 to 400 kilometers. It is characterized by a constantly rising gas-kinetic temperature with height.

tidal force

unequal gravitational pull exerted on parts of a body, tending to deform its shape.

time-dependent cosmological model

any nonstatic model in which the Universe evolves (contracts or expands) with time.

time dilation

stretching or slowing down of time seen by an observer with respect to an object moving at high speed in a frame of reference different from that of the observer.

total eclipse

 

transit

apparent passage of a celestial body across the face of another larger celestial body, such as the passage of Mercury across the face of the Sun.

Trojan asteroid

 

tropical year

 

troposphere

bottom layer of Earth's atmosphere, in which our weather takes place. Its height averages about 11 kilometers.

T Tauri variable

low-temperature dwarf star with bright emission lines subject to erratic changes in light. It is found in the vicinity of dark nebulosity and is believed to be the forerunner of a main sequence star.

turbulence

 

turnoff point

critical departure position where an evolving star turns off the main sequence after exhausting its core supply of hydrogen and is on the way to becoming a red giant.

21-cm radiation

radiation at 1420 megahertz emitted by neutral hydrogen when the bound electron reverses its spin from that which was in the same direction as the proton.

twinkling

random light fluctuations observed when radiation from an apparently very small light source passes through a disturbed gaseous medium.