Nuclear Timescale - Stellar Astrophysics

Stellar Astrophysics

Hydrogen generally determines a star's nuclear lifetime because it is used as the main source of fuel in a main sequence star. It constitutes much of the star's core and is surrounded by what is known as a helium shell. Hydrogen becomes helium in the nuclear reaction that takes place within stars; when the hydrogen has been exhausted, the star moves on to another phase of its life and begins burning the helium.

where M is the mass of the star, X is the fraction of the star (by mass) that is composed of the fuel, L is the star's luminosity, Q is the energy released per mass of the fuel from nuclear fusion (the chemical equation should be examined to get this value), and F is the fraction of the star where the fuel is burned (F is generally equal to .1 or so). As an example, the Sun's nuclear time scale is approximately 10 billion years.

Time measurement and standards

Major subjects	Time Chronometry Orders of magnitude Metrology

International standards	UTC UTC offset UT ΔT DUT1 IERS ISO 31-1 ISO 8601 TAI 12-hour clock 24-hour clock Barycentric Coordinate Time Civil time Daylight saving time Geocentric Coordinate Time International Date Line Leap second Solar time Terrestrial Time Time zone

Obsolete standards	Barycentric Dynamical Time Ephemeris time Greenwich Mean Time Prime meridian

Time in physics	Absolute time and space Spacetime Chronon Continuous time Coordinate time Cosmological decade Discrete time Planck epoch Planck time Proper time Theory of relativity Time dilation Gravitational time dilation Time domain T-symmetry

Horology	Clock Astrarium Atomic clock Complication Equation of time History of timekeeping devices Hourglass Marine chronometer Marine sandglass Radio clock Sundial Watch Water clock

Calendar	Astronomical Dominical letter Epact Equinox Gregorian Hebrew Hindu Intercalation Islamic Julian Leap year Lunar Lunisolar Seven-day week Solar Solstice Tropical year Weekday determination Weekday names

Archaeology and geology	Dating methodologies Geologic time scale International Commission on Stratigraphy

Astronomical chronology	Galactic year Nuclear time scale Precession Sidereal time

Units of time	Century Day Decade Fortnight Hour Jiffy Lustrum Millennium Minute Month Paksha Saeculum Second Shake Tide Week Year

Related topics	Chronology Duration Mental chronometry Metric time System time Time value of money Timekeeper

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