Constants ========= Physical, mathematical and astrophysical constants available in the Galacticus source (defined via ```` directives). Constants whose value is provided by the GNU Scientific Library note the GSL symbol rather than a literal value. Astrophysical constants ----------------------- ``arcminutesToDegrees`` = ``1.0d0/60.0e0`` [:math:`^\circ/^\prime`] Conversion factor from arcminutes to degrees. Defined. ``arcsecondsToDegrees`` = ``1.0d0/3600.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from arcseconds to degrees. Defined. ``degreesToRadians`` = ``2.0d0*Pi/360.0e0`` [:math:`\mathrm{rad}/^\circ`] Conversion factor from degrees to radians. Defined. ``gigayear`` = ``giga*year`` (:math:`\mathrm{Gyr}`) [s] Gigayear---:math:`10^9` years. Derived.; `more `_ ``heliumByMassPrimordial`` = ``0.2486e+00`` (:math:`\mathrm{Y}_\mathrm{p}`) Primordial helium fraction by mass. (Theoretical expectation based on WMAP results.) \cite{cyburt_update_2008} ``heliumByMassSolar`` = ``0.2740e0`` (:math:`\mathrm{Y}_\odot`) Solar helium fraction by mass. `Allen's Astrophysical Quantities, page 28 `_ ``heliumToHydrogenAbundancePrimordial`` = ``(heliumByMassPrimordial/atomicMassHelium)/(hydrogenByMassPrimordial/atomicMassHydrogen)`` (:math:`\mathrm{He/H}_\mathrm{p}`) Primordial helium to hydrogen ratio by number. Derived. ``heliumToHydrogenAbundanceSolar`` = ``(heliumByMassSolar/atomicMassHelium)/(hydrogenByMassSolar/atomicMassHydrogen)`` (:math:`\mathrm{He/H}_\odot`) Solar helium to hydrogen ratio by number. Derived. ``hoursToDegrees`` = ``360.0d0/24.0e0`` [:math:`^\circ/^{\prime}`] Conversion factor from hours to degrees. Defined. ``hoursToRadians`` = ``2.0d0*Pi/24.0e0`` [:math:`\mathrm{rad}/^{\prime}`] Conversion factor from hours to radians. Defined. ``hydrogenByMassPrimordial`` = ``0.7514e+00`` (:math:`\mathrm{X}_\mathrm{p}`) Primordial hydrogen fraction by mass. \cite{cyburt_update_2008} ``hydrogenByMassSolar`` = ``0.7070e0`` (:math:`\mathrm{X}_\odot`) Solar hydrogen fraction by mass. `Allen's Astrophysical Quantities, page 28 `_ ``kiloParsec`` = ``kilo*parsec`` (:math:`\mathrm{kpc}`) [m] Kiloparsec---:math:`10^3` parsecs. Derived.; `more `_ ``lithiumToHydrogenAbundancePrimordial`` = ``5.2400e-10`` (:math:`\mathrm{Z}_\mathrm{Li,p}`) Primordial lithium fraction by mass. \cite{cyburt_update_2008} ``luminositySolar`` = ``3.845e26`` (:math:`\mathrm{L}_\odot`) [W] Solar luminosity. `Allen's Astrophysical Quantities, page 340 `_ ``luminosityZeroPointAB`` = ``(10.0d0**(-offsetAB/2.5d0))*4.0d0*Pi*((10.0d0*parsec*hecto)**2)*ergs`` [W/Hz] The luminosity zero point offset in the AB magnitude system, found by computing the flux of a zeroth magnitude source at 10pc. \cite{oke_secondary_1983}; `more `_ ``massSolar`` (:math:`\mathrm{M}_\odot`) [kg] Solar mass. value from GSL ``GSL_CONST_MKSA_SOLAR_MASS``; `Gnu Scientific Library `_ ``meanAtomicMassPrimordial`` = ``1.0d0/(2.0d0*hydrogenByMassPrimordial/atomicMassHydrogen+3.0d0*heliumByMassPrimordial/atomicMassHelium)`` (:math:`\mu_\mathrm{p}`) Primordial mean atomic mass. Derived. ``megaParsec`` = ``mega*parsec`` (:math:`\mathrm{Mpc}`) [m] Megaparsec---:math:`10^6` parsecs. Derived.; `more `_ ``metallicityPrimordial`` = ``lithiumToHydrogenAbundancePrimordial*atomicMassLithium7/atomicMassHydrogen`` (:math:`\mathrm{Z}_\mathrm{p}`) Primordial metallicity. Derived. ``metallicitySolar`` = ``0.0188e0`` (:math:`\mathrm{Z}_\odot`) Solar metal fraction by mass. `Allen's Astrophysical Quantities, page 28 `_ ``minutesToDegrees`` = ``360.0d0/24.0d0/60.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from minutes to degrees. Defined. ``MpcPerKmPerSToGyr`` = ``megaParsec/kilo/gigaYear`` [Mpc/km s\ :math:`^{-1}`/Gyr] The conversion from Mpc/(km s\ :math:`^{-1})` to Gyr. Derived. ``offsetAB`` = ``48.57e0`` The zero point offset in the AB magnitude system: :math:`m = -2.5\log_{10}(F_\nu/\mathrm{[ergs/s/cm}^2\mathrm{/Hz]})-48.57`. This zero point is chosen such that AB and Vega magnitude systems agree in the V-band. The original definition of the AB system zero point used a value of :math:`48.60` :cite:p:`oke_secondary_1983` to achieve this. However, more `recent measurements `_ give Vega a magnitude of :math:`+0.03` in the Vega magnitude system, which is why the AB magnitude zero point is now also shifted by :math:`0.03` relative to the original definition. \cite{oke_secondary_1983}; `more `_ ``opticalDepthToMagnitudes`` = ``2.5d0/log(10.0d0)`` The conversion factor between magnitudes of extinction and optical depth. Derived. ``parsec`` (:math:`\mathrm{pc}`) [m] Parsec---the distance at which 1 AU subtends an angle of one arcsecond. value from GSL ``GSL_CONST_MKSA_PARSEC``; `Gnu Scientific Library `_; `more `_ ``radiusSolar`` = ``6.95508e8`` (:math:`\mathrm{R}_\odot`) [m] Solar radius. `Allen's Astrophysical Quantities, page 340 `_ ``secondsToDegrees`` = ``360.0d0/24.0d0/3600.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from seconds to degrees. Defined. Atomic physics constants ------------------------ ``atomicMassHelium`` = ``4.0026032545e0`` (:math:`A_{^4\mathrm{He}}`) [amu] Atomic mass of the :math:`^4`\ He isotope of helium. `Commission on Isotopic Abundances and Atomic Weights `_ ``atomicMassHydrogen`` = ``1.0078250322e0`` (:math:`A_{^1\mathrm{H}}`) [amu] Atomic mass of the :math:`^1`\ H isotope of hydrogen. `Commission on Isotopic Abundances and Atomic Weights `_ ``atomicMassLithium7`` = ``7.01600344e0`` (:math:`A_{^7\mathrm{Li}}`) [amu] Atomic mass of the :math:`^7`\ Li isotope of lithium. `Commission on Isotopic Abundances and Atomic Weights `_ ``atomicMassUnit`` (:math:`\mathrm{u}`) [kg] The unified atomic mass unit. value from GSL ``GSL_CONST_MKSA_UNIFIED_ATOMIC_MASS``; `Gnu Scientific Library `_ ``lymanSeriesLimitWavelengthHydrogen_atomic`` = ``+plancksConstant*speedLight/rydberg*metersToAngstroms/(+1.0d0-electronMass/massHydrogenAtom)`` (:math:`R^{-1}_\mathrm{H}`) [:math:`\AA`] Hydrogen Lyman series limit wavelength including correction for finite mass of the atom. Derived.; `more `_ ``massHeliumAtom`` = ``atomicMassHelium*atomicMassUnit`` (:math:`m_\mathrm{He}`) [kg] Mass of the :math:`^4`\ He isotope of helium. Derived ``massHydrogenAtom`` = ``atomicMassHydrogen*atomicMassUnit`` (:math:`m_\mathrm{H}`) [kg] Mass of the :math:`^1`\ H isotope of hydrogen. Derived ``rydberg`` (:math:`\mathrm{Ry}`) [J] Rydberg---the ionization energy of hydrogen in its ground state. value from GSL ``GSL_CONST_MKSA_RYDBERG``; `Gnu Scientific Library `_ GNU Scientific Library constants -------------------------------- ``CBLAS_Diag`` Enumeration of whether a CBLAS triangular matrix has unit diagonal or not. value from GSL ``CBLAS_DIAG``; Gnu Scientific Library ``CBLAS_Transpose`` Enumeration of CBLAS transpose options. value from GSL ``CBLAS_TRANSPOSE``; Gnu Scientific Library ``CBLAS_UpLo`` Enumeration of CBLAS matrix upper/lower options. value from GSL ``CBLAS_UPLO``; Gnu Scientific Library ``GSL_Continue`` Error code for iteration has not converged. value from GSL ``GSL_CONTINUE``; `Gnu Scientific Library `_ ``GSL_EBadFunc`` Error code for problem with user-supplied function. value from GSL ``GSL_EBADFUNC``; `Gnu Scientific Library `_ ``GSL_EBadTol`` Error code for user-specified invalid tolerance. value from GSL ``GSL_EBADTOL``; `Gnu Scientific Library `_ ``GSL_EDom`` Error code for input domain error, e.g sqrt(-1). value from GSL ``GSL_EDOM``; `Gnu Scientific Library `_ ``GSL_EMaxIter`` Error code for exceeding the maximum number of iterations. value from GSL ``GSL_EMAXITER``; `Gnu Scientific Library `_ ``GSL_ENoProg`` Error code for iteration not making progress towards solution. value from GSL ``GSL_ENOPROG``; `Gnu Scientific Library `_ ``GSL_ERange`` Error code for output range error, e.g. exp(1e100). value from GSL ``GSL_ERANGE``; `Gnu Scientific Library `_ ``GSL_ERound`` Error code for failure because of roundoff error. value from GSL ``GSL_EROUND``; `Gnu Scientific Library `_ ``GSL_ESing`` Error code for apparent singularity detected. value from GSL ``GSL_ESING``; `Gnu Scientific Library `_ ``GSL_ETol`` Error code for failure to reach the specified tolerance. value from GSL ``GSL_ETOL``; `Gnu Scientific Library `_ ``GSL_EUndrFlw`` Error code for underflow. value from GSL ``GSL_EUNDRFLW``; `Gnu Scientific Library `_ ``GSL_EZeroDiv`` Error code for attempt to divide by zero. value from GSL ``GSL_EZERODIV``; `Gnu Scientific Library `_ ``GSL_Failure`` Error code for generic failure. value from GSL ``GSL_FAILURE``; `Gnu Scientific Library `_ ``GSL_Integ_Gauss15`` Indicator for 15-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS15``; `GSL `_ ``GSL_Integ_Gauss21`` Indicator for 21-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS21``; `GSL `_ ``GSL_Integ_Gauss31`` Indicator for 31-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS31``; `GSL `_ ``GSL_Integ_Gauss41`` Indicator for 41-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS41``; `GSL `_ ``GSL_Integ_Gauss51`` Indicator for 51-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS51``; `GSL `_ ``GSL_Integ_Gauss61`` Indicator for 61-point Gauss-Kronrod integration rule. value from GSL ``GSL_INTEG_GAUSS61``; `GSL `_ ``GSL_Prec_Approx`` Specifies GSL approximate-precision mode. value from GSL ``GSL_PREC_APPROX``; Gnu Scientific Library ``GSL_Prec_Double`` Specifies GSL double-precision mode. value from GSL ``GSL_PREC_DOUBLE``; Gnu Scientific Library ``GSL_Prec_Single`` Specifies GSL single-precision mode. value from GSL ``GSL_PREC_SINGLE``; Gnu Scientific Library ``GSL_Success`` Error code for success. value from GSL ``GSL_SUCCESS``; `Gnu Scientific Library `_ Kernel constants ---------------- ``Kernel_EACCES`` Error code for permission denied. `Linux kernel man pages `_ ``Kernel_ELOOP`` Error code for loop exists in symbolic links. `Linux kernel man pages `_ ``Kernel_EMLINK`` Error code for too many links. `Linux kernel man pages `_ ``Kernel_ENAMETOOLONG`` Error code for name too long. `Linux kernel man pages `_ ``Kernel_ENOENT`` Error code for non-existent directory. `Linux kernel man pages `_ ``Kernel_ENOSPC`` Error code for no space on file system. `Linux kernel man pages `_ ``Kernel_ENOTDIR`` Error code for not a directory. `Linux kernel man pages `_ ``Kernel_EROFS`` Error code for read only file system. `Linux kernel man pages `_ Mathematical constants ---------------------- ``catalan`` = ``0.91596559417721901505460351493238411077e0`` (:math:`G`) Catalan's constant. `OEIS: A006752 `_; `more `_ ``e`` (:math:`\mathrm{e}`) Euler's number---the base of natural logarithms. value from GSL ``M_E``; `Gnu Scientific Library `_; `more `_ ``eulersConstant`` (:math:`\gamma`) Euler's constant. value from GSL ``M_EULER``; `Gnu Scientific Library `_; `more `_ ``ln10`` (:math:`\log 10`) The natural logarithm of 10. value from GSL ``M_LN10``; `Gnu Scientific Library `_ ``ln2`` (:math:`\log 2`) The natural logarithm of 2. value from GSL ``M_LN2``; `Gnu Scientific Library `_ ``Pi`` (:math:`\pi`) The ratio of a circle's perimeter to its diameter. value from GSL ``M_PI``; `Gnu Scientific Library `_; `more `_ ``PiQuadPrecision`` = ``3.141592653589793238462643383279502884197`` (:math:`\pi`) The ratio of a circle's perimeter to its diameter (to quadruple precision). `OEIS: A002117 `_; `more `_ ``riemannZeta3`` = ``1.20205690315959428539973816151144999076e0`` (:math:`\zeta(3)`) Riemann zeta function evaluated at :math:`s=3`. `OEIS: A002117 `_; `more `_ Physical constants ------------------ ``boltzmannsConstant`` (:math:`\mathrm{k}`) [J/K] Boltzmann's constant. value from GSL ``GSL_CONST_MKSA_BOLTZMANN``; `Gnu Scientific Library `_ ``electronCharge`` (:math:`\mathrm{e}`) [C] The charge of the electron. value from GSL ``GSL_CONST_MKSA_ELECTRON_CHARGE``; `Gnu Scientific Library `_ ``electronMass`` (:math:`\mathrm{m}_\mathrm{e}`) [kg] The mass of an electron. value from GSL ``GSL_CONST_MKSA_MASS_ELECTRON``; `Gnu Scientific Library `_ ``electronRadius`` = ``1.0d0/(4.0d0*Pi*permittivityFreeSpace)*electronCharge**2/(electronMass*speedLight**2)`` (:math:`r_\mathrm{e}`) [m] The classical electron radius. Definition.; `more `_ ``fineStructure`` (:math:`\alpha`) The electromagnetic fine structure constant. value from GSL ``GSL_CONST_NUM_FINE_STRUCTURE``; `Gnu Scientific Library `_ ``gravitationalConstant`` (:math:`\mathrm{G}`) [N m\ :math:`^2` kg\ :math:`^{-2}`] The gravitational constant. value from GSL ``GSL_CONST_MKSA_GRAVITATIONAL_CONSTANT``; `Gnu Scientific Library `_ ``gravitationalConstant_internal`` = ``gravitationalConstant*massSolar/(kilo**2)/megaParsec`` [km\ :math:`^2`\ s\ :math:`^{-2}`\ Mpc/:math:`\mathrm{M}_\odot`] Newton's gravitational constant in Galacticus' :math:`\mathrm{M}_\odot`, Mpc, km/s unit system. Derived. ``permittivityFreeSpace`` (:math:`\epsilon_0`) [m/s] The permittivity of free space. value from GSL ``GSL_CONST_MKSA_VACUUM_PERMITTIVITY``; `Gnu Scientific Library `_ ``plancksConstant`` (:math:`\mathrm{h}`) [J s] Planck's constant. value from GSL ``GSL_CONST_MKSA_PLANCKS_CONSTANT_H``; `Gnu Scientific Library `_ ``radiationConstant`` = ``4.0d0*stefanBoltzmannConstant/speedLight`` (:math:`a`) [J/m\ :math:`^3`/K\ :math:`^4`] The radiation density constant. Definition.; `more `_ ``speedLight`` (:math:`\mathrm{c}`) [m/s] The speed of light in vacuum. value from GSL ``GSL_CONST_MKSA_SPEED_OF_LIGHT``; `Gnu Scientific Library `_; `more `_ ``stefanBoltzmannConstant`` (:math:`\sigma`) [J/s/m\ :math:`^2`/K\ :math:`^4`] The Stefan-Boltzmann constant. value from GSL ``GSL_CONST_MKSA_STEFAN_BOLTZMANN_CONSTANT``; `Gnu Scientific Library `_ ``thomsonCrossSection`` (:math:`\sigma_\mathrm{T}`) [m/s] The Thompson cross-section. value from GSL ``GSL_CONST_MKSA_THOMSON_CROSS_SECTION``; `Gnu Scientific Library `_ SI prefixes ----------- ``atto`` = ``1.0e-18`` (:math:`\mathrm{a}`) SI prefix. `NIST `_ ``centi`` = ``1.0e-02`` (:math:`\mathrm{c}`) SI prefix. `NIST `_ ``deca`` = ``1.0e+01`` (:math:`\mathrm{da}`) SI prefix. `NIST `_ ``deci`` = ``1.0e-01`` (:math:`\mathrm{d}`) SI prefix. `NIST `_ ``exa`` = ``1.0e+18`` (:math:`\mathrm{E}`) SI prefix. `NIST `_ ``femto`` = ``1.0e-15`` (:math:`\mathrm{f}`) SI prefix. `NIST `_ ``giga`` = ``1.0e+09`` (:math:`\mathrm{G}`) SI prefix. `NIST `_ ``hecto`` = ``1.0e+02`` (:math:`\mathrm{h}`) SI prefix. `NIST `_ ``kilo`` = ``1.0e+03`` (:math:`\mathrm{k}`) SI prefix. `NIST `_ ``mega`` = ``1.0e+06`` (:math:`\mathrm{M}`) SI prefix. `NIST `_ ``micro`` = ``1.0e-06`` (:math:`\mu`) SI prefix. `NIST `_ ``milli`` = ``1.0e-03`` (:math:`\mathrm{m}`) SI prefix. `NIST `_ ``nano`` = ``1.0e-09`` (:math:`\mathrm{n}`) SI prefix. `NIST `_ ``peta`` = ``1.0e+15`` (:math:`\mathrm{P}`) SI prefix. `NIST `_ ``pico`` = ``1.0e-12`` (:math:`\mathrm{p}`) SI prefix. `NIST `_ ``quecto`` = ``1.0e-30`` (:math:`\mathrm{q}`) SI prefix. `NIST `_ ``quetta`` = ``1.0e+30`` (:math:`\mathrm{Q}`) SI prefix. `NIST `_ ``ronna`` = ``1.0e+27`` (:math:`\mathrm{R}`) SI prefix. `NIST `_ ``ronto`` = ``1.0e-27`` (:math:`\mathrm{r}`) SI prefix. `NIST `_ ``tera`` = ``1.0e+12`` (:math:`\mathrm{T}`) SI prefix. `NIST `_ ``yocto`` = ``1.0e-24`` (:math:`\mathrm{y}`) SI prefix. `NIST `_ ``yotta`` = ``1.0e+24`` (:math:`\mathrm{Y}`) SI prefix. `NIST `_ ``zepto`` = ``1.0e-21`` (:math:`\mathrm{z}`) SI prefix. `NIST `_ ``zetta`` = ``1.0e+21`` (:math:`\mathrm{Z}`) SI prefix. `NIST `_ Units ----- ``arcminutesToDegrees`` = ``1.0d0/60.0e0`` [:math:`^\circ/^\prime`] Conversion factor from arcminutes to degrees. Defined. ``arcsecond`` = ``Pi/180.0d0/60.0d0/60.0e0`` (:math:`^{\prime\prime}`) [rad] Arcsecond---unit of angle. Derived; `more `_ ``arcsecondsToDegrees`` = ``1.0d0/3600.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from arcseconds to degrees. Defined. ``atomicMassUnit`` (:math:`\mathrm{u}`) [kg] The unified atomic mass unit. value from GSL ``GSL_CONST_MKSA_UNIFIED_ATOMIC_MASS``; `Gnu Scientific Library `_ ``barn`` = ``1.0e-28`` (:math:`\mathrm{b}`) [m\ :math:`^2`] Unit of area used for nuclear cross-sections. `IUPAC Gold Book `_; `more `_ ``degree`` = ``Pi/180.0e0`` (:math:`^\circ`) [rad] Degree---unit of angle. Derived; `more `_ ``degreesToRadians`` = ``2.0d0*Pi/360.0e0`` [:math:`\mathrm{rad}/^\circ`] Conversion factor from degrees to radians. Defined. ``electronVolt`` (:math:`\mathrm{eV}`) [J] Electron-volt---the energy of an electron accelerated through a 1 volt electric field. value from GSL ``GSL_CONST_MKSA_ELECTRON_VOLT``; `Gnu Scientific Library `_ ``ergs`` = ``1.0e-7`` (:math:`\mathrm{ergs}`) [J] Unit of energy in the CGS system. \cite{jackson_classical_1999}; `more `_ ``gigayear`` = ``giga*year`` (:math:`\mathrm{Gyr}`) [s] Gigayear---:math:`10^9` years. Derived.; `more `_ ``gravitationalConstant_internal`` = ``gravitationalConstant*massSolar/(kilo**2)/megaParsec`` [km\ :math:`^2`\ s\ :math:`^{-2}`\ Mpc/:math:`\mathrm{M}_\odot`] Newton's gravitational constant in Galacticus' :math:`\mathrm{M}_\odot`, Mpc, km/s unit system. Derived. ``hoursToDegrees`` = ``360.0d0/24.0e0`` [:math:`^\circ/^{\prime}`] Conversion factor from hours to degrees. Defined. ``hoursToRadians`` = ``2.0d0*Pi/24.0e0`` [:math:`\mathrm{rad}/^{\prime}`] Conversion factor from hours to radians. Defined. ``kiloParsec`` = ``kilo*parsec`` (:math:`\mathrm{kpc}`) [m] Kiloparsec---:math:`10^3` parsecs. Derived.; `more `_ ``megaParsec`` = ``mega*parsec`` (:math:`\mathrm{Mpc}`) [m] Megaparsec---:math:`10^6` parsecs. Derived.; `more `_ ``metersToAngstroms`` = ``1.0e10`` (:math:`\text{\AA}/\mathrm{m}`) [\AA/m] Number of Angstroms per meter. Defined. ``micronsToAngstroms`` = ``1.0e4`` (:math:`\text{\AA}/\mu\mathrm{m}`) [Å/:math:`\mu`\ m] Number of Angstroms per micron. Defined. ``minutesToDegrees`` = ``360.0d0/24.0d0/60.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from minutes to degrees. Defined. ``MpcPerKmPerSToGyr`` = ``megaParsec/kilo/gigaYear`` [Mpc/km s\ :math:`^{-1}`/Gyr] The conversion from Mpc/(km s\ :math:`^{-1})` to Gyr. Derived. ``parsec`` (:math:`\mathrm{pc}`) [m] Parsec---the distance at which 1 AU subtends an angle of one arcsecond. value from GSL ``GSL_CONST_MKSA_PARSEC``; `Gnu Scientific Library `_; `more `_ ``rydberg`` (:math:`\mathrm{Ry}`) [J] Rydberg---the ionization energy of hydrogen in its ground state. value from GSL ``GSL_CONST_MKSA_RYDBERG``; `Gnu Scientific Library `_ ``secondsToDegrees`` = ``360.0d0/24.0d0/3600.0e0`` [:math:`^\circ/^{\prime\prime}`] Conversion factor from seconds to degrees. Defined. ``year`` = ``3.15581497635456e7`` (:math:`\mathrm{yr}`) [s] Sidereal year. `Earth observation center. `_; `more `_